DEVELOPMENT, ANALYSIS, and TESTING of PNEUMATIC and HYBRID VEHICLE POWERING OPTIONS by REZA MOHAMMADALI ZADEH a Thesis Submitted

DEVELOPMENT, ANALYSIS, AND TESTING OF PNEUMATIC AND HYBRID VEHICLE POWERING OPTIONS

REZA MOHAMMADALI ZADEH

A Thesis Submitted in Partial Fulfillment of the Requirement for the degree of Doctor of Philosophy in Mechanical Engineering

Faculty of Engineering and Applied Science University of Ontario Institute of Technology (Ontario Tech University) Oshawa, Ontario, Canada

February 2020

THESIS EXAMINATION INFORMATION

Submitted by: REZA MOHAMMADALI ZADEH

Degree of Doctor of Philosophy in Mechanical Engineering

Thesis title: Development, analysis, and testing of pneumatic and hybrid vehicle powering options

An oral defense of this thesis took place on January 16, 2020 in front of the following examining committee:

Examining Committee:

Chair of Examining Committee Dr. Dipal Patel

Research Supervisor Dr. Ibrahim Dincer

Examining Committee Member Dr. Ahmad Barari

Examining Committee Member Dr. Martin Agelin-Chaab

University Examiner Dr. Moustafa El-Gindy

External Examiner Dr. Mohamed S. Hamed

The above committee determined that the thesis is acceptable in form and content and that a satisfactory knowledge of the field covered by the thesis was demonstrated by the candidate during an oral examination. A signed copy of the Certificate of Approval is available from the School of Graduate and Postdoctoral Studies. AUTHOR’S DECLARATION

I hereby declare that this thesis consists of original work of which I have authored. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners.

I authorize the University of Ontario Institute of Technology (Ontario Tech University) to lend this thesis to other institutions or individuals for the purpose of scholarly research. I further authorize University of Ontario Institute of Technology (Ontario Tech University) to reproduce this thesis by photocopying or by other means, in total or in part, at the request of other institutions or individuals for the purpose of scholarly research. I understand that my thesis will be made electronically available to the public.

REZA MOHAMMADALI ZADEH

ABSTRACT In this thesis, a conceptual systems development study and an experimental investigation on pneumatic and hybrid powered vehicles are undertaken comprehensively. The conceptual development study includes ten novel integrated energy systems to function as potential powering options for vehicle applications. These systems are analyzed using energy and exergy approaches together with a parametric study to determine the effect of varying different designing and surrounding parameters on the performances of the introduced systems. The feasibility of using compressed air as an energy carrier to propel a light vehicle is also studied. The analysis is based on thermodynamic, economic and environmental impact. It is shown that the expected mechanical energy developed by the compressed air car is around 3 MJ per 100- liter tank of air compressed at 350 bar. The cryogenic nitrogen option is found to be better in regard to energy storage; about 7 MJ of mechanical energy can be retrieved from a 100-liter tank. The expected driving range of a compressed air vehicle is of the order of tens of km, depending on the vehicle size. The range can be approximately determined to be 46 km for a pure compressed air vehicle with 300 liters of air at a pressure of 350 bar. The experimental part of the thesis focuses on the development, building and testing of three fully integrated prototype systems for a pneumatic vehicle. These prototypes include a compressed air system integrated with a heating element, a compressed air system integrated with a phase change material heat exchanger and a hybrid integrated compressed air-electric system. The developed systems are analyzed using energy and exergy approaches and a parametric study is performed to identify the effect of varying operating parameters on the system performance. The driving ranges of the developed systems are determined to vary between 128-140 km. Hybrid systems show a driving range comparable with that of gasoline vehicles, but with substantially lower the greenhouse gas emissions. The compressed air stations are also studied as part of this work, and a series of technical recommendations are listed at the end of this thesis.

Keywords: Compressed air vehicles, powering options, hybrid vehicles, energy, exergy, efficiency.

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STATEMENT OF CONTRIBUTIONS

I hereby certify that I am the sole author of this thesis and that no part of this thesis has been published or submitted for publication. I have used standard referencing practices to acknowledge ideas, research techniques, or other materials that belong to others. Furthermore, I hereby certify that I am the sole source of the creative works and/or inventive knowledge described in this thesis.

ACKNOWLEDGEMENTS

I would like to express my deepest gratitude to my supervisor, Prof. Dr. Ibrahim Dincer, for his exemplary guidance, care and patience and for providing me with a remarkable atmosphere for research. His immense knowledge, constant guidance, intellect, devotion, and passion as a scientist encouraged me, throughout my research voyage, to be more dedicated and committed. He afforded me a great opportunity to work under his guidance, patience, and concern, which helped me to think beyond my limitations. I would not have been able to finish this thesis without his enthusiasm, support, useful advice and recommendations. He is, and always will be, my academic and spiritual mentor. I would also like to thank the examining committee members, Dr. Ahmad Barari, Dr. Martin Agelin-Chaab, Dr. Moustafa El-Gindy, Dr. Mohamed S. Hamed and Dr. Dipal Patel for their valuable feedbacks and comments in further improving my thesis. I am truly grateful to my dear friends, Farrukh Khalid, Muhammad Ezzat, Yusuf Bicer, Murat Demir, Farid Safari, Nader Javani, and Osamah Siddiqui, for their endless humor, advice, and company on this journey. I would also like to thank Janette Hogerwaard, Maan Al-Zareer, Ahmed Hassan and past or current friends and colleagues in ACE 3030b who helped me during the preparation of this thesis. I also sincerely thank Dr. Calin Zamfirescu for always being so generous in sharing his knowledge. Special thanks go to Mr. Craig Antrobus, Chairman and CEO of Antrobus Technology, who has encouraged me to work harder. Furthermore, the financial support from Mitacs and Antrobus Consulting Ltd. is greatly acknowledged. Last but not least, I would like to express my gratitude to my parents, my wife and my two sons for their limitless support, fortitude, inspiration and reassurance throughout my life. I am so lucky to have such an impressive and strong family supporting me. This research would not exist without all of you.

TABLE OF CONTENTS

THESIS EXAMINATION INFORMATION ...... i ABSTRACT ...... ii AUTHOR’S DECLARATION ...... iii STATEMENT OF CONTRIBUTIONS ...... iv ACKNOWLEDGEMENTS ...... v TABLE OF CONTENTS ...... vi LIST OF TABLES ...... x LIST OF FIGURES ...... xii NOMENCLATURE ...... xvi CHAPTER 1: INTRODUCTION ...... 1 1.1 World energy and environmental outlook ...... 1 1.2 Transportation Options ...... 3 1.3 Powering Options for Vehicles ...... 3 1.4 Conventional Fuels ...... 4 1.5 Renewable Fuels ...... 4 1.6 Electric Options ...... 6 1.7 Compressed Air ...... 7 1.8 Electric and Hybrid Electric Vehicles ...... 9 1.9 Sustainable Energy, Vehicles and GHG Emissions ...... 13 1.10 Motivation ...... 15 1.11 Objectives ...... 16 1.12 Novelties ...... 17 CHAPTER 2: LITERATURE REVIEW ...... 18 2.1 Experimental compressed gas and hybrid vehicles ...... 18 2.2 Compressed/liquid gas vehicles ...... 20 2.3 Compressed gas and combustion engine hybrid vehicles ...... 22 2.4 Compressed gas and electric hybrid vehicles ...... 24 2.5 Comparative study of hybrid vehicles ...... 25

CHAPTER 3: CONCEPTUAL DEVELOPMENT OF PNEUMATIC CONFIGURATIONS ...... 29 3.1 Introduction ...... 29 3.2 Compressed air ...... 30 3.3 Compressed nitrogen vehicle ...... 31 3.4 Liquid nitrogen vehicle ...... 33 3.5 Compressed carbon dioxide ...... 34 3.6 Compressed Air, Internal Combustion and Hydrogen Vehicle ...... 36 3.7 Compressed air, internal combustion engine and compressed natural gas ...... 37 3.8 Compressed air, internal combustion engine and liquid propane gas ...... 38 3.9 Internal combustion engine and compressed air system ...... 39 3.10 Compressed air, internal combustion engine with heat recovery ...... 40 3.11 Internal combustion engine and compressed air four-stage expansion ...... 40 CHAPTER 4: EXPERIMENTAL APPARATUS AND PROCEDURE ...... 42 4.1 Introduction ...... 42 4.2 Compressed air system with heating element prototype ...... 44 4.2.1 Description of prototype system 1 ...... 44 4.2.2 Experimental procedures for prototype 1 ...... 45 4.3 Compressed air system with PCM heat exchanger prototype ...... 47 4.3.1 Description of prototype 2 system ...... 47 4.3.2 Experimental procedures for prototype 2 ...... 48 4.4 Hybrid compressed air-electric system prototype ...... 50 4.4.1 Description of prototype 3 system ...... 50 4.4.2 Experimental procedures for prototype 3 ...... 51 4.5 Experimental system elements, tools and parameters ...... 53 4.6 Experimental error and measurement uncertainties ...... 59 CHAPTER 5: ANALYSIS AND MODELING ...... 61 5.1 Introduction ...... 61 5.2 Thermodynamic analysis ...... 61 5.3 Compressed air system with a heating element ...... 63

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5.3.1 Air motors ...... 63 5.3.2 Turbine ...... 63 5.3.3 Mixer A and B ...... 63 5.3.4 Valve ...... 64 5.3.5 Regulator ...... 64 5.3.6 Energy and exergy efficiencies of a compressed air system with a heating element 65 5.4 Compressed air system with PCM heat exchanger analysis ...... 65 5.4.1 Heat storage unit (in PCM) ...... 65 5.4.2 Air motor ...... 66 5.4.3 Turbine ...... 66 5.4.4 Mixer A and B ...... 67 5.4.5 Valve ...... 67 5.4.6 Regulator ...... 68 5.4.7 Heat exchanger ...... 68 5.4.8 Energy and exergy efficiencies of system 2 ...... 68 5.5 Hybrid compressed air-electric system analysis ...... 69 5.5.1 Heat storage (PCM) unit ...... 69 5.5.2 Air motor ...... 70 5.5.3 Turbine ...... 70 5.5.4 Mixer A and B ...... 70 5.5.5 Valve ...... 71 5.5.6 Regulator ...... 71 5.5.7 Heat exchanger ...... 71 5.5.8 Energy and exergy efficiencies of the hybrid compressed air-electric prototype ..... 72 5.6 Photovoltaic system ...... 72 5.7 Mechanical analysis ...... 73 5.8 Aspen-plus simulation ...... 74 CHAPTER 6: RESULTS AND DISCUSSION ...... 76 6.1 Experimental system results ...... 76 6.1.1 Measurement uncertainties ...... 76

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6.1.2 Compressed air system with heating element results ...... 78 6.1.3 Compressed air system with a PCM heat exchanger results ...... 87 6.1.4 Hybrid compressed air-electric system results ...... 93 6.2 Simulation results ...... 99 6.2.1 Introduction ...... 99 6.2.2 Pure compressed air system results ...... 100 6.2.3 Pure compressed nitrogen vehicle system results ...... 103 6.2.4 Pure liquid nitrogen vehicle system results ...... 104 6.2.5 Pure compressed carbon dioxide system results ...... 106 6.2.6 Compressed air, internal combustion and hydrogen vehicle results ...... 108 6.2.7 Compressed air, internal combustion engine and compressed natural gas results .. 109 6.2.8 Compressed air, internal combustion engine and liquid propane gas vehicle ...... 110 6.2.9 Internal combustion engine and compressed air results ...... 111 6.2.10 Compressed air and the internal combustion engine with heat recovery results ... 112 6.2.11 Internal combustion engine and compressed air with four-stage expansion ...... 113 6.3 Compressed gas maximum work ...... 116 6.4 Compressed gas storage optimization ...... 122 6.5 Comparison of systems ...... 124 6.5.1 Comparison of experimental systems ...... 124 6.5.2 Comparison of Simulated Systems ...... 125 CHAPTER 7: CONCLUSIONS AND RECOMMENDATIONS ...... 128 7.1 Conclusions ...... 128 7.2 Recommendations ...... 129 REFERENCES ...... 131

LIST OF TABLES

Table 4.1: Technical data related to system elements ...... 53 Table 4.2: Technical data of system devices and equipment ...... 57 Table 4.3: Measurement device accuracy and range ...... 59 Table 5.1: Data used in the parametric study for the photovoltaic model ...... 73 Table 6.1: Measurement uncertainties ...... 77 Table 6.2: Overall exergy and energy efficiencies of a compressed air system with a heating element ...... 79 Table 6.3: Exergy destruction rates of the major components of prototype 1 ...... 80 Table 6.4: Comparison results of experimental and theoretical state point properties ...... 81 of a compressed air system with a heating element ...... 81 Table 6.5: Simulation results of the compressed air system with a heating element ...... 83 Table 6.6: Overall exergy and energy efficiencies of a compressed air system with a pcm heat exchanger ...... 88 Table 6.7: Exergy destruction rates of major components of prototype 2 ...... 89 Table 6.8: Comparison results of experimental and theoretical state point properties ...... 90 of the compressed air system with a PCM heat exchanger ...... 90 Table 6.9: Simulation results of the compressed air system with a heating element ...... 91 Table 6.10: Overall exergy and energy efficiencies of the hybrid compressed air-electric prototype ...... 94 Table 6.11: Exergy destruction rates of the major components of prototype 3 ...... 96 Table 6.12: Comparison results of experimental and theoretical state point properties ...... 97 of the hybrid compressed air-electric ...... 97 Table 6.13: Simulation results of the compressed air system with a heating element ...... 97 Table 6.14: PCM and TES substance properties and results ...... 98 Table 6.15: Simulation parameters for system 1 ...... 101 Table 6.16: Hydrogen and air parameters determined for system 5 ...... 108 Table 6.17: Main parameters of air and natural gas for system 7 ...... 109 Table 6.18: System 7 results ...... 110

Table 6.19: System 10 inlet-outlet conditions ...... 113 Table 6.20: Simulation results for system 10 ...... 115 Table 6.21: Comparison of the three built and tested prototypes ...... 124 Table 6.22: Comparison of 3 prototypes with compressed air car 1, 2 and 3 ...... 125 Table 6.23: Simulation parameters for system ...... 126 Table 6.24: Comparison of considered pure systems ...... 126 Table 6.24: Comparison of considered compressed air + conventional fuel hybrid ...... 127

LIST OF FIGURES Figure 1.1 World’s primary energy supply (data from [2])...... 1 Figure 1.2 GHG emissions by sector in Canada (data from [1])...... 2 Figure 1.3 Different powering options for vehicles...... 4 Figure 1.4 Main types of biofuels categorized by their feedstock...... 5 Figure 1.5 Different types of fuel cells...... 6 Figure 1.6 Different types of batteries...... 7 Figure 1.7 Main subsystems of a pneumatic vehicle including the compression station...... 8 Figure 1.8 Compressor classifications...... 9 Figure 1.9 Main subsystems of EVs and their inter-relation...... 10 Figure 1.10 Main subsystems of the fuel cell vehicle and their inter-relation...... 11 Figure 1.11 EV Energy utilization (data from [2])...... 12 Figure 1.12 Energy utilization on a fuel cell vehicle (data from [3])...... 13 Figure 1.13 Fuel consumption in Canadian transportation sectors (data from [13])...... 14 Figure 1.14 Estimated calculation of GHG emissions of electricity-driven passenger cars (EVs FCVs, and PVs) in Canada (data from [64])...... 15 Figure 3.1 Illustration of a compressed air (CA) vehicle...... 30 Figure 3.2 Schematic of a four-stage compressed air (CA) vehicle...... 31

Figure 3.3 Illustration of a compressed nitrogen vehicle (CN2) ...... 32

Figure 3.4 Schematic of a four-stage compressed nitrogen vehicle (CN2)...... 33

Figure 3.5 Illustration of a liquid nitrogen vehicle (LN2)...... 33

Figure 3.6 Schematic of a four-stage liquid nitrogen vehicle (LN2)...... 34

Figure 3.7 Schematic of four-stage compressed carbon dioxide (CCO2)...... 35

Figure 3.8 Illustration of compressed carbon dioxide (CCO2)...... 35

Figure 3.9 Illustration of compressed air + internal combustion + hydrogen (CA+ICE+H2). . 36

Figure 3.10 Schematic of compressed air + internal combustion + hydrogen (CA+ICE+H2). 37 Figure 3.11 Illustration of internal combustion engine, natural gas and air (CA+ICE+CNG). 37 Figure 3.12 Schematic of internal combustion engine, natural gas and air (CA+ICE+CNG). 38 Figure 3.13 Illustration of internal combustion engine, liquid propane gas and compressed air ...... 38

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Figure 3.14 Schematic of an internal combustion engine, liquid propane gas and compressed air (CA+ICE+LPG) ...... 39 Figure 3.16 Schematic of a compressed air + internal combustion engine (CA+ICE)...... 39 Figure 3.15 Illustration of a compressed air + internal combustion engine (CA+ICE)...... 40 Figure 3.17 Illustration of compressed air + internal combustion engine (CA+ICE) with heat recovery...... 41 Figure 3.18 Illustration of compressed air + internal combustion engine (CA+ICE) with four- stage expansion...... 41 Figure 4.1 Compressed air system with PCM heat exchanger prototype ...... 42 Figure 4.2 Compressed air system with heating element prototype...... 43 Figure 4.3 Hybrid compressed air-electric system prototype...... 43 Figure 4.4 Schematic of compressed air system with heating element system ...... 44 Figure 4.5 Actual Prototype 1 System...... 46 Figure 4.6 Compressed air system with PCM heat exchanger prototype...... 47 Figure 4.7 Actual prototype 2 system ...... 49 Figure 4.8 Hybrid compressed air-electric system prototype...... 50 Figure 4.9 Actual prototype 3 system ...... 52 Figure 6.1 The prototypes manufacturing process showing: (a) Under compressed air system with heating element; (b) Compressed air system with PCM heat exchanger; (c) Above compressed air system with heating element; (d) Hybrid compressed air-electric system...... 78 Figure 6.2 Energy and exergy efficiencies of the components of prototype 1...... 79 Figure 6.3 Exergy destruction rates of major components of the first prototype...... 80 Figure 6.4 Comparison result of experimental and theoretical state point properties of the compressed air system with a heating element...... 82 Figure 6.5 Prototype acceleration 0-100 km/h on the Dynamometer test...... 83 Figure 6.6 Real-time graph of recorded drag force for Prototype 4 tiers on the dyno test. .... 84 Figure 6.7 Prototype dyno graph, torque and power vs. air motor rotational speed...... 85 Figure 6.8 Prototype average tractive effort on the dyno test...... 86 Figure 6.9 Road load force and road load power vs. vehicle speed...... 87 Figure 6.10 Energy and exergy efficiencies of the selected units of Prototype 2...... 88

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Figure 6.11 Exergy destruction rates of major components of Prototype 2...... 89 Figure 6.12 Comparison result of experimental and theoretical state point properties of the compressed air system with a PCM heat exchanger...... 91 Figure 6.13 Temperature distribution of three different PCM and TES materials during a 36 minute period...... 92 Figure 6.14 Torque vs. speed for Prototype 2 air motor on test table...... 93 Figure 6.15 Energy and exergy efficiencies of the selected units of prototype 3...... 94 Figure 6.16 Exergy destruction rates of the major components of prototype 3 ...... 95 Figure 6.17 Effect of ambient temperature on the overall energy and exergy ...... 96 Figure 6.18 Prototype tank depletion time vs. speed...... 98 Figure 6.19 Electric motor current, battery voltage and prototype rear wheel speed during acceleration time...... 99 Figure 6.20 Compressed air vehicle simulation schematic diagram...... 100 Figure 6.21 Produced power vs. driving range ...... 101 Figure 6.22 Work output vs. pressure assuming 300-liter storage tank ...... 102 Figure 6.23 Compressed tank weight change with different pressure and tank capacities .... 102 Figure 6.24 Compressed nitrogen vehicle simulation schematic diagram...... 103 Figure 6.25 Network for the compressed nitrogen and compressed air via pressure ...... 104 Figure 6.26 Liquid nitrogen vehicle simulation...... 105 Figure 6.27 Network output via pressure for the different ambient temperatures...... 105 Figure 6.28 Compressed carbon dioxide vehicle simulation...... 107 Figure 6.29 Driving range vs. work output for different energy consumption per km...... 107 Figure 6.30 Compressed air + internal combustion + hydrogen vehicle simulation...... 108 Figure 6.31 Compressed air + internal combustion engine + compressed natural gas...... 109 Figure 6.32 Compressed air + internal combustion engine + liquid propane gas...... 110 Figure 6.33 Work output and thermal efficiency change for different operating pressures. .. 111 Figure 6.34 Compressed air + internal combustion engine simulation...... 111 Figure 6.35 Compressed air, internal combustion engine with heat recovery system...... 112 Figure 6.36 Compressed air + internal combustion engine simulation ...... 114

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Figure 6.37 The exergy content and ideal maximum driving range of a vehicle operated with compressed ideal gas...... 118 Figure 6.38 Volumetric specific exergy of pressurized air, nitrogen and carbon dioxide. (Note: If not indicated otherwise, the storage temperature is 25oC.) ...... 119 Figure 6.39: Specific exergy of pressurized air, nitrogen and carbon dioxide. (Note: If not indicated otherwise, the storage temperature is 25oC)...... 120 Figure 6.40: Density of pressurized air, nitrogen and carbon dioxide...... 121 Figure 6.41 Specific exergy stored in pressurized carbon dioxide and in compressed air and nitrogen...... 121 Figure 6.42 Work ratio, exergy ratio and exergetic process efficiency of work generation from compressed ideal gas...... 123 Figure 6.43 Overall energy breakthrough for the pneumatic vehicle considering both phases: air compression at charging stations and air expansion on the vehicle. Four-stage compression and expansion. Storage pressure 350 atm...... 123

NOMENCLATURE

A area (m2) COP coefficient of performance D diameter (m) ex specific exergy (kJ/kg) Ė energy rate (kW) Eẋ exergy rate (kW) h specific enthalpy (kJ/kg) Ḣ enthalpy rate, (kW) HHV higher heating value (kJ/kg) ṁ mass flow rate (kg/s) P pressure (kPa) Q̇ heat transfer rate (kW) R gas constant (kJ/kgK) s specific entropy (kJ/kgK) Ṡ Entropy rate (kW/K) T temperature (0C or K) U overall heat transfer coefficient (W/m2K) v specific volume (m3/kg) V volume (m3) V̇ volume flow rate (m3/s) w specific work (kW/kg) Ẇ work rate or power (kW)

Greek Letters η efficiency ρ density (kg/m3) Φ exergy to energy ratio of the fuel γ adiabatic exponent η energy efficiency Δ difference

Subscripts 0 reference state b blade dest destruction elect electrical

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eqv equivalent mech mechanical opt optimum cv control volume d destruction en energy ex exergy exp expander f fuel g generator gen generation ph physical s source 1, 2, ... state numbers

Acronyms AM air motor EES engineering equation solver EV electric vehicle FCV fuel cell vehicle FWA five way valve A FWB five way valve B GDP gross domestic product GHG greenhouse gas HEX heat exchanger HS heat storage OWV one way valve PV pneumatic vehicle PCM phase change material Cp specific heat at constant pressure, J/kgK Cr pressure ratio Cv specific heat at constant volume, J/kgK ER exergy ratio f function h specific enthalpy, J/kg k adiabatic expansion coefficient LHV lower heating value, MJ/kg m Mass, kg N Rotation speed, rpm

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PI Powertrain indicator PR Pressure ratio q Heat, specific, J/kg Q Heat, KJ P Pressure, bar R Universal gas constant s Specific entropy, J/kgK T Temperature, K U Speed, m/s V Volume, m3; or velocity, m/s v Specific volume w Work, specific, kJ/kg W Work, kJ WR Work ratio

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CHAPTER 1: INTRODUCTION

Significant resources are currently being deployed to investigate and engineer electric vehicles in response to environmental, energy and consumer pressures. The transportation sector in Canada is presently based on fossil fuels, which shows large emissions of GHGs. The correlation of a low polluting grid and a highly polluting transportation sector makes realistic and feasible a compressed gas vehicle which, according to the calculations performed as part of this present work, shows fewer emissions than the average Canadian passenger car.

1.1 World energy and environmental outlook

The world’s population and consequent demand for energy is increasing while conventional energy sources are being depleted. In contrast, the increasing reality of global warming and an increase in the earth’s temperature highlight the necessity of a viable and long-term solution for the sustainable development of energy.

Others Biofuels 2% 10% Hydro 3% Nuclear Coal 5% 27%

Natural gas 22% Oil 32%

Figure 1.1 World’s primary energy supply (data from [2]).

As seen in Figure 1.1, a total of 81% of the world’s primary energy is currently supplied from fossil fuels [1], of which 32% belongs to oil, which is still the largest primary fuel for transportation. According to the 2018 energy technology prospective report of the International Energy Agency

(IEA), in order to limit global temperature increase to 2 °C, CO2 emissions related to energy and industrial processes should be decreased by approximately 60%. In late 2019, the government of Canada set an ambitious target to cut greenhouse gas (GHG) emissions by 40% by 2030, and by 80% by 2050, relative to 2018 levels [2].

Agriculture 10% Oil & Gas 26%

Electricity 11%

Building 12% Transportation 24%

Heavy industry Waste & others 10% 7%

Figure 1.2 GHG emissions by sector in Canada (data from [1]).

Fossil fuels, which are still the main source of energy for compensating the growing consumption of energy, bring some concerning problems, as mentioned above. Although some technologies are developed for the more sustainable conversion and consumption of fossil fuels, this strategy is temporary and does not meet the ultimate goals of long-term sustainable development in the context of energy. As a result, sustainable energy using renewable energy sources is to be developed in the source, system, and service sector. As a long-term approach, this form of energy needs to be well established for more efficient and environmentally benign energy systems and reduction in emission. Alternative fuels play an important role in this approach. Sustainable energy production is based on clean and uncontaminated resources. The

main sources of energy for sustainable and clean energy are solar, water, hydro, ocean thermal, tidal, wind, biomass and geothermal. These resources can be used to produce clean energy as well as hydrogen. Renewable electricity now constitutes 25% of the total global power generation [3].

1.2 Transportation Options

As one of the vital sectors, transportation consumes a substantial share from the worldwide energy consumption and produces a significant amount of GHGs. Transportation options are varied nowadays and include: air transportation, represented in passenger and commercial airplanes; water transportation via barges, boats, ships and sailboats; rail transportation by train; and road transportation such as automobiles, buses, trucks, and bicycles. The current study focuses on passenger vehicles.

1.3 Powering Options for Vehicles

Vehicles can be powered via different pathways. Ground vehicles are mostly in need of rotational power for movement. Different possible options for powering vehicles are indicated in Figure 1.3. As an example, fossil fuels are combusted in internal combustion engines (ICEs) for linear movement of a piston inside a cylinder which, in turn, is converted to rotational power in a crankshaft and transmitted to the wheels for driving the vehicle. ICEs can also be fueled by new environmentally friendly fuels as biofuels, such as bio-ethanol. Fueling ICEs with carbon-free fuels such as ammonia and hydrogen is also a possible and promising way to power vehicles. Electric options represented in the utilization of fuel cells is one of the encouraging options to power vehicles, in addition to batteries. In the case of electric vehicles, the challenge is mainly where the power demand is maximum. For this case, new generations of carbon-based materials as super capacitors, which can store a significant amount of energy and discharge it in a short time, are being developed. Electric power can be supplied from some renewable fuels or from electricity via batteries or fuel cells. This harnessed power can be used to drive the vehicle or even re-charge the battery when needed [4].

Powering options

Internal Electric Fuel Cell Pneumatic Combustion Vehicles Vehicles Vehicles Engine (ICE) (EVs) (FCVs) (PVs) Vehicles Figure 1.3 Different powering options for vehicles.

1.4 Conventional Fuels

Conventional fuels, known as fossil fuels, are the hydrocarbons made from the remnants of the carbon-containing living organisms buried under the earth’s crust layers. Time, pressure and heat have significant influence on the constitution of fossil fuels, which can be formed in three major types, namely coal, natural gas, and oil. Fossil fuels power vehicles via a combustion process that produces high pressure and high temperature gases to provide linear power in cylinders and rotational power via crankshafts. Major types of fossil fuels used in vehicles to date are petroleum, such as gasoline, diesel, jet fuel and liquefied petroleum gas (LPG), and natural gas in the form of compressed natural gas (CNG) and liquefied natural gas (LNG). The main challenge of using conventional fuels has been reported as the knocking effect in ICEs, NOx and Sox emissions as outcomes of combustion.

1.5 Renewable Fuels

Renewable fuels are basically the fuels made from renewable sources that can be constantly replenished by nature. The main renewable materials for this kind of fuel are biomass and water, which can be found in nature. Biomass is the main source of biofuels such as bioethanol, biodiesel and also hydrogen-rich gas (syngas) while water is the main source for hydrogen production as a carbon-free fuel. Some fuels can be produced as a secondary product of renewable sources, including ammonia which is also a carbon-free fuel. In addition, renewable energy sources are constantly reproduced on a human life timescale, such as solar, wind, sunlight, tides, and geothermal heat. Renewable energy can be a promising alternative for fossil fuels in many different areas such as EVs, ICEs, power plants, and thermal applications. Biofuel

is a liquid fuel composed of mono-alkyl esters of long-chain fatty acids obtained from bio-based materials such as animal fats or lignocellulose biomass. The common types of biofuels are bioethanol bio methanol, biogas, syngas, biodiesel and bio-hydrogen. The application of biofuels, which results in lower emission and carbon footprint in their life cycle, is considered as being safe and clean for the energy and transportation sector. As seen in Fig.1.4, biofuels are basically categorized in four generations based on the feedstock of which they are made.

Figure 1.4 Main types of biofuels categorized by their feedstock.

The first generation of biofuels is made from edible food crops such as canola, corn, wheat, and straw. The second generation of biofuels consists of those made of lignocellulose biomass as agricultural or municipal solid waste, which have a lignocellulose structure. The term lignocellulose means that they have been constituted via the integration of biopolymers of lignin, cellulose, and hemicellulose [4]. The main problem of second-generation, and especially agricultural, waste is the conflict of its production with the food chain. However, the second generation of biofuels can be directly used in diesel engines or added to gasoline as an additive for better combustion while avoiding NOx. The third generation of biofuels is composed of fuels that are made of algal biomass, such as microalgae and macro algae. Algae has the advantage of less need of water for growth as well as non-involvement in the food chain. However, the volatile matter of algae is less than agricultural waste and usually gains less yield of biofuel. While defined in different ways in the literature, Lu, Sheahan and Fu [5] defined the fourth generation of biofuels as a product of metabolic engineering of algae for producing biofuels from oxygenic photosynthetic organisms.

In addition to biomass, solar energy is one of the most important renewable energy sources on earth. Solar energy generation involves the utilization of the sun's energy to afford 5

hot water via solar thermal systems or electricity via solar photovoltaics, which is commonly used in vehicular applications. Photovoltaic cells are devices that convert sunlight or solar energy into direct current electricity. The main part of a PV system is the PV cell, which is a semiconductor device that changes solar energy into direct current electricity.

1.6 Electric Options

The concept of EVs, which have been developed in the last two decades, is to convert electrical energy into mechanical energy and provide rotational power for the vehicle. The electrical energy can be supplied through storage options such as batteries or super capacitors. Moreover, fuel cells that convert fuels into electricity can be an intermediate step to avoid the storage of electricity by instead using fuels such as hydrogen. The only product of hydrogen-fueled fuel cells is water and electricity, which makes them entirely zero-emission and environmentally friendly.

Fuel cells

Proton Solid exchange Direct Alkaline Phosphoric Molten Ammonia Methanol (AFC) Acid Oxide Carbonate Fuel Cells membrane (DMFC) (PAFC) (SOFC) (MCFC) (AmFC) (PEMFC)

Figure 1.5 Different types of fuel cells.

Fuel cells work based on the electrochemical conversion of materials into electricity. The different types of fuel cells are presented in Fig. 1.5. Proton exchange membrane (PEM), which converts hydrogen into electricity and water, is the common type of fuel cell used for EVs. Fuel cells can provide much higher efficiency compared to fossil fuels and ICE engines. However, the challenge is mainly due to the low power output compared to that of ICE. Fuel cells can be categorized by their electrolyte materials, operating temperature, type of ions that can be transferred via the electrolyte, and the types of reactants that are used. The common types of fuel cells can be illustrated as follows: Another electrochemical device for supplying electricity for EVs is the battery. A battery is basically made of a pack of cells packed together.

The cells are made of positive and negative electrodes connected via an electrolyte. The output of batteries as DC electricity can be transformed through convertors in EVs to AC where needed [6]. An electric battery is a device comprising two or more electrochemical cells that have the ability to change the stored chemical energy into electrical energy. Batteries are used in EVs to supply the electric power to the electric motor and to store the excess electricity that can be recovered through any additional installed part in the vehicles, such as the dynamo. The numerous types of batteries that can be utilized in EVs can be itemized as follows:

Batteries

Lead Nickel- Metal Sodium- Lithium- Cadmiu acid based air based ion m-base

Figure 1.6 Different types of batteries.

Super capacitors can assist batteries in powering EVs. They are characterized by their rapid charging and discharging time, which can reach a few seconds, and they can endure many charging and discharging cycles. Thus, they can be efficiently used to capture the electric energy recovered from the wasted kinetic energy during parking and supply it to the vehicle powering system during the transition phases, such as acceleration, where the electric power supply is required in a short time. This action can reduce both fuel utilization and harmful gas emissions during vehicle operation [7].

1.7 Compressed Air

Because of simple and safe production and easy handling, compressed air is widely used by industries and also by energy sectors worldwide. However, the production of compressed air is energy-intensive, such that it accounts for approximately 10% of the power consumption of the industry sector in the European Union. Some improvements are proven to save a significant

amount of energy. As an example, some of these improvements include leak detection and sealing, demand and supply synchronization, and use of the full capacity of compressors.

Atmospheric air Pneumatic Grid electricity or Air Power Compressed vehicle electricity from compression air storage renewables station

Heat Reheating system Compressed (heat exchange air motors

Compression Heat recovery with ambient Heat station site unit air)

Mechanical energy for propulsion

Figure 1.7 Main subsystems of a pneumatic vehicle including the compression station.

In this section, the pneumatic vehicle (PV) is analyzed on the basis of the first and second laws of thermodynamics. The system under consideration is presented in Figure 1.6 and includes both the compression station and the vehicle. Basically, the grid electricity or electricity generated from renewable/sustainable sources is used to compress the atmospheric air to high pressure and high density [8]. For better efficiency, the compression process can be conducted with heat recovery. The compressed air is charged on the vehicle tank where it serves for propulsion. Pneumatic motors or motor systems are used for transforming the thermo- mechanical energy of the compressed air into mechanical energy. Air reheating during expansion and the multistage expansion process can be applied for better efficiency. There are many different types of compressors on the market, each using different technology to produce air. A description of the compressors commonly used in the industry follows in xx and their characteristics are summarized in Figure 1.7. Compressed air is clean, readily available, and simple to use. Thus, many industrial applications use compressed air, including: to provide

cooling, aspirating, agitating, or mixing; to inflate packaging in an air conditioner unit; to clean parts or remove debris; and to lower pressure compressed air for blowguns, air lances, and agitation.

Figure 1.8 Compressor classifications.

In a mining machine where electric motors or combustion engines cannot be used because of the risk of fire due to the presence of inflammable fumes and gases, compressed air power is a paramount utility in running mining equipment. Compressed air is used in the processing of food and farm maintenance in the spraying of insecticides [9]. The use of compressed air in practically all types of construction, including digging holes for bridge foundations, building dam structures, and sewage and tunnel work, produces better and faster results. Air operated drills, wrenches and riveting hammers are used for completing various tasks in the aircraft industry. Compressed air is the most useful commodity because it can be stored and used as required. The production cost is less compared to others. For neat and clean forms of energy in every industry, compressed air is a common utility. 1.8 Electric and Hybrid Electric Vehicles

Considering the issues faced by the transportation sector in recent years, a sustainable vehicle is expected to be environmentally friendly, cost-effective, and technically and energetically efficient Alternative energy carriers are an alternative to conventional ones. Hence, sustainable vehicles can be categorized in terms of their energy supply. Electricity is one of the applicable sources while the storage of electricity remains one of the main challenges. For cleaner transportation, hydrogen and some alternative fuels such as biofuels can also be good alternative candidates to gasoline.

Grid electricity or Power Electronics Electric Auxiliary electricity from and rectifier battery electric renewables systems on vehicle

Heat (lights, heating etc.) Battery Heat rejection Electric Charging System motor Station (cooling)

Mechanical energy for propulsion Electric Vehicle

Figure 1.9 Main subsystems of EVs and their inter-relation.

However, the cost of production, storage, and their corresponding power generation technology are to be taken into account. Compressed air is also one of the promising options for avoiding the high cost of production (in the case of alternative fuels) and carbon emissions (in the case of gasoline). Researchers have studied sustainable energy options for vehicles, some of which have been developed and industrialized by some companies. The most common types of alternative vehicles in single fueled or hybrid form can be listed as follows:

 Hybrid hydraulic vehicles (HYHVs)  Pneumatic hybrid vehicles (PHVs)  Electrical energy storage-based vehicles (e.g. flywheels or super capacitors)  Battery electric vehicle (BEVs)  Fuel cell vehicles (FCVs)  Plug-in hybrid electric vehicles (PHEVs)  Hybrid electric vehicle (HEVs) The basic operational diagram for the EV process is presented in Figure 1.8, which shows the main energy conversion subsystems that work on the vehicle and at the charging station [10]. Essentially, the grid system or power generators that derive electrical energy from renewable 10

sources are used to charge the electric battery of the vehicle; in this respect, rectifiers or other electronic components (e.g., inverters) are employed at the battery charging station. On the vehicle, the energy stored in the battery is mainly used to drive the electric motor but, in a much lower measure, it supplies other auxiliary vehicle systems.

Hydrogen production system Electric Mechanical Water motor energy for propulsion Grid electricity or Power Electrolysis electricity from unit renewables Fuel cell system Heat Hydrogen recovery System for cabin

Heat Rejection heating Hydrogen Mechanical compression energy for unit propulsion Fuel cell Vehicle

Figure 1.10 Main subsystems of the fuel cell vehicle and their inter-relation.

The electric motor develops mechanical energy that is available at its shaft. The transmission subsystem transforms the mechanical energy to kilometres driven. The fuel cell vehicle (FCV) system diagram is introduced in Figure 1.9. In this case, grid electricity is used to generate hydrogen from water electrolysis; also, electricity is used to compress the hydrogen up to a storable pressure in the gas phase, which is about 350 bar [11]. The hydrogen is then charged to the vehicle storage tank where it is further used to supply a fuel cell system. The fuel cell supplies electricity to the electric motor for propulsion. Also, some electricity is used for other important purposes on board the vehicle. The heat rejected by the fuel cell is partially recovered and used for cabin heating, if needed. Because of the considerably large portion of GHG emission by transportation in developed and developing countries, the advancement of EV vehicles and hybrid types (EVs and HEVs) is one of the crucial steps toward sustainable transportation and a cleaner environment. In general, the term “hybrid” in the automotive context refers to vehicles that work based on propulsion systems that enable them to switch between two or more fuel options. 11

In terms of fuel economy, environmental pollution, and vehicle efficiency, there are some priorities in using a hybrid vehicle. EVs are being developed and improved in many departments, including design, fuel technology, and control and charging, which marks them as successful candidates for replacing ICE vehicles.

Electric rectifier loses, 5% Heat dissipation durnig charging, 5% Battery self discharging loses, 10%

Onboard electric loses, 1%

Available shaft Onboard electric uses, energy, 56% 4%

Electric motor loses, 19%

Figure 1.11 EV Energy utilization (data from [2]).

The energy supplied, as input to the EV, is the same as the electricity consumed to charge the battery. The energy breakthrough of the EV is shown in Figure 1.10. The main losses that characterize the EV are: electric rectifier loss; heat dissipation at the battery charging; battery self-discharge loss; on-board electric loss; and electric motor loss. The remaining electric energy is used for two purposes, namely to supply the electric motor and to power various electrical equipment that is needed on board the vehicle [12]. It can be seen that, from the 100% electrical energy supplied to the system, 40% is lost in various ways. About 4% is used on board for purposes other than propulsion, while the mechanical energy generated by the motor shaft represents 56% from the initial energy input. The energy losses at various stages characterizing the FCV operation are indicated in Figure 1.11.

Available shaft Electrolysis work, 24% loses, 23%

Electric motor loses, 5% Compresion Onboard electric loses, 7% uses, 5%

Onboard electric Fuel cell loses, loses, 1% 35%

Figure 1.12 Energy utilization on a fuel cell vehicle (data from [3]).

1.9 Sustainable Energy, Vehicles and GHG Emissions

In Canada, where there are about 19.5 million registered road vehicles, 96.1% are below 4.5 t curb mass, 2.3% are light trucks of 4.5-15t while heavy trucks with a curb mass of over 15 t account for the remaining 1.6%. The major fuel for road vehicles in Canada is gasoline, as indicated in Figure 1.12, which shows the share of transportation fuels per type for the entire transportation sector. The yearly distance traveled by passenger cars, buses and light trucks (curb mass below 4.5 t) is about 300 billion km. A major use of passenger transport vehicles is for “going to work”. In Canada, people go to work by public transport (11%), by their own car (72%) or by other means, such as cycling or walking. It should be noted that the total Canadian workforce is around 16 million people. Also worthy of note is that, from the total GHG emission of a household, 63% is due to private vehicle use. The majority of passenger car GHG emissions, namely 35%, is sourced from vehicles owned by low/middle-income families, which account for 31% of Canadian households [13].

The electricity-to-shaft efficiency for EVs, FCVs, and pneumatic vehicles (PVs) allows for the calculation of the electrical energy needed in each case to produce a unit of energy at the vehicle shaft. The actual data for GHG emissions in Canada and its provinces, as shown in

Figure 6.6, are used to calculate the results presented in Figure 6.7. Basically, the gram of CO2

equivalent generated by the grid for each kWh of electricity has been divided by the electric-to- shaft efficiency of the vehicle, which represents the kWh of mechanical energy at shaft over the kWh of electricity input.

Heavy Fuel Oil Diesel Fuel Oil 3% Propane 32% Aviation Turbo Fuel 0.49% 10%

Other 1%

Electricity Aviation Gasoline 0.09% Motor Gasoline 0.12% 54% Natural Gas 0.15%

Figure 1.13 Fuel consumption in Canadian transportation sectors (data from [13]). In Figure 1.14, the dash-dot line indicates the actual average emission of Canadian passenger cars. It can be concluded from this result that all three considered kinds of grid- connected EVs bring benefits with respect to GHG emissions in comparison with gasoline cars in Canadian provinces (as average), with the exception of Alberta, Nova Scotia and Saskatchewan. Figure 6.7 also indicates the GHG emissions of electricity-driven vehicles in the case where renewable energy sources are used to generate electricity. According to the work of

Dincer, Rosen and Zamfirescu [14], an indicator of 5.11 g CO2eqv per kWh electricity is used in calculations. It also appears justifiable to develop power stations based on renewable energy sources for fuelling proximity vehicles with a clean energy carrier. Each vehicle propulsion solution (EV, FCV, and PV) has its advantages and drawbacks. As an example, the electric battery of the EV is voluminous and heavy. The compressed air tank is also voluminous but less heavy than electric batteries for the same usable energy. Compressed hydrogen tanks are the lightest but are still voluminous and also present explosion danger. It

can be said that the three solutions complement each other rather than compete. Hybrid vehicles, such as the pneumatic-hydrogen or pneumatic electric, also appear to be a possible solution for clean transportation. In addition, the gasoline-pneumatic hybrid can be seen as an alternative to gasoline-electric vehicles featuring low GHG emissions [15].

10000 Canadian passenger cars: 943 gCO /kWh 2eqv Mech FCV EV PV

1000

Mech 100

/kWh 2eqv

10 gCO

Figure 1.14 Estimated calculation of GHG emissions of electricity-driven passenger cars (EVs FCVs, and PVs) in Canada (data from [64]).

1.10 Motivation

Achieving sustainability in the transportation area would reduce the negative environmental impact of the transportation sector represented in greenhouse gas emissions. Also, it will reduce the dependence on fossil fuels. Therefore, the solution to achieve better sustainability is to use clean sources of fuel to power the vehicles and to develop efficient systems for vehicle propulsion. Many solutions are suggested like using solar energy, fuel cells, renewable fuels, batteries, etc. What current research focus on is integrating, Electric, pneumatic and solar energy powering options together which will provide realistic sustainable solution and higher efficiencies for the vehicle operating system. Achieving sustainability in transportation area would reduce both greenhouse gas emissions and energy consumption. Transportation offers a 15

spectrum of costs and level of services, which results in substantial differences across the world. The price of a transport service does not only include the direct out-of-the-pocket money costs to the user but also includes time costs and costs related to possible inefficiencies, discomfort, and risk. However, economic actors often base their choice of transport mode or route on only part of the total transport price.

1.11 Objectives

The goal of this thesis is to show conceptual development, analyze, performance assessment, comparative evaluation to further develop a pre-commercial design of compressed air vehicle and to build prototype of systems. Detail objectives are itemized as below:

 To develop and explore the thermodynamic limits and proposing conceptual solutions for using air expansion for vehicle applications, then enhance energy consumption and improving overall performance of the proposed pneumatic/hybrid vehicles by developing an aerodynamic numerical modeling by identify and discuss potential improvements, this will result from proposing innovative adaptations of the key components, contribution to the overall system and its integration in other systems.

 To design innovative pneumatic and hybrid vehicles systems with different powering options by considering the comprehensive thermodynamic modeling of the proposed integrated systems and applying thermal storage systems with different phase change materials (PCM) on-board for high and low temperature storage depending on the season, due to necessity to design an efficient and clean air compression refuelling station operated by renewable energy sources.

 To analyze systems energetically and exergetically with determining the flow energy and exergy for each stream in the system, Identify exergy destruction rate, energy losses for each component and calculating the energy and exergy efficiencies then assess the systems through complete parametric studies with identify the influence of changing environmental conditions on the performance evaluation of each system studied, investigate the effect of varying different design and operating parameters on the systems performance.

 To build an actual prototype for testing purposes and carry out the performance measurements analyses for the proposed prototypes in the Automotive Center of Excellence (ACE).

1.12 Novelties

Three novel compressed air powering option prototypes are developed, analysed, built and tested. Ten novel systems configurations are developed and analysed using energy and exergy analysis approaches. It is the first-time compressed air vehicle with 4 air motors developed, analysed, built and tested. Compressed Air system with 4 stage expansions developed and analysed. Compressed Nitrogen, Liquid Nitrogen, and Compressed Carbon Dioxide energy systems are developed and analysed and compared. Novel integration between Compressed Air and Internal Combustion with three different fuels including Hydrogen, Natural Gas and Liquid Propane successfully investigated. The source of energy in a compressed air vehicle is the high- pressure compressed air tank, compressed air derives its energy from the thermodynamic work done by an expanding gas. This research advances a solution towards the reduction of greenhouse gas (GHG) emissions in the conveyance sector. In essence, one proposes to utilize the subsisting infrastructure of electricity generation and distribution to engender a zero- emitting energy carrier for conveyance sector - which is compressed air. Compressed air transportation appears to be a promising solution for zero-emitting proximity transportation.

CHAPTER 2: LITERATURE REVIEW

Increasing energy demand with world population growth and development, and the environmental consequences of excessive fossil fuel consumption to meet this demand, are primary factors behind global initiatives for the implementation of more environmentally benign energy options. Sustainable development of alternative energy options requires both short and long-term solutions in order to reduce fossil fuel dependence, and mitigate the negative environmental impacts resulting from their use. In this chapter, the different powering option for passenger vehicles will be discussed, and the primary research reported in the area of vehicle propulsion will be highlighted.

2.1 Experimental compressed gas and hybrid vehicles

Three-wheeled vehicles, which occupy less space compared to four-wheelers, have been designed in order to reduce weight [16]. Unlike conventional transmission systems that include a clutch, countershaft, flywheel, propeller shaft, and differential, the pneumatic motor is connected and coupled to the rear wheel with the use of an intermediate gearbox reducing both transmission losses and the weight of the vehicle. However, in-depth research is required to completely prove this technology for its commercial as well as technical viability. Verma [17] briefly summarizes the principle of technology, as well as the latest developments, advantages, and problems in using compressed air as a source of energy to run vehicles. Compressed air for vehicle propulsion has already being explored. At present, air-powered vehicles are mostly being developed as a more fuel-efficient means of transportation. Two-stroke engine technologies are compared with four-stroke engines in [18], whereby the researchers took a four-stroke petrol engine and, with some modifications, made it into a two-stroke air engine. The engine camshaft rotates once for every two rotations of the flywheel. For a two-stroke, it needs one rotation of the camshaft for a rotation of the flywheel, for which there must be an opening of both inlet and exhaust valves. In a later study, Verma [19] introduced the latest developments of a compressed-air vehicle along with an introduction to various problems associated with the technology and their solution. Compressed air, as a source

of energy in different uses in general and as a non-polluting fuel in compressed air vehicles, has attracted scientists and engineers for centuries. The effective application of pneumatic power is advanced in [20]. PVs, which have replaced the battery-operated vehicles used in industries, require very little time for refueling compared to battery-operated vehicles. In general, the technology simply involves modifying the engine of any regular ICE vehicle into an Air Powered Engine. An experimental analysis to develop a hybrid pneumatic vehicle that works on compressed air is proposed in [21]. The vehicle is powered by a compressed-air engine and can be later switched to batteries. The vehicle uses a non-renewable and pollution-free fuel. A PV is a pneumatic actuator that creates useful work by expanding compressed air. When this compressed air expands, the energy is released to do work. Hence, this energy in compressed air can also be utilized to displace a piston. Szabłowskia and Milewskia [22] introduced a dynamic analysis of the compressed air energy storage in a car. The analysis was used to determine those processes most relevant to achieving the highest possible efficiency. A state of the art review is also presented. Simple technical-economic analysis of using this kind of car is also performed and discussed by taking local Polish conditions from an electricity market. The main advantages, as well as drawbacks of the compressed air cars, are indicated. Huang et al. [23] presented the experimental study results concerning the operating capabilities of the HPPS and the effect of the contraction of the cross-sectional area (CSA) at the merging region of the energy merger pipe for the change in the compressed air flow pressure (Pair) on the exhaust-gas energy recycling of the HPPS. The experiments were performed on an HPPS that uses an innovative energy merger pipe with a total length of 530 mm, a diameter of 34 mm, and an angle between the two pipes of 301. The CSA was adjusted for the change in Pair. The experimental results show that the exhaust-gas energy recycling and the merger flow energy are significantly dependent on the CSA adjustment for the change in Pair. The optimum conditions for the best merging process can be achieved at a CSA of around 5–35% in the full range of Pair. Under these conditions, the exhaust-gas energy recycling efficiency reached approximately 75–81%. Therefore, a vehicle equipped with an HPPS can achieve an efficiency that is approximately 40% higher than that of conventional vehicles.

The researchers in Ref. [24] presented a novel design for a pneumatic re-generation system hybrid in an electric car. Firstly, in order to increase the life of the battery, the battery is not recharged while the car is running, but only charged by the main power in the garage. This is known as a plug-in electric car. Secondly, the energy from the car’s deceleration will be captured by a special gearbox and stored in the compressed air tanks. Thirdly, the energy stored will drive an air motor to supply supplemental power. Since this chain is a mechanical energy transformation, in theory, efficiency is higher than a typical hybrid car. The experiment seemed to obtain a satisfactory result.

The researchers in Ref. [25] built a power system for a new kind of air-powered vehicle using an HP transformer as the pneumatic pressure boosting the structure and a hydraulic motor as the power unit. This became the foundation for the optimization of the power system. The dynamic characteristics were analyzed by building a mathematic model and setting up an experimental station. Moreover, the effect of several key structure parameters was researched. Through experimental and simulation study, it can first be concluded that the mathematical model is proved to be effective. Secondly, increasing the area ratio of the pistons would improve the output power as well as reduce the system efficiency. For this study, the authors chose six xx for a balanced choice. Thirdly, the output power and the system efficiency will rise with a larger oil discharge orifice. Finally, the increasing pressure of the input air will raise the power and meanwhile decrease the efficiency. In this system, the efficiency will remain above 30%. This research can be referred to in the design of the power system of air-powered vehicles and the study on the optimization of the dynamic characteristics.

2.2 Compressed/liquid gas vehicles

The modeling and analysis of air consumption in a pneumatic system of a compressed air- powered vehicle is presented in [26]. A mathematical model of the pneumatic system was developed and analyzed during simulation studies and compared with experimental data that was logged on the prepared test rig. The performed analysis and presented results help to determine the efficiency of the pneumatic system in the compressed air car. Shen and Hwang [27] developed a model pneumatic hybrid motorcycle system and simulated its acceleration and mileage (km/L) performance. A novel engine design for a pneumatic hybrid motorcycle is

presented. The results show that a pneumatic hybrid motorcycle can improve efficiency. Compared with previous pneumatic hybrid engines, the design in [26] does not need features such as extra air motors, compressors, or mixing chambers. Liu and Yu [28] investigated the feasibility and outlook of air-powered vehicles, including compressed air-powered and liquid nitrogen-powered vehicles. The thermodynamic analysis and experimental data were used to investigate aspects such as the energy density, performance, safety, running efficiency, fuel circulation economy and consumer acceptance. The results show that: compressed air and liquid nitrogen have similar energy density as a Ni- H battery; the characteristics of an air-powered engine are suitable for driving a vehicle; the circulation efficiency of liquid nitrogen is 3.6%–14% and that of compressed air is 25%–32.3% in practice; and existing technology can assure its safety. It is concluded that although the performance of an air-powered engine is inferior to that of the traditional inert combustion engine, an air-powered vehicle is fit for future green cars to realize the sustainable development of society and the environment. The work of Sharma and Singh [29] aimed to analyze the different effects of various parameters on the air engine, including: air pressure from the compressor; capacity of the compressor tank; the number of strokes of the engine, cylinders, storage tanks, and inlet and exhaust ports; pneumatic guns; and use of electrical devices such as a piezometer and solenoid valves. A review of this work identified that an engine speed of 3000 rpm was obtained at a maximum pressure of 8 bar. Furthermore, a high power gain of about 0.95 kW was achieved at 9 bar and 1320 rpm. At a small pressure of 10 bar with a varying injection angle from 10° before the top dead center to 15° after the top dead center, the rotating speed was found to be 715 rpm to 965 rpm whereas, at a higher pressure of 25 bar with varying injection angle, the speed ranged from 1191 rpm to 1422 rpm. At a lower pressure of 5 bar, the maximum speed was 28.9 km/h with a traveling distance of 2.5 km, whereas at a high pressure of 9 bar, the maximum speed attained was 36.5 km/h traveling 1.7 km. Addala and Gangada [30] observed that an air car propelled with a compressed air motor or a pneumatic wrench hold compressed air to about 11.3 bar pressure. The process flow was compressor reciprocating compressor-single stage- hermetically sealed-1, 5 HP, 3000 rpm. A rotary vane motor performed satisfactorily in high- temperature areas up to 93°C and air stored in a tank at 11.03 bar pressure. A compressed air

engine was reformed in [31] from a four-stroke engine to a two-stroke engine using cam gear and crankshaft modifications. A power of 0.95 kW was achieved at 9 bar and 1320 rpm. At the same pressure, a maximum torque of 9.99 Nm was obtained at 465 rpm. Due to the improved cam gear system, the inlet valve opened at 0° crank angle and closed at 150° crank angle, and the exhaust valve opened at 170° and closed at 360°. Baig and Husain [32] studied a 100cc ICE that was modified to an air compressed engine. The engine was improved from a four-stroke to a two-stroke engine. An engine speed of 3000 rpm was obtained at a maximum pressure of 8 bar and a temperature of 15ºC. Three different experiments were conducted in [33] by using a vane-type turbine as a prime mover with different casing diameters of 50 mm, 100 mm, 150 m, at 2500 rpm speed, 6 bar air pressure and 60º of constant injection angle. This experiment showed that optimum shaft power of the turbine was obtained when the ratio of rotor diameter to casing diameter was 0.70 to 0.75 and the vane angle was 30-45º. Hence, the efficiency of the light vehicle would be around 75-97%. In [34], an experiment was performed with a vane-type novel air turbine that was used to run a motorbike. A 300 psi air compressor was used to make an impact on the vanes of the turbine and power of 6.50 to 7.20 HP was gained at an initial speed of 500 to 750 rpm at 4-6 bar air pressure to the running speed of 2000 to 3000 rpm at 2 to 3 bar pressure. It was observed that the efficiency of the turbine varied from 72 to 97%.

2.3 Compressed gas and combustion engine hybrid vehicles

The design of a highly efficient pneumatic motor system is presented in [35]. The air engine is currently the most generally used device for converting the potential energy of compressed air into mechanical energy. However, the efficiency of air engine is too low to provide sufficient operating range for the vehicle. In this study, the energy contained in compressed air/pressurized hydraulic oil is transformed by a hydraulic motor to mechanical energy in order to enhance the efficiency of using air power. To evaluate the theoretical efficiency, the principle of balance of energy is applied. The theoretical efficiency of converting air into hydraulic energy is found to be a function of pressure; thus, the maximum converting efficiency can be determined. To confirm the theoretical evaluation, a prototype of a pneumatic hydraulic system was built. The experiment verifies that the theoretical evaluation of the system efficiency is

reasonable and that the layout of the system is determined by the results of the theoretical evaluation. A systematic optimization of the operation of such an engine system is introduced in [36], where both two-stroke and four-stroke modes are analyzed. The optimized valve and throttle actuation laws for all modes and operating areas lead to generic maps that are independent of the engine size. Thus far, the pneumatic hybridization of ICEs was thought to require a two-stroke operation. This paper presents a novel hybrid pneumatic engine configuration that entails fixed camshafts for both intake and exhaust valves while utilizing variable valve actuation for one charge valve per cylinder only. This configuration is operated entirely in four-stroke modes. Such a configuration requires careful optimization of its operating strategy to achieve its fuel economy potential. Compared with a full two-stroke operation, only small efficiency losses result from using four-stroke modes with these new operating strategies. Initial measurement results with such an engine system are presented in this paper to confirm the validity of the principles of operation. A system that replaces the battery’s electric-chemical energy with flow work and optimizes the management and utilization of the energy is proposed in [37]. This power system is able to keep the ICE working at its optimal condition and turn its waste energy into effective mechanical energy, thus enhancing the thermal efficiency of the entire system. Using computer simulation software ITI-SIM, this study simulates the overall dynamic characteristics of the system in accordance with the regulated running-vehicle test-mode ECE47 and, with experimental verification and analysis, proves that this system can meet the requirements of the standard running-car mode. As for recycling waste energy, the experimental results show that this design could offset the shortcomings of the low density of pneumatic power and so effectively enhance the efficiency of the entire system. Working performance for a four-stroke piston-type compressed air engine (CAE), via experimental research, is investigated in [38]. An ICE is modified to a four-stroke CAE and a mathematical model is set up. Working performances are investigated by output torque, power, air consumption, exhaust pressure, exhaust temperature and cylinder pressure on a test bench. The CAE is installed on a vehicle for the road test. The experiment and analysis show several meaningful results. The increase of the supply pressure will result in an increase in the rotational speed, which can effectively improve the output torque and power. However, it can lead to an increase in air consumption.

The success of this application demonstrates compressed air cars are likely to be industrialized duo to their zero pollution and zero emissions. From among many possible configurations, a particular air hybridization design in introduced in [39]. The engine cycles are enabled by a highly flexible engine valve train, which actuates engine valves to generate the desired torque with optimal efficiency. A lumped parameter model is first developed to investigate the cylinder tank mass and energy interaction based on thermodynamic relationships and engine piston kinematics. Special consideration is given to the engine valve timing and air flow. A high fidelity, detailed model, using the commercially available GT-Power software, is developed for a commercial 10.8-liter heavy- duty diesel engine with a 280-liter air tank in order to capture such effects as engine friction, heat transfer, and gas dynamics. The model is used to develop optimal valve timing for engine control. The established engine maps are incorporated into the ADVISOR vehicle simulation package in order to evaluate the potential fuel economy improvement for a refuse truck under a variety of driving cycles. Depending on the particular driving cycle, the simulation has shown a potential 4-18% fuel economy improvement over a truck equipped with a conventional baseline diesel engine.

2.4 Compressed gas and electric hybrid vehicles

Two different configurations of using a multi-stage air-powered engine with variable valve timing for powering a light transport vehicle were evaluated through thermodynamic simulation in [40]. The expanded cold air between the stages was used to refrigerate the cold space and thereby be reheated. However, this method cannot completely meet the refrigeration load. Thus, in the first configuration, the air engine provided the shaft power for propulsion and for additional refrigeration. In the second configuration, the air engine was connected in parallel to a motor/generator and Li-ion battery. The total refrigeration load was met by the expanded cold air between stages. The additional shaft power available was used to charge the battery. After depletion of the compressed air, the battery was used to provide shaft power and refrigeration. The range of the hybrid configuration was evaluated to be slightly higher. A comprehensive review of the compressed-air hybrid technology in a passenger and commercial vehicle, since the beginning of its discovery to date, is presented in [41]. Hybrid

technology has become popular in the automotive industry since the technology is proven to offer improved vehicle efficiency, fuel savings and a greener environment. The well-known hybrid technology is hybrid-electric. Nevertheless, the price of the hybrid-electric automobile is high, the arrangement is complex, and it is not completely green. These disadvantages have triggered innovation in a hybrid technology, known as compressed-air hybrid technology, which uses a combination of ICE and fluid power components as a propulsion unit and compressed-air energy as a power source. The energy is stored in a tank/accumulator. Once the energy in the storage is low, the system utilizes energy losses in braking which it recovers into useful energy. This study also concentrates on the hybrid compressed-air design, components, latest findings, technology breakthrough, and benefits and drawbacks of the system. Further, the review encompasses the most recent prototype that has been tested. Based on the study, the literature shows that the compressed-air hybrid system is proven to work. Nevertheless, further research needs to be extended to resolve some issues that include amending the energy capability and lightweight system design. The two-sub-system is promising, but nevertheless far from the point of commercialization. However, the three-subsystem is proven to save energy and reduce fuel consumption. Although it still needs to be further refined, it has a considerable potential for introduction into the market. Since compressed-air hybrid technology in a passenger car is still new, there is a significant scope for exploration. If it is successful, hybrid compressed-air technology will clearly benefit the future in the aspects of energy efficiency, cost-saving, and reduced pollution.

2.5 Comparative study of hybrid vehicles

Three conceptual pneumatic and hybrid integrated systems for vehicle applications, along with comprehensive parametric studies for all systems, are developed in [42]. Furthermore, two patents, entitled “A pneumatic power and drag system” and “A hybrid pneumatic power and drag system”, have been published in the US patent office. A PV with a chassis, wheels, a compressed air tank, and an air motor driven by compressed air and connected to a wheel is provided in [43]. The vehicle also has a ventilation system for the passenger compartment. The work in [44] describes a car designed with a compressed air propulsion system that supplies air

utilized by a pair of opposing cylinders and their associated pistons and push/pull rods to cause a pair of sprockets to rotate clockwise in a controlled manner. Meanwhile, a micro-power pack that utilizes automotive alternators operated by a micro-gas turbine to recharge battery packs for EV application is developed in [45]. Micro gas turbine efficiency is obtained via thermodynamic analysis of a simple Brayton cycle. The performance of the gas turbine is investigated through a series of experiments at loading and no loading conditions. The results show an upsurge in the mass and volumetric densities by four and five times, respectively. The design, fabrication and the first- round test of a 373 kW hybrid electric vehicle using a two-spool, intercooler gas turbine engine with integral induction type alternators, at which the gas turbine functions as the prime source of power for the vehicle, is reported in [46]. Theoretical and experimental analyses for a novel hybrid system, utilizing a gas turbine instead of an ICE, is conducted in [47]. The system consists of a 100 kW battery pack and two turbo gas sets of 5 and 16 kW. The results show that the proposed system has all the potential to compete with both conventional ICE and fuel cell- powered vehicles. The thermodynamic efﬁciency of a compressed-air car is analyzed in [48], which also considers the merits of compressed air versus chemical storage of potential energy. A system that recovers heat for cabin cooling for ejector and absorption cooling cycles is proposed in [49]. Energy and exergy analyses are conducted in order to study the role of various design parameters on the cooling capacity. The waste heat from the battery pack, as well as from exhaust gases in the ICE mode are the main inputs for the boiler and generator. To date, most of the studies on the pneumatic hybridization of ICEs deal with a two-stroke pure pneumatic mode. A few of the concept studies deal with a hybrid pneumatic–combustion four-stroke mode. Liquid nitrogen as a combustion-free and non-polluting vehicle fuel is investigated by Ordonez [50], who developed an open cycle engine. Overall, it is shown that a compressed air or liquid air (nitrogen) vehicle is worthy of consideration as part of the future sustainable vehicle solution. Liquid nitrogen is very similar to liquid air in behavior. One air propulsion experimental study of a 150 kg weight motorcycle with a rotating-vane air motor shows an observed efficiency of 40%; the range is observed as 2 km with a 10-liter compressed air tank [51]. A liquid nitrogen-powered engine and an air-compressed engine are also compared in [28]

where the overall efficiency of the liquid nitrogen-powered engine is in the range of 3.6% -14% and is reported to reach 26.9%. The overall efficiency of the compressed air-powered engine is 25%, 32.3% and 34.4% under pressures of 1 MPa, 3 MPa, and 6 MPa, respectively. The performance of the air motor is crucial for obtaining a reasonable overall system efficiency [52]. Moreover, the existing cryogenic liquid technology can be adapted and there is enough know-how that assures the safety of the solution. Liquid nitrogen as a combustion-free and non-polluting vehicle fuel is investigated in by Ordonez [50] who developed an open cycle engine. Overall, it is shown that compressed air or liquid air (nitrogen) vehicle is worthy of consideration as part of the future sustainable vehicle solution. Liquid nitrogen is very similar in behavior to liquid air. A cryogenic engine concept that uses solar heat to raise the enthalpy of the cryogenic nitrogen before expansion, showing promising efficiency, was also investigated in [50]. Hybrid engines, where braking energy is restored as compressed air and reused to power the vehicle, increase fuel efficiency by up to 64 % in town and cities and 12 % on motorways [53]. Various engine configurations and other vehicle systems based on compressed air are reported in the literature, including: a hydraulic coupled compressed gas regenerative braking system [54]); hybrid systems [37]; and supercapacitor-based systems [55]. The efficiency of a compressed air system in [56] is identified to have 10-20% efficiency; waste heat and leakage are the main drawbacks. Since 2006, the engineering research Center for Compact and Efficient Fluid Power at the University of Minnesota has been developing a hydraulic hybrid passenger vehicle with a hydro-mechanical transmission (HMT) drive train with regeneration and independent wheel torque control [57]. There are many studies regarding the control systems of the PV, one of the significant areas in need of more attention. As an example, the low-level control for a prototype hydro- mechanical transmission drive train with independent wheel torque control is reported in [45] while the speed and direction control of a motor is examined in [58]. Coupling of air motors with an ICE with heat recovery from exhaust gases is studied in [59] as a possible way to improve the system efficiency. It is known that the overall thermal efficiency of an ICE is around 20-30%. It is claimed that the optimization of the internal-combustion and recycling of the exhaust energy can increase the thermal efficiency to be around 18% [37].

A comparison between conventional ICEs powered by gasoline, EVs, compressed air vehicles and hybrid compressed air vehicles is made in [48], where it is concluded that the pure compressed air vehicle is least efficient while the hybrid compressed model shows remarkable performance. In fact, it is suggested that hybrid vehicles of the gasoline-compressed air kind are more economically and ecologically attractive than gasoline-electric battery vehicles. Through thermodynamic analysis, the study demonstrates an upper bound of overall efficiency of ~30% with a weight reduction of 60% with respect to EVs. In [28] it is suggested that liquid nitrogen or liquid air can be an improved alternative to a compressed air vehicle. The density of energy storage for these options is similar to that of a Ni-H electric battery as per volume basis. For a comparison per mass basis, the compressed air vehicle is 25% better than the EV, while liquid nitrogen shows a double storage density.

CHAPTER 3: CONCEPTUAL DEVELOPMENT OF PNEUMATIC CONFIGURATIONS 3.1 Introduction This section introduces four propulsion systems, namely a compressed air vehicle (CA); a compressed nitrogen vehicle (CN2); a liquid nitrogen vehicle (LN2); and compressed carbon dioxide (CCO2). These systems are included in the pure systems category:  Compressed air vehicle (CA)  Compressed nitrogen vehicle (CN2)  Liquid nitrogen vehicle (LN2)  Compressed carbon dioxide (CCO2) Six proposed system configurations are assessed: Compressed air + Internal Combustion +

Hydrogen vehicle (CA+ICE+H2); Compressed air + Internal combustion engine + Compressed natural gas (CA+ICE+CNG); Compressed air + Internal combustion engine + Liquid Propane gas vehicle (CA+ICE+LPG); Compressed air + Internal combustion engine (CA+ICE); Compressed Air + Internal Combustion Engine (CA+ICE); Compressed Air + Internal Combustion Engine (CA+ICE). All systems are considered as hybrid systems since they use at least two sources of energy. Six systems are included in the Hybrid Systems category:  Compressed air + Internal combustion + Hydrogen vehicle (CA+ICE+H2)  Internal combustion engine + Compressed natural gas (CA+ICE+CNG)  Compressed air + Internal combustion engine + Liquid propane gas (CA+ICE+LPG)  Compressed air + Internal combustion engine (CA+ICE)  Compressed air + Internal combustion engine (CA+ICE) with Heat recovery  Compressed air + Internal combustion engine (CA+ICE) with four-stage expansion In order to fill up the compressed air tank of hybrid systems, two ways are considered, the first of which is to pump the car’s tank from a compressed air station which has more than 350 bar pressure. The second method involves parking in the vicinity of a gas station. The ICE turns the air motor, which operates in reverse, as a compressor, and charges the tank using atmospheric air. Hybrid vehicles also appear to be a possible solution to cleaner transportation, especially for their ability to run mostly on compressed air in cities, thus lowering emissions, and running mostly on hydrocarbon fuel on highways as this increases driving range. As part

of the studied hybrid systems, various fuels were considered, including gasoline, LPG (liquid petroleum gas), CNG (compressed natural gas), and hydrogen, in various power generator configurations. Basically, the heat rejected by the combustion engine is used to heat the compressed air before expansion. The mechanical power developed by the compressed air doubles when heating is applied.

3.2 Compressed air

Figure 3.1 shows an illustration of a compressed air vehicle and Figure 3.2 shows schematic introducing the diagram of a compressed air vehicle with a four-stage expansion motor and inter-stage reheating. As is recognized, when air is expanded with a large expansion ratio, the temperature is dramatically reduced; any moisture in the air may cause freezing, which affects the air motor operation. In order to avoid this problem, this system requires heat addition before expansion.

Figure 3.1 Illustration of a compressed air (CA) vehicle.

Although, in order to meet heat demand, use of a solar collector or regenerative braking system is proposed, neither of these solutions are practical since they appear costly and complicated. As mentioned, a heat exchanger benefits the system by avoiding a freezing effect.

Moreover, increasing air temperature before entering the expanders will increase the system work potential and will directly improve system efficiency. Compressed air first enters the tank at a pressure of 350 bar. The compressed air next enters the regulator, then the first turbine with 60 bar pressure. The air temperature drops from 25℃ to -35℃.

Heat exchanger/Storage

5 7 9 10

4 6 8 Shaft Power Air Air Air Air Motor 1 Motor 2 Motor 3 Motor 4 1 3 2 Compressed Air Regulator

Figure 3.2 Schematic of a four-stage compressed air (CA) vehicle.

The cold air is heated after entering the heat exchanger. The temperature rises by 15℃. Each time it enters the next stage turbine, the air pressure decreases from 60 bar to 22 bar, then 8 bar. At 1 bar, it finally enters the atmosphere.

3.3 Compressed nitrogen vehicle

It has been mentioned in previous chapters that there are many studies related to compressed nitrogen fuelled cars due to environmental and economic reasons. As an energy carrier, compressed nitrogen can be accepted as an environmentally friendly fuel and its abundance can be a benefit in some aspects that will be explained in the next sections. Figure 3.3 shows illustration of a nitrogen vehicle and Figure 3.4 shows schematic introduces the diagram of a nitrogen vehicle with a four-stage expansion motor and inter-stage reheating. It should be noted that compressed nitrogen can be produced from an air separation plant powered by renewable energy. It is ready to use as a fuel with 300 bar, 25 o C for the four-stage expander featured in 31

this work. Detailed results and simulation results can be seen in the following chapters. Compressed nitrogen tank pressure is 350 bar at the beginning. It first enters the regulator, then enters the first turbine with 60 bar pressure. The nitrogen temperature drops from 25℃ to -35℃. The cold nitrogen is heated after entering the heat exchanger and the temperature rises by 15℃. Each time it enters the next stage turbine, the air pressure decreases from 60 bar to 22 bar, then 8 bar, and, finally, at 1 bar it enters the atmosphere. Nitrogen and compressed air are almost similar.

Figure 3.3 Illustration of a compressed nitrogen vehicle (CN2)

Heat exchanger/Storage

5 7 9 10

4 6 8 Shaft Power Air Air Air Air Motor 1 Motor 2 Motor 3 Motor 4 1 3 2

Compressed N2 Regulator

Figure 3.4 Schematic of a four-stage compressed nitrogen vehicle (CN2). 3.4 Liquid nitrogen vehicle

Liquid nitrogen is stored in a thermally isolated double shell tank at cryogenic temperature and low pressure (1-2 bar, -196oC). Figure 3.5 illustrates some of the main components of a liquid nitrogen propulsion unit and Figure 3.6 is schematic of a four-stage liquid nitrogen vehicle. The pump is used to increase the pressure of liquid form. The four heat exchangers are used for heat recovery while a four-stage turbine behaves as an expander.

Figure 3.5 Illustration of a liquid nitrogen vehicle (LN2).

Heat exchanger/Storage 13 Compressor 4 7 10 14

9 3 6 12

5 8 11

Shaft Power Air Air Air 2 Motor1 Motor2 Motor3 Pump 1 N2 Cryogenic N2

Figure 3.6 Schematic of a four-stage liquid nitrogen vehicle (LN2). Being in liquid form, cryogenic nitrogen is therefore denser than compressed nitrogen, over which it offers some benefits. Firstly, due to its liquid form, nitrogen can be pumped at high pressure with low work input. Secondly, being a low temperature liquid, ambient air can be used as a heat source to boil nitrogen and increase its enthalpy before expansion for enhanced work generation. Thirdly, the energy density of cryogenic nitrogen, both per unit of volume and mass, is higher that of any other studied gases.

3.5 Compressed carbon dioxide

Using compressed carbon dioxide as a propulsion fuel is a very new idea (as advanced in this project). This novel system might generate a significant positive effect on fuel economy and environmental impact since carbon dioxide can be harvested from many chemical operations, such as combustion, which releases significant amounts to the atmosphere every year. However, the first aim should be the implementation of CO2 as an energy storage medium derived from biomass or other carbon neutral sources. Figure 3.7 displays the block diagram of a compressed

CO2 vehicle and Figure 3.8 illustrates compressed carbon dioxide (CCO2). This system is similar to others in having four heat exchangers and a four-stage turbine. The only difference is in the type of propulsion fuel. It should be noted that simulation of this system can be seen in detail in the results and discussion section.

Heat exchanger/Storage

6 8 10 11

5 7 9 Shaft Power Air Air Air Air Motor1 Motor2 Motor3 Motor4 1 4 2 3 Pressurized CO2 Valve

Figure 3.7 Schematic of four-stage compressed carbon dioxide (CCO2).

Figure 3.8 Illustration of compressed carbon dioxide (CCO2).

3.6 Compressed Air, Internal Combustion and Hydrogen Vehicle This system consists of high-pressure liquid hydrogen and air. Figure 3.9 is illustration and Figure 3.10 is a schematic of combined compressed air and internal combustion with hydrogen fuel vehicle. Both are considered to be a propulsion fuel. Hydrogen can also be combusted with ambient air but, in this system, it is considered that burning hydrogen with compressed air can make a positive contribution to the ICE’s thermal efficiency. As an example, using less hydrogen burning with compressed air can produce more work output than burning the same amount of hydrogen with ambient air, which increases the IC’s thermal energy efficiency since the air is already compressed. Thus, an engine does not need to spend any work to compress this air. However, two separate tanks are needed for this operation. The philosophy is the same with supercharged cars where a recovery increases the exhaust gas pressure to re-cycle to the engine in order to produce more work output.

Figure 3.9 Illustration of compressed air + internal combustion + hydrogen (CA+ICE+H2).

2 3 7 Hydrogen Regulator Shaft 1 Power Exhaust Expander

5 6 8 9 Compressed Air Regulator ICT 4

Figure 3.10 Schematic of compressed air + internal combustion + hydrogen (CA+ICE+H2).

3.7 Compressed air, internal combustion engine and compressed natural gas

Figure 3.11 is Schematic of an internal combustion engine with the fuel of compressed natural gas that injects air from compressed air tank system, Figure 3.12 shows the block diagram of compressed air and natural gas with a combustor. System 3.10, System 3.12 and System 3.14 have the same approach with respect to having an ICE and compressed air, the only difference being the type of burning fuel. It should also be highlighted that the engine heat can be utilized through heat exchangers to supply more energy to the system. The system simulations and comparisons with other systems will be explained in further chapters.

Figure 3.11 Illustration of internal combustion engine, natural gas and air (CA+ICE+CNG).

2 3 7 CNG Regulator Shaft 1 Power Air Exhaust Motor

5 6 8 9 Compressed Air Regulator ICT 4

Figure 3.12 Schematic of internal combustion engine, natural gas and air (CA+ICE+CNG). 3.8 Compressed air, internal combustion engine and liquid propane gas

Figure 3.13 is a 3D picture of an internal combustion engine vehicle energy system with fuel of liquid propane gas that works with compressed air and Figure 3.14 illustrates the block diagram of the system, which mainly consists of compressed air and liquid propane with an ICE. The propane fuel reacts with air in the combustion chamber and is passed to the turbine that generates the power required to propel the vehicle. The turbine is connected to the motors that rotate and provide the required rotational speed of the wheels. This vehicle will also be compared with others and the results will be available in the next chapters. Furthermore, this system’s simulated components will be explained in the results and discussion section in result chapter.

Figure 3.13 Illustration of internal combustion engine, liquid propane gas and compressed air

2 3 7 LPG

Regulator Shaft 1 Power Air Exhaust Motor

5 6 8 9 Compressed Air Regulator ICT 4

Figure 3.14 Schematic of an internal combustion engine, liquid propane gas and compressed air (CA+ICE+LPG)

3.9 Internal combustion engine and compressed air system

As previously mentioned different fossil fuel combinations with compressed air were investigated and several assessments were conducted in order to determine the overall picture in terms of thermodynamic efficiency. Figure 3.15 is a 3D picture of an internal combustion engine vehicle energy system with fuel of gasoline that works with compressed air and Figure 3.16 illustrates the block diagram of the system. It is also clear that some heat recovery is obtained at the heat exchangers. This system includes the usage of gasoline as fuel in comparison with the previous system that included propane fuel in the combustion chamber. The system also includes a single-stage heat recovery process to utilize the available waste heat in the system.

2 7 Gasoline 1 Pump Shaft Power Exhaust Expander

5 6 8 9 Compressed Air Regulator ICT 4

Figure 3.16 Schematic of a compressed air + internal combustion engine (CA+ICE).

Figure 3.15 Illustration of a compressed air + internal combustion engine (CA+ICE).

3.10 Compressed air, internal combustion engine with heat recovery

Figure 3.17 is schematic of a compressed air, gasoline internal combustion engine with heat recovery that injects air from compressed air tank system. This kind of system is claimed that utilizing exhaust gas could increase 18% of the total system performance. [37] As can be observed from figure 3.17, the 3D diagram of the air expander is combined with an ICE. In this system, an ice engine is designed to provide work for compressing air, which will be mixed with the exhaust gas in the air motor to produce more work output. The main purpose of performing this simulation is to investigate this system in order to calculate how exhaust gas can affect the system performance with contributing waste heat to the system.

3.11 Internal combustion engine and compressed air four-stage expansion

A block diagram of a four-stage recovery internal combustion engine combined with compressed air is illustrated in Figure 3.18. The ICE engine supplies enough heat to preheat and reheat the expanding air by using heat exchangers between the expansion stages. Both the exhaust gas and the radiator fluid are used for this purpose. As far as the compressed air is available on the vehicle, the driving is in hybrid mode, consuming a small amount of gasoline.

When the air tank is emptied, the driving continues only with a four-stage recovery internal combustion engine. The novelty of the system is entailed in the multiple stages of waste heat recovery.

Figure 3.17 Illustration of compressed air + internal combustion engine (CA+ICE) with heat recovery.

Figure 3.18 Illustration of compressed air + internal combustion engine (CA+ICE) with four- stage expansion.

CHAPTER 4: EXPERIMENTAL APPARATUS AND PROCEDURE

4.1 Introduction This section introduces three propulsion systems, namely: a compressed air system with heating element prototype; a compressed air system with a PCM heat exchanger prototype; and a hybrid compressed air-electric system prototype. The three different prototypes built and tested are listed as follows:

 Compressed air system with a heating element (System 1)  Compressed air system with a PCM heat exchanger (System 2)  Hybrid compressed air-electric system (System 3)

Figure 4.1 Compressed air system with PCM heat exchanger prototype.

These prototypes of PV systems consist of three separate novel compressed air or hybrid systems, which have been built and tested. Figure 4.1 illustrates the compressed air system with heating element prototype while Figure 4.2 shows the compressed air system with a PCM heat exchanger prototype. Figure 4.3 reveals the hybrid compressed air-electric system prototype.

Figure 4.2 Compressed air system with heating element prototype.

Figure 4.3 Hybrid compressed air-electric system prototype.

4.2 Compressed air system with heating element prototype This prototype demonstrates the application of compressed air as a source of energy and as a non-polluting fuel in driving an automobile [69].

4.2.1 Description of prototype system 1 Figure 3.4 illustrates a compressed-air prototype powered by air engines, using compressed air that is stored in tanks. Instead of mixing fuel with air and burning it in the engine to drive air motors and a turbine with hot expanding gases, the prototype uses the expansion of compressed air to drive the air motors. The electricity requirement for heating air has to be considered while computing overall efficiency. Nevertheless, the compressed air vehicle will contribute to the long-term reduction of urban air pollution.

Figure 4.4 Schematic of compressed air system with heating element system

This prototype uses components such as an air motor, a turbine and valve, fiberglass heating tape, air tanks, a generator, and wheels to realize the concept and also execute different engineering concepts combined to work as a single system. During acceleration, the air in the air storage device may travel to the regulator device, a single-stage pressure regulator in the present prototype. The regulator device may reduce an airflow pressure output from the air storage device to optimal operating pressure wherein the regulator device may be configured to reduce the pressure from the exemplary 320 bar to an exemplary, without limitation, 7 bar. The adjustment valves may be configured to provide air adjustments to the air motors when the vehicle may be turning. Air motor exhaust from each of the air motors may be combined with the exhaust multidirectional mixer, where the exhaust multidirectional valve may be further configured to pass the combined air back to the turbine [60]. The air absorbs heat during travel from connection pipes through heating elements around the pipes. At Stages 5, 6, 7 and 8, air goes inside the air motors and, after expanding and turning the air motor shaft at point 8, air gathers into mixer B and goes into the turbine. Generated electricity uses heat elements to heat air through pipes during the process. In many embodiments, the pneumatic power system may be, for example, and without limitation, a compressed air power system, wherein the air storage device may be configured to store compressed air. In some exemplary alternative embodiments, the air storage device may include a multiplicity of operably coupled tanks, wherein each tank may be in a range of particular sizes, volumes, shapes, and structures. The prototype used two high pressured tape T metal tanks with a pressure of 4650 psi and a volume of 6.96 ft3.

4.2.2 Experimental procedures for prototype 1 The compressed air system with a heating element prototype, built in the ACE at Ontario Tech University, Oshawa, and, as shown in Figure 4.5, consists of air motors, a turbine and valve, fiberglass heating tape, air tanks, a generator, pipe connectors, a regulator and convertor, wheels and other parts. For testing the built prototype, the primary need was to provide an independent, full test capability for prototype operation testing in support of the automotive industry. It was subsequently tested three times on an ACE dynamometer to obtain prototype correct with comparable results.

Figure 4.5 Actual Prototype 1 System.

4.3 Compressed air system with PCM heat exchanger prototype This compressed-air prototype, with an air motor, regulator, turbine, valve, air tank, generator, wheels and auxiliary components as PCM and a regular heat exchanger, are used for recovering and inter-stage reheating of expanding air [70].

4.3.1 Description of prototype 2 system As shown in Figure 4.6, the air from the main storage tank travels to a pressure regulator that reduces the pressure to 807kP, which is the operating pressure for the four drive motors.

Figure 4.6 Compressed air system with PCM heat exchanger prototype.

The air motor inlet occurs in States 5, 6, 7 and 8, respectively. After expansion in the wheel’s motors, the air becomes colder in States 9, 10, 11 and 12, respectively. The expanded air from the air motors is collected in Stream 13. Therefore, this air passes through the heat exchanger with PCM storage option and reheated using the thermal storage onboard. Furthermore, the second stage of expansion occurs in the turbine that drives an electric

generator for onboard power requirements. When air is expanded with a large expansion ratio, the temperature is dramatically reduced, and battery and generator power might be applied to meet system heat demand. As mentioned in X.x.x, one of the benefits of a heat exchanger is that it avoids a freezing effect on the system. Increasing air temperature before entering the expanders will increase system work potential and will directly improve system efficiency. PTC (positive temperature coefficient) components during the test period are inside the PCM in order to store and heat up the PCM heat exchanger materials and provide the required energy to heat air through the heat exchanger. In colder days of the year, the external plug may need to be plugged into a prototype heat exchanger/storage. While the prototype is in a station, it can be plugged in for fast recharging of the battery and, at the same time, it can store heat in the PMC. In the present prototype, the pneumatic power system may include a multiplicity of air storage devices. A regulator device may reduce gas pressure from the gas storage device from an exemplary. The pneumatic power system may also include an exhaust multidirectional valve, wherein the exiting air (exhaust) from each of the pneumatic motors may be directed towards and collected in the exhaust multidirectional valve, which may be configured to direct the collected exhaust back toward the first heating unit to be reheated, whereby the reheated gas may be directed toward and through an exhaust motor, thus turning the exhaust motor. Moreover, the exhaust motor may be operably coupled to the first generator, wherein the turning of the exhaust motor may cause the first generator to produce and output an electrical charge. At the lowest pressure, air collected from a multiplicity of vehicle components may be expanded in a single air turbine. 4.3.2 Experimental procedures for prototype 2 The compressed air system with a PCM heat exchanger prototype, built as shown in Figure 3.7, consists of air motors, a turbine and valve, fiberglass heating tape, air tanks, a generator, pipe connectors, a regulator and convertor, wheels and heat exchangers. The prototype was table built and tested with three types of PCM in order to determine the results given in Chapter 6. A type of rope brake dynamometer is used to measure the power from rotating the shaft. This test system basically works on the principle of absorption of power. A digital torque tester connected to the shaft showed the amount of torque during the test.

Figure 4.7 Actual prototype 2 system

4.4 Hybrid compressed air-electric system prototype The pneumatic system is the primary system whereas the electric system acts as a backup, extending the driving range in the case where the compressed air onboard runs out [71].

4.4.1 Description of prototype 3 system As shown in Figure 4.8, the air from the main storage tank travels to a pressure regulator that reduces the pressure from to 807kP, which is the operating pressure for the two drive motors at the vehicle front. The air from the regulator travels to a three-way valve which lets in air from the main storage tank.

Figure 4.8 Hybrid compressed air-electric system prototype.

The exemplary power system of the prototype may include both an electric power system and a compressed air power system, wherein the electric power system and the compressed air power system may be interconnected. In the present prototype, the power system architecture may include an air tank, a regulator device, a PCM heat exchanger, an input multidirectional valve, two pneumatic motors, a turbine, a generator, a multiple battery system, 50

a charging system, a heating exchanger, two electric motors, and a multiplicity of wheels. In the present prototype, the air storage device be operably coupled to regulator device. This regulator device includes a pressure regulator such as, without limitation, a single stage pressure regulator. The regulator device is further operably coupled to the first heating unit, whereby the first heating unit includes a heat exchanger comprising PCMs, such as, and without limitation, liquid paraffin, paraffin wax(candle), polyethylene glycol (hot pack), and alkane mix(antifreeze). A heat transfer may occur when a material changes from solid to liquid, or liquid to solid. Thus, when the ambient temperature is low, these solid-liquid PCMs may perform similar to self-regulating thermal storages, wherein their temperature may rise as they absorb heat. In the present prototype, two electric motors, hence power, may be directly transmitted to the wheels as opposed to possibly having to propagate through a multiplicity of powertrain elements as with the prototype. Electricity be directly provided when a battery and convertor are switched on. When the air tank is depleted, a trigger button changes to drive the electricity mode. At least two systems, working in conjunction, may also provide multiple layers of redundancy for the operation. An operator may choose which power system to power the prototype and switch back and forth as desired. Furthermore, both systems may be used at any time as necessary. The air motor powers the prototype as front-wheel drive and the electric motors operate as rear-wheel drive. If required, the prototype can work as an all-wheel drive system [61]. 4.4.2 Experimental procedures for prototype 3

The hybrid compressed air-electric system prototype, built as shown in Figure 3.9, consists of all the components of the second prototype plus the addition of electric motors and a better battery storage system. The prototype was table built and tested with three different PCMs in a heat exchanger in order to identify the best efficiency. A rope brake dynamometer connected to a digital torque tester is used to determine the rear electric motors and front air motor torque. This test system basically works on the principle of absorption of power. A digital torque tester connected to the shaft showed the amount of torque t during the test.

Figure 4.9 Actual prototype 3 system

4.5 Experimental system elements, tools and parameters

This section describes the components, devices, and procedures for the three prototype systems. Table 4.1 includes technical data related to major system elements. The first prototype is tested on a dynamometer in order to obtain mostly mechanical as well as some thermodynamic results while the second and third prototypes undergo stationary testing on a table in order to obtain mostly thermodynamic as well as some dynamic results.

Table 4.1: Technical data related to system elements Air Motor 16AM The 16AM air motor series offers Horsepower: 6.73 kW variable operating speeds and power Net weight: 36.3 kg output that can be adjusted to meet the Series: 16AM precise needs of the prototype Maximum torque: 372 lb./in applications. It can be stalled or Maximum speed: 2,000 rpm overloaded for long periods without Torque at max 290 lb/in damaging the motor. In addition to being speed: a non-electrical device with cool Speed at max 300 rpm running, Gast air motors are ideal for use torque: in hazardous and extreme ambient Maximum 7.0 bar temperature locations. pressure: Manufacturer: Gast Air Motor 8AM The 8AM air motor differs in many ways Horsepower: 4.0 kW from other power sources. It is easy to Net weight: 14.54 kg change the power and speed of the air Series: 8AM motor by throttling the air inlet. Maximum torque: 185 lb/in Therefore, the best rule of thumb for Maximum speed: 2,500 rpm selecting an air motor is to choose one Torque at max 132 lb/in that will provide the power and torque speed: needed using only two-thirds of the line Speed at max 300 rpm pressure available. The full airline torque: pressure will then be available for Maximum 7.0 bar overloads and starting. pressure: Electric motors The electric motor is a totally enclosed Type AC/DC and fan cooling, three-phase squirrel Output 7.5 kW cage electric motor that is designed Speed 2910 rpm according to IEC standards. This Amps 14.3 A electrical motor is applied in mechanical EFF 89.5% and electro-mechanical industries. P.F. (Cosφ) 0.89 Noise 79 dB Fiberglass Wrap on, insulate and plugin. Product Number HTC-060 heating tape Engineered for use on metal pipes, Temperature 482°C

fiberglass pipe wrap is required to Power 125 W complete the installation. Designed for Power density 1.8 W/in2 use on tubes, vessels, or any application Heater length 6 ft where space is limited, this tape can be Supply voltage 120 V wrapped around objects. Width/Diameter Ø 3/16 in Lead wire length 24 in Insulation Fiberglass material PT Cheating PTC heating elements are self-limiting; Operating voltage 12V AC/DC elements i.e., they can be used in an unlimited Power 400W application range. They are mostly used Heating element PTC resistor for heating solid bodies, containers, Heater body Aluminum, industrial fluids and appliances, and Anodized medical equipment, as well as in Mounting Screw cosmetic sectors and a variety of fixing household appliances. Fitting position Variable Operating/Storage -45 °C to temperature +70 °C Air Tanks Gas storage tubes, which are for larger Cylinder type T- HPS volume high-pressure gas storage units, Pressure 45870 psi known as tubes, are available. They Volume 1.73 ft3 generally have a larger diameter and 48.99 L length than high-pressure cylinders, and Nominal 9.25 in usually have a tapped neck at both ends. dimensions diameter 55.00 in height Average tare 143 lb weight 64.86 kg Mastercraft tank The air tank can be filled from any air Cylinder type Mastercraft service station or air compressor. The Working pressure 105-135 psi tank, which produces a maximum pressure of 135 psi, comes standard with Water capacity 48.99 kg an air-line shutoff and manual pressure Nominal 9.25 in relief valve. It also features an air chuck, dimensions diameter pressure gauge, and standard tire air 55.00 in chuck gauge and three feet of industrial- height grade hose. Weight 64.86 kg

Generator A generator of electric power is a major Voltage 12 V component of the vehicle's charging Amps 250 system. When the system’s turbine is Weight 7.18 kg

running, the alternator charges the Product 22.9 x 20.3 battery and supplies additional electric dimensions x 20.3 cm power for the vehicle’s heating system. Model number 8292N253A

Regulator Pressure Regulator 44-1300 Series Maximum inlet 414 bar Valve is a high flow pressure reducing pressure regulator that offers a venting and Outlet Ranges 0-103 bar balanced valve design. The 44-1300 Body Material Brass Series provides CV equal to 0.8 and 2.0. Main Valve CTFE It is ideal for high-pressure tube gas Vent Valve CTFE: 1500 reduction. psig outlets Port Size 3/4SAE, Temperature 26-104°C Flow Capacity CV = 2.0 Weight 2.8 kg Fiberglass The selected crystalline solar panel is Power 100W heating tape ideal for use with remote and back-up Volt 12V power use, as well as 12V battery Solar technology Crystalline charging. Panel features are high Solar efficiency crystalline solar cells for long- Width 3.5 cm lasting use. It can be used in tandem with Depth 101 cm a charge controller to protect the 12V Product model 51880 battery. A charge-carrier collection in a Output amperage 5.8 A crystalline silicon solar cell is achieved Weight 7.9 kg by minority-carrier diffusion within the p‐doped and n‐doped layers. Power Inverter The Mobile Power Inverter converts 12 High voltage 15.5V V DC power into 120V household AC Max efficiency 87 Percent power. It is connected to the 12V battery Output frequency 60 Hz in the vehicle, a standalone 12V battery, Weight 4.80 kg or a bank of batteries to run AC powered Output voltage 115.0V AC devices in cars. Sine wave output form is Overload Yes compatible with most AC uses. AC protection outlets provide a total combined Input voltage: 11.0 V DC continuous running capacity of 3000W Output capacity: 3000W and 6000W surge capacity. Full load current: 300A AC capacity: 6000W Low voltage: 10.5 V DC Polyethylene Polyethylene glycol is a superabsorbent Molecular weight 1020 Glycol polymer with the ability to absorb 100 to Melting point 60 ◦C 1000 times its mass in water. This Specific gravity 1.1 material is an anionic polyelectrolyte Specific heat 2.26 kJ/kg 55

with negatively charged carboxylic Latent heat 154.9 kJ/kg groups in the main chain. Sodium Flame 265 ◦C neutralized polyacrylic acids are the temperature most common form used in industry. PH value 5.5 Weight 7.9 kg

Alkane mix Water and an alkane mixture have also Specific heat 2.0 kJ/kg K been used as PCM in this prototype. capacity Typically, solids have lower specific Solid density 0.88 kg/L heats than liquids. When the PCM Liquid density 0.76 kg/L warms to the temperature at which it Thermal 0.2 W/m K changes phase (melting point), the PCM conductivity will absorb large amounts of heat Total mass 8.28 kg without becoming hotter. Volume 13 % expansion PCM heat A PCM heat exchanger is used to Inlet temperature -35 ◦C exchanger describe the experimental investigation Outlet +15 ◦C conducted on the air-PCM heat temperature exchanger in order to measure its Mass flow 60 kg/h thermal performances. The test bench Pressure 22 Bar used in this thesis is based on the Operating 21.5 Bar experimental apparatus using three pressure different materials as PCM materials. Power 3981 W

Heat exchanger This copper pipe heat exchanger is a Inlet temperature -25 ◦C system designed to transfer heat between Exit temperature +10 ◦C the outside temperature with the inside Mass flow 56 kg/h of the pipes’ cold air. A wrapped heat Pressure 8 Bar element gives heat to flowed air. Operating 7.8 bar pressure Power in 1882 W

Table 4.2 presents a list of the measuring instruments used in building and testing all three prototypes. Technical data related to the system devices and equipment is also included. The measurement process provides the number of cases studied and the units of measurement referenced. The official test method that defines an instrument and its use are the means by which these numerical relationships are obtained. Every measuring instrument has varying degrees of instrument error and measurement uncertainty.

Table 4.2: Technical data of system devices and equipment ACE chassis The ACE chassis dynamometer is Roll width 812 mm dynamometer designed to provide a multitude of Roll diameter 1219 mm industries with world-class and Roll surface Finish (0.8µ) independent testing capabilities to Clear space between 1,067 mm validate prototype products under rolls different conditions. Climatic 1,600 to 5,842 Wheelbase range simulation systems include solar mm capabilities, rain, freezing rain, Total inertial light snow, and blizzards - all with 907 to 9,072 kg simulation wind speeds capable of 300 km/h at Maximum axle load 5,000 kg temperatures ranging from -40˚C Maximum vehicle 9,072 kg to +60˚C. The climatic wind tunnel weight at the ACE is also a full-scale Maximum speed 250 km/h chassis dynamometer to enable Nominal maximum 187 kW per roll product tests at yaw. In addition to power the vehicle performance Base speed 92 km/h information, the dynamometer Continuous tractive 7,301 N per system provides during a test, force roll specific engine performance characteristics can be monitored Tractive force (0-92 using instrumentation and 150 % for 60/s diagnostic equipment connected to km/h) the test vehicle. Digital clamp A digital-clamp meter measures AC current 100mA meter the AC current via the clamp, 1A AC/DC voltage, resistance and Insulation test 10kΩ continuity via test-leads, and the 1mΩ temperature via a thermocouple AC voltage 1V probe. DC voltage 1V Resistance 0.1Ω 10Ω

Digital A digital multimeter measures Functions 7-Function multimeter AC/DC voltage, AC/DC current, Ranges 19 ranges and resistance. It can also measure DC voltage 200V temperature, capacitance, AC voltage 300V frequency, duty-cycle, test diodes, DC current 10A and continuity. The manual range Resistance 2000kΩ dial makes it easy to select a range Battery 12V to measure current, voltage, Test type Diode and resistance and other parameters. A Continuity data hold feature saves

measurements for later viewing. 57

Multi-port data Included in the features of the 850 Input impedance 1 MΩ acquisition flexible interface are four digital Input protection ±250V interface inputs, four analog ports, a 15 W continuous function generator, and dual high- Speed sampling 2 channels up speed function generators. The four to 10 MHz digital inputs allow direct use of Frequency range 0.001 Hz to photogates and other digital 100 kHz sensors (such as Time-of-Flight), Amplitude range ±15 V with no adapter needed. Voltage Max out current 1 A at 15 V sensors are plugged into them to Current limit 1.5 A, 0.55 A measure voltages to ±20 V at Output current 61 μA at 10V sample rates of up to 10 MHz on 1 or 2 channels or 1 MHz on four Connection USB 2.0 (4890 channels. Mbps) External trigger 3.3 V, 510 Ω PT Cheating Getting accurate temperature Range -28°C - 482°C elements readings on engines, prototype Accuracy +/- 2% components. The LCD display is Resolution 0.1°C color-coded for faster temperature Response <500ms References. Set a target Distance 11:1 temperature and quickly see the Diode laser <1mW target temperature range. This Wavelength 630 - 670nm thermometer's awesome 11-to-1 Operating temp. 0°C - 50°C distance to spot ratio makes it easy Storage temp. -20°C - 60°C to take readings from a distance. This compact thermometer measures and displays temperatures from -2 to +482 degrees Celsius. Temperature This rugged sensor, which can Range –20 to 330°C Sensor measure temperatures in the range Maximum 380°C of –200°C to 1400°C, connects to a Resolution 0.10°C Vernier interface in order to collect data on the computer. The sensor Accuracy ±0.5°C establishes a ±0.5°C accuracy, as Voltage range 0.2 - 4.8 V well as excellent stability and Response time 30 s repeatability. Body length 17.0 cm

Probe length 24.5 cm Digital torque A digital torque adapter converts a Model YC-AUS2 tester standard 1/2" inch drive ratchet Capacity torque 1-135 Nm into an accurate digital torque range wrench. It can be set to the desired Square drive 9.5 mm torque value. Dimensions 45x24x75 mm

Weight 0.198 Drive 0.5 in

Digital Laser This tachometer is an instrument to Display 5 digits LCD Tachometer measure the rotational speed Testing range 2.5 - 99,999 (RPM) with a wide measuring RPM range and high resolution. It offers Resolution 0.1-1 rpm high accuracy measurement, quick Accuracy 0.05 % measuring time and a long Sampling time 0.8 s detecting distance up to 500 mm Detecting distance 50 - 500 mm (20 inches) with a laser. Time base Quartz crystal Operating temp. 0 - 50 ℃

Table 4.3: Measurement device accuracy and range

Variable Device Range Device Obtained Accuracy Accuracy

Potential Mastercraft Multimeter/ clamp meter 200mV-200V ± 0.003 V ±1mV Current Mastercraft Multimeter/ clamp meter 2000µA-10A ± 0.007 A ±5pA Resistance Mastercraft Multimeter/ clamp meter 200Ω-2000kΩ 200Ω ±10Ω Weight High Precision Lab Digital Scale 0.001g-10kg 0.01g ±0.01mg Temperature Vernier Temperature Sensor –20°C to 330°C 0.5 °C ±0.1°C Dimensions Mastercraft Digital Caliper 0.01-152mm 0.001mm ±0.001mm Pressure Fluke Pneumatic Pressure Gauge 0.01-350 bar 0.01 bar ±0.1bar Rotational AGPtek Digital Laser Photo 2.5-99,999 RPM 1 RPM ±0.1rpm Speed Tachometer Torque Generic YC-AUS2 Measure Ratchet 1-135 Nm 0.01 Nm ±1Nm Measuring Digital Torque Tools

4.6 Experimental error and measurement uncertainties The experimental measurements are subject to the accuracy of measurement devices, as well as bias and precision errors. These effects are quantified in experimental uncertainty. The value of the bias error represents the interval within which the true value lies. Precision errors represent

limitations of the repeatability of a measurement device and are statistically estimated. The measurement range and instrumental accuracies of the devices used in the experiments are given in Table 4.3. These are applied to the experimental measurements to determine the absolute uncertainty of the results given in Chapter 6. The propagation of experimental error in calculations is outlined according to the find error and measurement uncertainties method.

CHAPTER 5: ANALYSIS AND MODELING 5.1 Introduction The performances of the systems are evaluated by determining the energy and exergy efficiencies for all of the introduced integrated systems. From a thermodynamics perspective, isothermal compression requires the minimum mechanical energy input. In this chapter, basic equations of energy and exergy are introduced, and an analysis of the main powering options is described. In addition, equations of the dynamic analysis and the exergoeconomic analysis are provided. The following general assumptions apply for the baseline operating case:

 The reference To and Po are 298 K (25°C) and 100 kPa, respectively.  The processes occur at steady state.  The potential and kinetic energies are negligible.  The chemical reactions proceed to completion.  The gas and gas mixtures are ideal.  The compressor and pumps are adiabatic.  The pressure losses in all heat exchangers and pipelines are negligible.

5.2 Thermodynamic analysis A thermodynamic analysis of the suggested systems is based on energetic and exergetic approaches. Exergoeconomic concepts are used to economically analyze the developed systems. Thermodynamic analysis of the main components that are utilized in the proposed integrated system are also incorporated. The system performances are evaluated by determining the energy and exergy efficiencies for all of the introduced integrated systems. Basic equations of energy and exergy are also introduced in this chapter. An analysis of the main powering options is described. In addition, equations of the dynamic analysis and the exergoeconomic analysis are provided. Moreover, a section of the optimization study that is used in this thesis is included. [67] From the first law of thermodynamics, the conservation of mass and energy define the mass balance equation (MBE) and energy balance equation (EBE) by the general conservation of mass that can be expressed as follows: dm ∑ ṁ − ∑ ṁ = (5.1) in out dt

Here, 푚̇ denotes mass flow rate, and the terms “in” and “out” refer to the inlet and outlet of the control volume. The conservation of energy equation can be obtained from the first law of thermodynamics as follows:

E2 − E1 = δQ − δW (5.2) Here, E, Q, and W are the energy of the system, the heat, and work that the system exchanges with the environment. The general energy balance equation can be presented as follows:

u2 u2 Q̇ cv + ∑ ṁ in (h + + gz) = Ẇ cv + ∑ ṁ out (h + + gz) (5.3) 2 in 2 out where z is the elevation, V is the velocity and h is the specific enthalpy. The entropy generation can be determined using the following equation:

Q̇ ∑ ṁ s + ∑ cv + Ṡ = ∑ ṁ s (5.4) in in T gen out out where 푆푔푒푛̇ refers to the entropy generation and s is the thermodynamic property entropy. Exergy is the maximum useful work that can be obtained from a process. Exergy analysis is usually applied to detect the reasons for thermodynamic irreversibilities, known as exergy destruction, which enables a further improvement in the thermodynamic process. The exergy balance equation describing any system is presented as follows:

∑ Ė xQ + ∑in Ė xflow = ∑ Ė xw + ∑out Ė xflow + Eẋ d (5.5) where 퐸̇ 푥푄 represents the exergy transfer rate. Ė xflow represents the exergy flow that transfers in or out of the system. Ė xw refers to shaft work applied to or performed by the system. Finally,

Eẋ d is the exergy destruction. The thermal exergy flow can be described as follows:

T0 Ė xQ = (1 − ) Q̇ (5.6) Ti where (1 − 푇0⁄푇𝑖) where 푇0and 푇𝑖 are ambient and system temperatures, respectively. Exergy associated with work can be calculated as follows: dV Ė x = Ẇ + P cv (5.7) w cv 0 dt where 푃0 is the pressure of the dead state. Exergy associated with a steady stream can be determined as follows:

∑in Ė xflow − ∑out Ė xflow = ∑in ṁ iexi − ∑out ṁ iexi. (5.8) There are four main components of the flow exergy: physical, chemical, potential and kinetic exergy: 62

ph ch ke pe exflow = ex + ex + ex + ex . (5.9) The physical exergy components are stated as follows: ph ex = (h − h0) − T0(s − s0). (5.10) 5.3 Compressed air system with a heating element The balance equations for mass, energy, entropy and exergy are written for the components in a compressed air system with a heating element as follows: 5.3.1 Air motors The mass balance for the air motors can be written as follows: ṁ 5 = ṁ 9. (5.11) The energy balance for the air motors can be written as follows: ṁ 5h5 = ṁ 9h9 + Ẇ 퐴푀 . (5.12) The entropy balance for the air motors can be written as follows: ṁ 5s5 + Ṡ genAM = ṁ 9s9. (5.13) The exergy balance for the air motors can be written as follows: ṁ 5ex5 = ṁ 9ex9 + Ẇ AM + Eẋ dAM . (5.14) 5.3.2 Turbine The mass balance for the turbine can be written as follows: ṁ 13 = ṁ 14. (5.15) The energy balance for the turbine can be written as follows: ṁ 13h13 = ṁ 14h14 + Ẇ T. (5.16) The entropy balance for the turbine can be written as follows: ṁ 13s13 + Ṡ genT = ṁ 14s14. (5.17) The exergy balance for the turbine can be written as follows: ṁ 13ex13 = ṁ 14ex14 + Ẇ T + Eẋ dT. (5.18) 5.3.3 Mixer A and B For Mixer A, the mass balance equation can be written as: ṁ 4 = ṁ 5 + ṁ 6 + ṁ 7 + ṁ 8. (5.19) The energy balance equation for Mixer A can be written as: ṁ 4h4 = ṁ 5h5 + ṁ 6h6 + ṁ 7h7 + ṁ 8h8. (5.20)

The entropy balance equation for Mixer A can be written as: ṁ 4s4 + Ṡ genMA = ṁ 5s5 + ṁ 6s6 + ṁ 7s7 + ṁ 8s8. (5.21) The exergy balance equation for Mixer A can be written as: ṁ 4ex4 = ṁ 5ex5 + ṁ 6ex6 + ṁ 7ex7 + ṁ 8ex8 + Eẋ dMA. (5.22) For Mixer B, the mass balance equation can be written as: ṁ 13 = ṁ 9 + ṁ 10 + ṁ 11 + ṁ 12. (5.23) The energy balance equation for Mixer B can be written as: ṁ 13h13 = ṁ 9h9 + ṁ 10h10 + ṁ 11h11 + ṁ 12h12. (5.24) The entropy balance equation for Mixer B can be written as: ṁ 13s13 = ṁ 9s9 + ṁ 10s10 + ṁ 11s11 + ṁ 12s12 + Ṡ gen,MB. (5.25) The exergy balance equation for Mixer B can be written as: ṁ 13ex13 + Eẋ dMB = ṁ 9ex9 + ṁ 10ex10 + ṁ 11ex11 + ṁ 12ex12. (5.26) 5.3.4 Valve For the valve, the mass balance equation can be written as: ṁ 1 = ṁ 2. (5.27) The energy balance equation for the valve can be written as: ṁ 1h1 = ṁ 2h2. (5.28) The entropy balance equation for the valve can be written as: ṁ 1s1 = ṁ 2s2 + Ṡ genV. (5.29) The exergy balance equation for the valve can be written as: ṁ 1ex1 + Eẋ dV = ṁ 2ex2. (5.30) 5.3.5 Regulator For the regulator, the mass balance equation can be written as: ṁ 4 = ṁ 3. (5.31) The energy balance equation for the regulator can be written as: ṁ 4h4 = ṁ 3h3. (5.32) The entropy balance equation for the regulator can be written as: ṁ 4s4 + Ṡ genReg = ṁ 3s3. (5.33) The exergy balance equation for the regulator can be written as:

ṁ 4ex4 = ṁ 3ex3 + Eẋ dReg. (5.34) 5.3.6 Energy and exergy efficiencies of a compressed air system with a heating element For the systems considered here, the energy efficiency can be defined as the ratio of useful energy output to the total energy input. The exergy efficiency is defined here as the ratio of useful exergy output to the total exergy input. In this, the energy and exergy efficiencies for the air motors, turbine, mixer, valve, regulator and overall system are defined and evaluated.

푊̇ 퐴푀 Ẇ AM Air motors: ηenAM= and ηexAM= (5.35) 푚̇ 5ℎ5 ṁ 5ex5 Ẇ TA Ẇ 퐴푀 Turbine: ηenTA= and ηex,AM= (5.36) ṁ 13h13 ṁ 13ex13 The energy and exergy efficiency of the overall system (Figure 3.1) can be written as follows:

푊̇ 퐴푀1 +푊̇ 퐴푀2 +Ẇ 퐴푀3 +Ẇ 퐴푀4 +Ẇ T ηen,ov1= (5.37) ṁ 1h1+ṁ 2h2+Ẇ in,battery+Q̇ in,Electric

푊̇ 퐴푀1 +푊̇ 퐴푀2 +Ẇ 퐴푀3 +Ẇ 퐴푀4 +Ẇ T ηex,ov1= T (5.38) ṁ ex +ṁ ex +Ẇ +Q̇ (1− 0) 1 1 2 2 in,battery in,Electric T 5.4 Compressed air system with PCM heat exchanger analysis The balance equations for mass, energy, entropy and exergy are written for the components in the analysis of the system with a PCM heat exchanger as follows: 5.4.1 Heat storage unit (in PCM) The mass balance equation for the heating storage can be written as: ṁ 3 = ṁ 4. (5.39) The energy balance equation for the heating storage can be written as: Charging: uic ufc Qlosscharging ṁ 3h3 + Ẇ in battery + mPCM = mPCM2 + + ṁ 4h4 (5.40) Δt푐 Δt푐 Δt푐 Storing: uis ufd Qlossstorage mPCM = mPCM2 + (5.41) Δt푑 Δt푑 Δt푑 Discharging: uid ufd Qlossdischarging ṁ 3h3 + mPCM2 = mPCM + + ṁ 4h4. (5.42) Δt푑 Δt푑 Δt푑 The entropy balance equation for the heating storage can be written as: Charging:

Sic Sfc Qlosscharging ṁ 3s3 + mPCM + Ṡ gencharging = mPCM + + ṁ 4s4 (5.43) Δt푐 Δt푐 Δt푐푇0 Storing: Sis Sfs Qlossstorage mPCM = mPCM + (5.44) Δt푠 Δt푠 Δt푐푇0 Discharging: Sid Sfd Qlossdischarging ṁ 3s3 + mPCM = mPCM + + ṁ 4s4. (5.45) Δt푑 Δt푑 Δt푑푇0 The exergy balance equation for the heating storage can be written as:

Charging: (5.46)

exic exfc Qlosscharging T0 Exdescharging ṁ 3ex3 + Ẇ in battery + mPCM = mPCM + (1 − ) + ṁ 4ex4 Δt푐 Δt푐 Δt푐 TS Δt푐2 Storing

exis exfs Qlossstorage T0 Exdescharging mPCM = mPCM + (1 − ) + (5.47) Δt푠 Δt푠 Δt푠 TS Δt푠 Discharging:

exid exfd Qlossdischarging T0 ṁ 3ex3 + mPCM = mPCM + (1 − ) + ṁ 4ex4. (5.48) Δt푑 Δt푑 Δt푑 TS 5.4.2 Air motor The mass balance for the air motors A can be written as follows: ṁ 5 = ṁ 9. (5.49) The energy balance for the air motors A can be written as follows: ṁ 5h5 = ṁ 9h9 + Ẇ 퐴푀 . (5.50) The entropy balance for the air motors A can be written as follows: ṁ 5s5 + Ṡ gen,AM = ṁ 9s9. (5.51) The exergy balance for the air motors A can be written as follows: ṁ 5ex5 = ṁ 9ex9 + Ẇ AM + Eẋ d,AM . (5.52) 5.4.3 Turbine The mass balance for turbine A can be written as follows: ṁ 14 = ṁ 15. (5.53) The energy balance for turbine A can be written as follows: ṁ 14h14 = ṁ 15h15 + Ẇ T. (5.54) The entropy balance for turbine A can be written as follows: ṁ 14s14 + Ṡ genT = ṁ 15s15. (5.55)

The exergy balance for turbine A can be written as follows: ṁ 14ex14 = ṁ 15ex15 + Ẇ T + Eẋ dT. (5.56) 5.4.4 Mixer A and B For Mixer A, the mass balance equation can be written as: ṁ 4 = ṁ 5 + ṁ 6 + ṁ 7 + ṁ 8. (5.57) The energy balance equation for Mixer A can be written as: ṁ 4h4 = ṁ 5h5 + ṁ 6h6 + ṁ 7h7 + ṁ 8h8. (5.58) The entropy balance equation for Mixer A can be written as: ṁ 4s4 + Ṡ gen,MA = ṁ 5s5 + ṁ 6s6 + ṁ 7s7 + ṁ 8s8. (5.59) The exergy balance equation for Mixer A can be written as: ṁ 4ex4 = ṁ 5ex5 + ṁ 6ex6 + ṁ 7ex7 + ṁ 8ex8 + Eẋ dMA. (5.60) For Mixer B, the mass balance equation can be written as: ṁ 13 = ṁ 9 + ṁ 10 + ṁ 11 + ṁ 12. (5.61) The energy balance equation for Mixer B can be written as: ṁ 13h13 = ṁ 9h9 + ṁ 10h10 + ṁ 11h11 + ṁ 12h12. (5.62) The entropy balance equation for Mixer B can be written as: ṁ 13s13 = ṁ 9s9 + ṁ 10s10 + ṁ 11s11 + ṁ 12s12 + Ṡ gen,MB. (5.63) The exergy balance equation for Mixer B can be written as: ṁ 13ex13 + Eẋ dMB = ṁ 9ex9 + ṁ 10ex10 + ṁ 11ex11 + ṁ 12ex12. (5.64) 5.4.5 Valve For the valve, the mass balance equation can be written as: ṁ 1 = ṁ 2. (5.65) The energy balance equation for the valve can be written as: ṁ 1h1 = ṁ 2h2. (5.66) The entropy balance equation for the valve can be written as: ṁ 1s1 = ṁ 2s2 + Ṡ genV. (5.67) The exergy balance equation for the valve can be written as: ṁ 1ex1 + Eẋ dV = ṁ 2ex2. (5.68)

5.4.6 Regulator For the regulator, the mass balance equation can be written as: ṁ 2 = ṁ 3. (5.69) The energy balance equation for the regulator can be written as: ṁ 2h2 = ṁ 3h3. (5.70) The entropy balance equation for the regulator can be written as: ṁ 2s2 + Ṡ genReg = ṁ 3s3. (5.71) The exergy balance equation for the regulator can be written as: ṁ 2ex2 = ṁ 3ex3 + Eẋ dReg. (5.72) 5.4.7 Heat exchanger The mass balance equation for heat exchanger 1 can be written as: ṁ 13 = ṁ 14. (5.73) The energy balance equation for heat exchanger 1 can be written as: ṁ 13h13 + Q̇ in HX1 = ṁ 14h14+Q̇ loss HX. (5.74) The entropy balance equation for heat exchanger 1 can be written as:

Q̇ in HX Q̇ loss HX ṁ 13s13 + + Ṡ genHX = ṁ 14s14 + . (5.75) T0 T0 The exergy balance equation for heat exchanger 1 can be written as:

T ṁ ex + (Q̇ − Q̇ ) (1 − 0) = ṁ ex + Eẋ . (5.76) 13 13 in HX loss HX T 14 14 dHX 5.4.8 Energy and exergy efficiencies of system 2 The energy efficiency can be defined for the systems considered here as the ratio of useful energy output to the total energy input. The exergy efficiency is defined here as the ratio of useful exergy output to the total exergy input. In this, the energy and exergy efficiencies for the air motors, turbine, mixer, valve, regulator and overall system are defined and evaluated.

푊̇ 퐴푀 Ẇ AM Air motors: ηenAM= and ηexAM= (5.77) 푚̇ 8ℎ8 ṁ 8ex8 Ẇ T Ẇ 퐴푀 Turbine: ηenTA= and ηexAM= (5.78) ṁ 14h14 ṁ 14ex14 ṁ 4h4 ṁ 4ex4 PCM heat exchanger: ηenPHX= and ηexPHX= T0 (5.79) ṁ 3h3+Q̇ in PHX ṁ ex +Q̇ (1− ) 3 3 in PHX T ṁ 14h14 ṁ 14ex14 Heat exchanger: ηen,PHX= and ηex,PHX= T0 (5.80) ṁ 13h13+Q̇ in HX ṁ ex +Q̇ (1− ) 13 13 in HX T The energy and exergy efficiency of the overall system (Figure. 3.1) can be written as follows: 68

푊̇ 퐴푀1 +푊̇ 퐴푀2 +Ẇ 퐴푀3 +Ẇ T+Ẇ 퐴푀4 ηenOV= (5.81) ṁ 2h2+Ẇ in battery+Q̇ in HX+Q̇ in PHX

푊̇ 퐴푀1 +푊̇ 퐴푀2 +Ẇ 퐴푀3 +Ẇ T+Ẇ 퐴푀4 ηexov1= T . (5.82) ṁ ex +Ẇ +(Q̇ +Q̇ )(1− 0) 2 2 in battery in,HX in PHX T 5.5 Hybrid compressed air-electric system analysis The balance equations for mass, energy, entropy and exergy are written for the components in System 2 as follows: 5.5.1 Heat storage (PCM) unit The mass balance equations for the heating storage can be written as: ṁ 6 = ṁ 7. (5.83) The energy balance equation for the heating storage can be written as:

Charging uic ufc Qlosscharging ṁ 3h3 + Ẇ in battery + mPCM = mPCM + + ṁ 4h4 (5.84) Δt푐 Δt푐 Δt푐 Storing uid ufd Qlossstorage mPCM = mPCM + (5.85) Δt푑 Δt푑 Δt푑 Discharging uid ufd Qlossdischarging ṁ 3h3 + mPCM = mPCM + + ṁ 4h4. (5.86) Δt푑 Δt푑 Δt푑 The entropy balance equation for the heating storage can be written as: Charging

Sic Sfc Qlosscharging ṁ 3s3 + mPCM3 + Ṡ gencharging = mPCM + + ṁ 4s4 (5.87) Δt푐 Δt푐 Δt푐푇0 Storing Sis Sfs Qlossstorage mPCM = mPCM + (5.88) Δt푠 Δt푠 Δt푐푇0 Discharging Sid Sfd Qlossdischarging ṁ 3s3 + mPCM = mPCM + + ṁ 4s4. (5.89) Δt푑 Δt푑 Δt푑푇0 The exergy balance equation for the heating storage can be written as Charging exic exfc Qlosscharging T0 Exdescharging ṁ 3ex3 + Ẇ in battery + mPCM = mPCM + (1 − ) + + Δt푐 Δt푐 Δt푐 TS Δt푐 +ṁ 4ex4 (5.90) Storing exis exfs Qlossstorage T0 Exdescharging mPCM = mPCM + (1 − ) + (5.91) Δt푠 Δt푠 Δt푠 TS Δt푠

Discharging exi2d exf2d Qlossdischarging2 T0 ṁ 6ex6 + mPCM2 = mPCM2 + (1 − ) + ṁ 18ex18. (5.92) Δt푑2 Δt푑2 Δt푑2 TS 5.5.2 Air motor The mass balance for the air motors A can be written as follows: ṁ 5 = ṁ 7. (5.93) The energy balance for the air motors A can be written as follows: ṁ 5h5 = ṁ 7h7 + Ẇ 퐴푀. (5.94) The entropy balance for the air motors A can be written as follows: ṁ 5s5 + Ṡ gen,AM = ṁ 7s7. (5.95) The exergy balance for the air motors A can be written as follows: ṁ 5ex5 = ṁ 7ex7 + Ẇ AM + Eẋ d,AM. (5.96) 5.5.3 Turbine The mass balance for the turbine A can be written as follows: ṁ 10 = ṁ 11 (5.97) The energy balance for the turbine A can be written as follows: ṁ 10h10 = ṁ 11h11 + Ẇ T (5.98) The entropy balance for the turbine A can be written as follows: ṁ 10s10 + Ṡ gen,T = ṁ 11s11 (5.99) The exergy balance for the turbine A can be written as follows: ṁ 10ex10 = ṁ 11ex11 + Ẇ T + Eẋ d,T (5.100) 5.5.4 Mixer A and B For Mixer A, we can write the following mass balance equation: ṁ 4 = ṁ 5 + ṁ 6 (5.101) The energy balance equation for Mixer A can be written as: ṁ 4h4 = ṁ 5h5 + ṁ 6h6 (5.102) The entropy balance equation for Mixer A can be written as: ṁ 4s4 + Ṡ gen,MA = ṁ 5s5 + ṁ 6s6 (5.103) The exergy balance equation for Mixer A can be written as: ṁ 4ex4 = ṁ 5ex5 + ṁ 6ex6 + Eẋ dMA (5.104)

For Mixer B, the mass balance equation can be written as: ṁ 9 = ṁ 7 + ṁ 8 (5.105) The energy balance equation for Mixer B can be written as: ṁ 9h9 = ṁ 7h7 + ṁ 8h8 (5.106) The entropy balance equation for Mixer B can be written as: ṁ 9s9 = ṁ 7s7 + ṁ 8s8 + Ṡ genMB (5.107) The exergy balance equation for Mixer B can be written as: ṁ 9ex9 + Eẋ dMB = ṁ 7ex7 + ṁ 8ex8. (5.108) 5.5.5 Valve For the valve, the mass balance equation can be written as: ṁ 1 = ṁ 2 (5.109) The energy balance equation for the valve can be written as: ṁ 1h1 = ṁ 2h2 (5.110) The entropy balance equation for the valve can be written as: ṁ 1s1 = ṁ 2s2 + Ṡ genV (5.111) The exergy balance equation for the valve can be written as: ṁ 1ex1 + Eẋ d,V = ṁ 2ex2 (5.112) 5.5.6 Regulator For the regulator, the mass balance equation can be written as: ṁ 2 = ṁ 3 (5.113) The energy balance equation for the regulator can be written as: ṁ 2h2 = ṁ 3h3 (5.114) The entropy balance equation for the regulator can be written as: ṁ 2s2 + Ṡ genReg = ṁ 3s3 (5.115) The exergy balance equation for the regulator can be written as: ṁ 2ex2 = ṁ 3ex3 + Eẋ dReg. (5.116) 5.5.7 Heat exchanger The mass balance equation for heat exchanger 1 can be written as: ṁ 9 = ṁ 10 (5.117) 71

The energy balance equation for heat exchanger 1 can be written as: ṁ 9h9 + Q̇ in HX = ṁ 10h10+Q̇ loss HX (5.118) The entropy balance equation for heat exchanger 1 can be written as:

Q̇ in HX Q̇ loss HX ṁ 9s9 + + Ṡ genHX = ṁ 10s10 + (5.119) T0 T0 The exergy balance equation for heat exchanger 1 can be written as: T ṁ ex + (Q̇ − Q̇ ) (1 − 0) = ṁ ex + Eẋ . (5.120) 9 9 in HX loss HX T 10 10 dHX1 5.5.8 Energy and exergy efficiencies of the hybrid compressed air-electric prototype For the systems considered here, the energy efficiency can be defined as the ratio of useful energy output to the total energy input. The exergy efficiency is defined here as the ratio of useful exergy output to the total exergy input. In this, the energy and exergy efficiencies for the air motors, turbine, mixer, valve, regulator and overall system are defined and evaluated.

푊̇ 퐴푀 Ẇ AM Air motors: ηenAM= and ηexAM= (5.121) 푚̇ 5ℎ5 ṁ 5ex5 Ẇ T Ẇ 퐴푀 Turbine: ηenTA= and ηexAM= (5.122) ṁ 10h10 ṁ 10ex10 ṁ 4h4 ṁ 4ex4 PCM heat exchanger: ηenPHX= and ηex,PHX= T0 (5.123) ṁ 3h3+Q̇ in PHX ṁ ex +Q̇ (1− ) 3 3 in PHX T ṁ 10h10 ṁ 10ex10 Heat exchanger: ηenPHX= and ηex,PHX= T0 (5.124) ṁ 9h9+Q̇ in HX ṁ ex +Q̇ (1− ) 9 9 in HX T The energy and exergy efficiency of the overall system (Figure. 3.1) can be written as follows:

푊̇ 퐴푀1 +푊̇ 퐴푀2 +Ẇ 퐸푀1 +Ẇ T+Ẇ 퐸푀2 ηen,OV= (5.125) ṁ 2h2+Ẇ in battery+Q̇ in HX+Q̇ in PHX

푊̇ 퐴푀1 +푊̇ 퐴푀2 +Ẇ 퐸푀1 +Ẇ T+Ẇ 퐸푀2 ηex,ov1= T . (5.126) ṁ ex +Ẇ +(Q̇ +Q̇ )(1− 0) 2 2 in battery in HX in PHX T 5.6 Photovoltaic system The maximum power obtained from the photovoltaic system can be determined as follows:

푃푚 = 푉푚 × 퐼푚 (5.127) where 푉푚 is the maximum voltage and 퐼푚 is the maximum current. The useable exergy rate leaving the PV system is calculated as follows:

푇0 퐸푥̇푃푉 = 푉푚 × 퐼푚 − [(1 − ( )) × (ℎ푐 × 퐴 × (푇푐푒푙푙 − 푇0))] (5.128) 푇푐푒푙푙 where ℎ푐 is the convective heat transfer coefficient and defined as follows:

ℎ푐 = 5.7 + 3.8 푣 (5.129) 푚 where 푣 is the speed of the wind ( ). 푠 The maximum exergy rate entering the PV system due to the solar radiation is obtained as: 푇0 퐸푥̇ 푠표 = ( 1 − ) × 푆푡 × 퐴 (5.130) 푇푠표 푊 where 푆 is the global solar radiation in ( ) , and A is the PV area in (푚2). The main 푡 푚2 parameters considered in modeling the PV system are listed in Table 5.1.

Table 5.1: Data used in the parametric study for the photovoltaic model Parameter Value Cell operating temperature 46 °C Effective area 3 m2 Solar radiation 600 - 1200 W/ m2 Photovoltaic total output energy 16 kWh Temperature of the sun 5227 °C

5.7 Mechanical analysis The equation of motion for a vehicle in a longitudinal direction can be expressed as: du ∑ F − (F + F + F ) = M . (5.131) x RA RR RG d dt

Here, 퐹푥 refers to the tractive force, while 퐹푅퐴 . 퐹푅푅 . 퐹푅퐺 represent the air resistance, rolling resistance and gradient resistance, respectively. 푀푑 and 푢 are the vehicle dynamic mass and its longitudinal speed, respectively. Tractive force can be expressed as follows:

ηm×ηd× βi×βd Fx = × TICE(ωe) (5.132) rT where 휂푔 and 휂푑 refer to the gearbox transmission efficiency and differential efficiency, respectively. 훽 is the reduction ratio and subscripts 𝑖 and 푑 represent number a of gear ratio and differential, respectively, while 푟푇 is the tire radius. Air resistance, rolling resistance and gradient resistance can be calculated using the following equations: 1 F = ρ × C × A × u2. F = μ × W . F = W × sin (α ). (5.133) RA 2 a dr f RR V RG V road

Here, 퐶푑, 퐴푓, 푢 are the coefficients of drag, vehicle frontal area and vehicle speed, respectively.

휇푅 and 푊푉 훼푟표푎푑 are the rolling coefficient, vehicle weight and road gradient angle,

respectively. [68] Maximum vehicle speed can be obtained graphically by plotting the tractive force and the total resistance force versus the vehicle speed. The intersection point between the tractive force and the total resistance will represent the maximum speed. The maximum vehicle gradeability can be calculated as follows:

−1 ηg×ηd×β1× βd×TICEmax αroadmax = sin ( − μR). (5.134) rd×Vw 5.8 Aspen-plus simulation Simulations are performed with the aspen plus simulation software, which is commonly utilized in a wide range of industrial applications. In aspen plus, streams represent mass or energy flows. Energy streams may be defined as either work or heat streams, of which the latter also contain temperature information to avoid infeasible heat transfer. Aspen energy analyser examined systems and suggested changes that reduce energy costs. Thermodynamic properties are defined in the aspen plus libraries for air. The following simplifying assumptions are made in the analysis and simulations. The process occurs at steady state and isothermally and, in order to avoid kinetic affects, residence time is not considered. Ambient air is considered dried and on a volume basis as 79% nitrogen and 21% oxygen. Reference air temperature is 25 o c and pressure is 1 bar. During the processes, all the component pressure drops are ignored. The Peng– Robinson equation of state, with Boston-Mathias modifications, was used as the method for solving the equations. For a real gas, a correction factor, known as the polytrophic work factor, is introduced into the isentropic equation as:

(푛푠−1)⁄푛푠 푃1.푉1 푃2 푊푠 = 푓 ∙ 푛푠−1 [( ) − 1] (5.135) ( ) 푃1 푛푠 where f is the polytrophic work factor and ns is the isentropic volume exponent. For a real gas, the value of ns is not the same as k and is not constant. An average ns can be found by the correction factor adjusts WORKs for varying ns. The correction factor is defined as follows:

푙푛(푃2⁄푃1) 푛푠 = (5.136) 푙푛(푉1/푉푠) ℎ −ℎ 푛 −1 푓 = 푠 1 ∙ 푠 (5.137) 푃2푉푠−푃1푉1 푛푠 In effect, the correction factor f corrects for the application of a constant ns using the isentropic case as a reference point. Similarly, for a polytrophic process, the developed work becomes:

(푛−1)⁄푛 푃1.푉1 푃2 푊푝 = 푓 ∙ 푛−1 ∙ [( ) − 1]. (5.138) ( ) 푃1 푛 The average polytrophic volume exponent n is defined as:

푙푛(푃 ⁄푃 ) 푛 = 2 1 . (5.139) 푙푛(푉1/푉2) Again, variation of n affects works just as varying ns affects works. The same work correction factor is used. For isentropic compression, Wa (actual work) developed may be obtained by k applying P.V =constant to the work integral, assuming k= Cp/Cv to be constant along the path: (푘−1)⁄푘 푃1.푉1 푃2 푊푎 = 푘−1 ∙ [( ) − 1]. (5.140) ( ) 푃1 푘

The enthalpy changes and Wa are related by: 푊 ∆ℎ = 푠 (5.141) 휂 where, in this case, 휂 is the isentropic efficiency. The enthalpy change can also be obtained from the enthalpy hs at isentropic condition and the isentropic efficiency ns using the Mollier based method.

CHAPTER 6: RESULTS AND DISCUSSION This chapter presents the results of the experimental and theoretical investigation, and the modeling results of the 13 integrated energy systems. Resulting operating conditions for the process are applied in the all system models, and results are compared with those of the initial case study for systems. Finally, all systems are compared together and the best one is presented in terms of different views.

6.1 Experimental system results

Three different experimental prototypes and modeling results for compressed air car energy systems are given in the following order: Compressed air system with heating element; Compressed air system with PCM heat exchanger and three-hybrid compressed air-electric system. Eleven different pure and hybrid theoretical and modeling results for compressed air hybrid car energy systems are given in the following order: Compressed air only, Compressed nitrogen vehicle, Liquid nitrogen vehicle, Compressed carbon dioxide, Compressed air internal combustion and hydrogen vehicle, Compressed air internal combustion engine and compressed natural gas, Compressed air internal combustion engine and liquid propane gas vehicle, Internal combustion engine with compressed air system, Compressed air internal combustion engine with heat recovery and Internal combustion engine and compressed air with four-stage expansion.

6.1.1 Measurement uncertainties

Every measurement is susceptible to error and uncertainty. A measurement is the best quantitative estimate of an observation constrained by one or more limiting factors. The experimental measurements and calculated values are subject to device and statistical error that propagate within the results. Table 6.1 summarizes the error values for measurements associated with the primary devices used while conducting experiments for measuring and recording data. Furthermore, efforts to conduct different conditions for experiments in a consistent manner reduce additional random/rough errors. Testing situation placement of the prototypes is maintained, and, as far as possible, data with significant errors due to different conditions are re-taken under more consistent parameter conditions.

Table 6.1: Measurement uncertainties Variable Device Reference Bias error Relative Statistical Absolute value bias uncertainty uncertainty error (%) (%) (%) Potential Mastercraft 2 V 0.006 V 0.3 2.13 2.15 Multimeter/ clamp meter Current Mastercraft 2 A 0.012 A 0.24 1.30 1.32 Multimeter/ clamp meter Resistance Mastercraft 1 Ω 0.001 Ω 0.4 3.2 5 Multimeter/ clamp meter Weight High 0.1 g 0.01 g 0.09 0.67 1.24 Precision Lab Digital Scale Temperature Vernier 53 °C 0.5 °C 0.94 2.24 2.43 Temperature Sensor Dimensions Mastercraft 0.01 mm 0.001 mm 0.005 0.082 0.165 Digital Caliper Pressure Fluke 1 bar 0.01 bar 0.001 0.035 0.05 Pneumatic Pressure Gauge Rotational AGPtek 0.1 rpm 1 rpm 0.005 0.05 0.5 Speed Digital Laser Photo Tachometer Torque Generic YC- 1 Nm 0.01 Nm 0.2 2 2.2 AUS2 Measu Ratchet Measuring Digital Torque Tools

Compressed air has relatively low energy density. Air at 30 MPa contains about 50 Wh of energy per liter (and normally weighs 372 g per liter). In compressed air, prototypes tank designs tend to be isothermal. Figure 6.1 illustrates the prototype manufacturing process. The

compressed air system with a heating element is shown in 6(a) and (c) while 6(b) shows the compressed air system with the PCM heat exchanger. The hybrid compressed air-electric system can be seen in 6(d). The energy density of a compressed air system can be more than doubled if the air is heated prior to expansion. As shown in the picture, two different kinds of heat exchangers and heat elements are considered for heating the system’s air.

Figure 6.1 The prototypes manufacturing process showing: (a) Under compressed air system with heating element; (b) Compressed air system with PCM heat exchanger; (c) Above compressed air system with heating element; (d) Hybrid compressed air-electric system.

6.1.2 Compressed air system with heating element results

The energy and exergy efficiencies of Prototype 1 are assessed to be 59.5% and 51.0%, respectively. These results are presented in Table 6.2.

Table 6.2: Overall exergy and energy efficiencies of a compressed air system with a heating element Parameter Value

ηen, Prototype 1 59.5%

ηex, Prototype 1 51.0%

The exergy and energy efficiencies of the major components of Prototype 1 are calculated and shown in Figure 6.2. Maximum efficiencies are observed in the regulator, followed by the valves and the third highest efficiency occurs in Mixer A. To improve the performance of the overall system, efforts need to be made to increase efficiency in the turbine accordingly.

90 Energy efficiency Exergy efficiency 80 70 60 50 40

Efficiency(%) Efficiency(%) 30 20 10 0

Figure 6.2 Energy and exergy efficiencies of the components of prototype 1.

The exergy destruction rate for the major components of the first prototype is shown in Figure 6.3 where it can be seen that the highest exergy destruction occurs at the air motor and turbine. This might be the result of energy losses and fluctuating exergy content of compressed air energy in this prototype. Better air motor and air flow control could potentially minimize energy losses and, as a result, these exergy destruction values.

5% 8% 35% 9% Air motors Turbine Regulator Mixer A 13% Mixer B Valve

30%

Figure 6.3 Exergy destruction rates of major components of the first prototype.

Referring to Table 6.3, it can be seen that the major part of exergy destruction occurs in the Air motor 0.087kW and Turbine 0.074kW. Higher exergy destruction of the air motor and turbine is due to the irreversibility of compressed air expansion energy with big air consumption. The exergy destructions in Mixer A and Mixer B are not significantly different, at about 0.019 kW to 0.023 kW. The contributions of the valve in the total exergy destruction is comparatively small, at about 0.011 kW.

Table 6.3: Exergy destruction rates of the major components of prototype 1

Components Exergy destruction rates (kW) Air motors 0.087 Turbine 0.074 Regulator 0.032 Mixer A 0.023 Mixer B 0.019 Valve 0.011

Table 6.4 summarizes the experimental and theoretical state point properties of the compressed air system with a heating element. The agreement among theories compares the

experimental and theoretical temperature and pressure in all 14 state points. It can be seen that the theoretical and experimental temperature and pressure values are fairly close to each other. However, the magnitude of discrepancy varies from point to point. Energy system substance is dry air.

Table 6.4: Comparison results of experimental and theoretical state point properties of a compressed air system with a heating element State Model Model Prototype Prototype point pressure (kPa) temperature (K) pressure (kPa) temperature (K) [1] 34370 298 33440 293 [2] 34370 298 33440 293 [3] 33922 270 33440 267 [4] 758 282 807 278 [5] 710 284 807 282 [6] 710 284 807 282 [7] 710 284 807 282 [8] 710 284 807 282 [9] 455 258 248 262 [10] 455 258 248 262 [11] 455 258 248 262 [12] 455 258 248 262 [13] 434 282 248 278 [14] 96 260 97 263

Figure 6.4 shows a graph of pressure and temperature vs. state point. It can be seen that pressures from States 4 to 9 closely match and that, from States 9 to 13, theoretical amounts are slightly larger than the actual amounts. Due to the temperature vs. state point, theoretical temperature from the beginning up to State 8 is less than the actual prototype amounts and, from State points 9 to 14, the actual temperature is less than the theoretical results. The temperature increases with decreasing pressure in State points 5 to 8 through the heat exchanger.The pressure will then decrease dramatically after using the air motors. It can be seen that the experimental temperature and pressure values are very close to the theoretical temperature and pressure values.

303 34860 300 Model Pressure Prototype Pressure 32370 297 Model Temperature Prototype Temperature 294 29880 291 27390 288 24900 285 22410 282 19920 279

17430 276 Pressure (kPa) Pressure 14940 273 (K) Temperature 270 12450 267 9960 264 7470 261 4980 258 2490 255 0 252 1 2 3 4 5 6 7 8 9 10 11 12 13 14 State point

Figure 6.4 Comparison result of experimental and theoretical state point properties of the compressed air system with a heating element.

Table 6.5 indicates the prototype results for the compressed air system with a heating element that shows that the turbine work out will be 1.55 kW. Each air motor work will be 5.21 kW total work, and by four air motors will be 20.84 kW, which is perfect for the powertrain of a small-size city vehicle.

Table 6.5: Simulation results of the compressed air system with a heating element

Parameter Value ̇ 1.48 kW QINBattery ̇ 1.55 kW Woutturbine ̇ 5.21 kW WoutAir motor ̇ 191.5 N Fdragcruise Generated shaft work rate 20.84 kW

Figure 6.5 illustrates speed vs. time during the test process. Switching the powertrain from the Dynamometer system to the prototype occurred at 5km/h speed because of higher initial start torque. At 11 second test mode from the Dynamometer, the system changed to road mode. Subsequently after 59 seconds, the prototype reached 72.7 km/h. 100 90 80 70 60 50

40 Speed (km/h) Speed 30 20 10 0

Time (minutes)

Figure 6.5 Prototype acceleration 0-100 km/h on the Dynamometer test.

This means that the prototype acceleration 0-100 km/h is 150 seconds, which leads to a similar conclusion for all other compressed air vehicles where acceleration is a little low. Figure 6.6 shows force vs. speed with the real-time recorded draft force for four tires of Prototype 1

on the Dynamometer test. The major differences between minimal and maximal values of draft force in passings imply significant changes on the draft amplitude in time, which can be easily observed on the graph. The left front wheel has slightly higher force than the other three wheels because that corner weight is a little higher (25 kg) than the other corners due to having sandbags during the test.

770

760

750

740

730 Force Force (N) 720

710

Left Front Wheel Left Rear Wheel 700 Right Front Wheel Right Rear Wheel

690

Speed (km/h)

Figure 6.6 Real-time graph of recorded drag force for Prototype 4 tiers on the dyno test.

The lowest average value of draft was 690 N to 720 N, which was measured at the 4.2 km/h speed. The highest value for each wheel is between 710 N to 770 N. Figure 6.6 represents the compression force from low to high speed. The deviation sizes in thrust force depends on the ACE dynamometer setup. As observed, the thrust force and the fluctuation size in thrust force are the major influential parameters on the outputs, such as surface roughness.

7.00 58.50 6.50 54.00 6.00 49.50 5.50 45.00 5.00 40.50 4.50 36.00 4.00 31.50 3.50

27.00 3.00

Power (kW) Power Torque (N.m) Torque 22.50 2.50 18.00 2.00 13.50 1.50 9.00 Torque (N.m) Power(kW) 1.00 4.50 0.50 0.00 0.00

Rotational speed (rpm)

Figure 6.7 Prototype dyno graph, torque and power vs. air motor rotational speed.

As shown in Figure 6.7, the torque is measured in Nm and the power output is measured in kW. The left axis represents the power while the right axis is for the torque, with the X axis at the bottom showing the engine RPM. The dyno graph shows the power and torque of the prototype through the full rev-range at full airflow volume, overlaid on the same sheet to make the differences clear, with peak power and sometimes peak torque figure. The test runs on the dyno revealed that the air motors were producing a very flat power curve from 490 rpm to 800 rpm. The idea of this test and graph is to demonstrate how the compressed air vehicle will perform when accelerating. This clearly shows torque dropout after 1029 rpm and power dropout after 686 rpm. Peaks are 49.5 N.m between 538 to 784 rpm. The power drop off is not significantly high. The prototype, which typically responds very well to tuning, can reduce a good deal of the lapse in power at a lower rpm. The graph provides a roadmap to go fast as possible. By understanding how the peak, the power band, the area under the power curve and

the actual shape of the power curve affect performance, the air motors can be tuned to produce a curve that is optimized for drag, circuit, drift or street performance.

Figure 6.8 Prototype average tractive effort on the dyno test.

The details of the prototype test relative to the recorded average tractive effort vs. speed are seen in Figure 6.8, where it may be seen that the response prototype test accurately shows tractive force over the speed. tractive force measured by dynamometer test equipment on one tire. Slight variations occur due to response delays in the dynamometer force calculations, calibration settings, and the lack of filtering of the response signals prior to testing. However, integration of the average tractive effort results in reasonable variability between the actual and calculated values. As seen in Figure 6.8, the amplitude of change varies up to 160 N at a speed of 50km/h. The figure also shows that the amplitude of change varies around 60 N at a speed under 10 km/h and also shows the wheel motion on the dyno roll. The prototype will develop additional drag as it accelerates due to tractive forces, which increase with the square of the speed. Drag may also be produced at higher speed, which will increase the rolling friction between the wheels and rolls.

900 8

800 7

700 6 600 5 500 4 400 3 300

Road load force force load Road (N) 2 200 Road load force (N) (kW) power load Road 100 Road load power (kW) 1 0 0

Speed(rpm)

Figure 6.9 Road load force and road load power vs. vehicle speed.

The road load force and road load power vs. vehicle speed is shown in Figure 6.9. The coefficient of drag is determined to be 0.2, but this value is not completely accurate due to the test conditions. When the prototype speed changes between 630 rpm to 1575 rpm, the road load force has changed from 328N to 689N with an almost linear pattern. The rotational speed changes from 630rpm to 1575rpm while the road load power changes from 1kW to 7 kW, respectively.

6.1.3 Compressed air system with a PCM heat exchanger results

Energy and exergy efficiency of Prototype 2 are assessed to be 74.0% and 61.5%, respectively. The results are presented in Table 6.6. The exergy and energy efficiencies of the major components of Prototype 2 are calculated and shown in Figure 6.10. Maximum efficiencies are observed in the valve, followed by the regulator, while the third highest efficiency occurs in the air motors.

In order to improve the performance of the overall system, effort is needed to increase efficiency in the heat exchangers. Figure 6.11 represents the portion of the compressed air

system with the PCM heat exchanger main components in exergy destruction. As the figure shows, the heat exchangers are the most important exergy destructive components.

Table 6.6: Overall exergy and energy efficiencies of a compressed air system with a pcm heat exchanger Parameter Value

ηen, Prototype 2 74.0%

ηex, Prototype 2 61.5%

80 Energy efficiency Exergy efficiency 70

40 Efficiency(%) Efficiency(%) 30

Figure 6.10 Energy and exergy efficiencies of the selected units of Prototype 2.

Nevertheless, not much can be done to enhance the air motors’ exergetic performance as all the sources of irreversibility, i.e. air expiation and big air consumption for functioning air

motors and turbine. Referring to Table 6.7, the major part of exergy destruction occurs in the PCM heat exchanger 0.111kW and heat exchanger 0.098kW.

3%2% 1%

Valve 23% 19% Regulator PCM HX Turbine Air motors HX Mixer A 27% Mixer B 16%

Figure 6.11 Exergy destruction rates of major components of Prototype 2.

The next highest exergy destructions are the air motor and turbine with amounts of 0.067 kW and 0.036 kW. The exergy destructions in Mixer A and Mixer B are not much different, at about 0.012 kW to 0.009 kW. The contributions of the valve in the total exergy destruction is comparatively small at about 0.005 kW. Table 6.8 summarizes the experimental and theoretical state point properties of the compressed air system with a PCM heat exchanger.

Table 6.7: Exergy destruction rates of major components of prototype 2

Components Exergy destruction rates (kW) Valve 0.005 Regulator 0.081 PCM HX 0.111 Turbine 0.036 Air motors 0.067 HX 0.098 Mixer A 0.012 Mixer B 0.009

The agreement among theory compares the experimental and theoretical temperature and pressure in all 15 state points. It can be seen that the theoretical and experimental temperature and pressure values are fairly close to each other. However, the magnitude of discrepancy varies from point to point. Energy system substance is dry air.

Table 6.8: Comparison results of experimental and theoretical state point properties of the compressed air system with a PCM heat exchanger State Model Model Prototype Prototype point pressure temperature pressure temperature (kPa) (K) (kPa) (K) [1] 1034 298 1069 294 [2] 1034 298 1062 291 [3] 717 293 758 291 [4] 696 338 724 345 [5] 689 336 683 345 [6] 689 336 683 345 [7] 689 336 683 345 [8] 689 336 683 345 [9] 427 284 372 283 [10] 427 284 372 283 [11] 427 284 372 283 [12] 427 284 372 283 [13] 421 283 372 283 [14] 413 294 338 288 [15] 96 258 97 267

Figure 6.12 shows the pressure and temperature vs. state point and it can be seen that the pressures from States 1 to 15 dramatically decrease. The pressure levels of the States 1 to 4 prototype ae slightly higher than the theoretical levels but the State 5 to 14 actual pressures are slightly less than the theoretical pressures. Due to the temperature vs. state point, the theoretical temperature from State 4 to State 5 is higher than the actual prototype levels while for the other states the actual temperature is close to the theoretical results. The results of this system are summarized in Table 6.9.

1135 364 1045 350 955 336 865 322 775 308 685 294 595

280 Pressure Pressure 505 Temperature Model Pressure (kPa) 266 415 Prototype Pressure (kPa) 252 325 Model Temperature (K) 238 235 Prototype Temperature (K) 145 224 55 210 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 State point

Figure 6.12 Comparison result of experimental and theoretical state point properties of the compressed air system with a PCM heat exchanger.

Table 6.9, which indicates the prototype results for the compressed air system with a PCM heat exchanger, shows supplementary battery power is 2.18 kW and turbine work out will be 1.25 kW. Each air motor work will be 4.59 kW, hence total work by four air motors will be 18.36 kW, which is perfect for the powertrain of a small-size city vehicle. Figure 6.13 shows the temperature distribution of paraffin (candle), polyethylene glycol (Hot Pack) and alkane mix (antifreeze) enhanced PCM and TES materials at a specific point (measurement point).

Table 6.9: Simulation results of the compressed air system with a heating element Parameter Value ̇ 2.18 kW QINBattery ̇ 1.25 kW Woutturbine ̇ 4.59 kW WoutAir motor ̇ 175.3 N Fdragcruise Generated shaft work 18.36 kW

105 98 91 84 77 70 63 56 49 42 35 Temperature (℃) Temperature 28 Paraffin (Candle) 21 Polyethylene Glycol (Hot Pack) 14 Alkane mix (Antifreeze) 7 0

Time (s)

Figure 6.13 Temperature distribution of three different PCM and TES materials during a 36 minute period.

The graph shows that, for three different types of PCM and TES materials from the beginning of the heating process until 1170, 1300 and 1430 seconds, the temperature of the plain PCM and TES increases. In this case, there is sensible heat storage and the amount of heat stored depends on the specific heat of the PCM and TES in different phases, temperature difference and mass of material. The temperature of the PCM remains constant until 900 seconds, meaning that the PCM and TES are a heat source. The sensible heat is stored but, in this case, the amount of heat stored depends on the specific heat of the PCM in liquid phase. Due to much higher thermal conductivity, significantly less time is required for the ICE pack to heat and melt the PCM. Two different car radiator antifreezes have become extremely popular for keeping materials hot or cold during time. These antifreezes perform well and are non-toxic, non- flammable, environmentally friendly and easy to use.

44 40 36 32 28 24 20

Torque Torque (Nm) 16 12 8 4 7 bar 5.6 bar 4.2 bar 2.8 bar 0

Speed (rpm)

Figure 6.14 Torque vs. speed for Prototype 2 air motor on test table.

If a water-based PCM lower than 0°C is required, a salt can be added to the water to lower the freezing point. However, this significantly decreases the latent heat and broadens the melt/freeze temperature. Figure 6.14 shows torque vs. speed for the Prototype 2 air motor on a test table. The power that an air motor produces is simply the product of torque and speed. The air motor produces a characteristic power curve, with maximum power occurring from 600rpm to 1200rpm of the shaft speed. The air motor torque has significant changes in torques with the change of air motor inlet air pressure. The test is repeated at four different pressures, namely 7, 5.6, 4.2 and 2.8 bars. The amount of maximum torque fluctuates between 21 to 44N.m with changing shaft speed from 400 to 1300 rpm while the minimum torque fluctuates between 3 to 13N.m with changing shaft speed in the same range.

6.1.4 Hybrid compressed air-electric system results Energy and exergy efficiency of Prototype 3 are assessed to be 65.0% and 57.0%, respectively. The results are presented in Table 6.10. The exergy and energy efficiencies of the major components of Prototype 3 are calculated and shown in Figure 6.15.

Table 6.10: Overall exergy and energy efficiencies of the hybrid compressed air-electric prototype Parameter Value ηen, Prototype 3 65.0% ηex, Prototype 3 57.0%

The maximum efficiencies are observed in the electric motors, followed by the valve, while the third highest efficiency occurs in the air motors. To improve the performance of the overall system, efforts need to be made to increase efficiency in the heat exchangers. Figure 6.16 represents the portion of the hybrid compressed air-electric main components in exergy destruction. As the figure shows, the heat exchangers are the most important exergy destructive components.

100

90 Energy efficiency Exergy efficiency 80

40 Efficiency(%) Efficiency(%) 30

Figure 6.15 Energy and exergy efficiencies of the selected units of prototype 3.

Nevertheless, little can be done to enhance the air motors’ exergetic performance as all the sources of irreversibility, i.e. air expiation and big air consumption for the functioning air motors and turbine. Electric motors have the smallest exergy distractions. Referring to Table 6.11, the major part of exergy destruction occurs in the PCM heat exchanger 0.101kW and heat exchanger 0.099kW. The next highest exergy destructions are the air motor and turbine with amounts of 0.089 kW and 0.066 kW, respectively. The exergy destructions in Mixer A and Mixer B are not significantly different, at about 0.009 kW to 0.006 kW. The contributions of the electric motor in the total exergy destruction is comparatively small at about 0.004 kW. Table 6.12 summarizes the experimental and theoretical state point properties of the compressed air system with the PCM heat exchanger. The agreement among theory compares the experimental and theoretical temperature and pressure in all 11 state points. It can be seen that the theoretical and experimental temperature and pressure values are fairly close to each other. However, the magnitude of discrepancy varies from point to point.

2% 16% 22% Regulator 2% Valve PCM HX Mixer B 1% Turbine

22% Air motors Electric Motor 20% HX Mixer A 1% 14%

Figure 6.16 Exergy destruction rates of the major components of prototype 3

Figure 6.18 shows the pressure and temperature vs. state point. It can be seen that pressures from States 1 to 15 dramatically decrease from 1034kPa to 96kPa. There is a

significant discrepancy between the States 7 and 8 prototype and theoretical pressure levels, but the State 11 actual pressures are higher than the theoretical pressures.

Table 6.11: Exergy destruction rates of the major components of prototype 3 Components Exergy destruction rates (kW) Valve 0.007 Electric Motor 0.004 Regulator 0.073 PCM HX 0.101 Turbine 0.066 Air motors 0.089 HX 0.099 Mixer A 0.009 Mixer B 0.006 Due to the temperature vs. state point, the theoretical temperature in all states are a good match with the actual prototype’s state temperature results. Energy system substance is dry air.

Table 6.14 illustrates the PCM and TES substance properties and results.

1225 350 1135 336 1045 322 955 865 308 775 294 685 280 595

Pressure (kPa) Pressure 266 505 Model Pressure (kPa) (K) Temperature 415 Prototype Pressure (kPa) 252 325 Model Temperature (K) 238 235 Prototype Temperature (K) 224 145 55 210 1 2 3 4 5 6 7 8 9 10 11

Figure 6.17 Effect of ambient temperature on the overall energy and exergy

Table 6.12: Comparison results of experimental and theoretical state point properties of the hybrid compressed air-electric State Model Model Prototype Prototype point Pressure Temperature Pressure Temperature (kPa) (K) (kPa) (K) [1] 1034 298 1069 295 [2] 1034 298 1062 293 [3] 717 293 758 288 [4] 696 338 724 338 [5] 689 336 683 338 [6] 689 336 683 338 [7] 427 284 683 281 [8] 427 284 683 281 [9] 421 283 372 286 [10] 413 294 372 291 [11] 96 258 372 278

It allows comparisons between paraffin (candle), polyethylene glycol (Hot Pack) and alkane mix (antifreeze), and shows the amount of phase change temperature, melting enthalpy, latent heat capacity, and price per unit and temperature change, with giving the same amount of heat to substances in the same time duration. Paraffin has the highest phase change temperature and melting enthalpy with 89(◦C) and 240 (kJ/kg), respectively.

Table 6.13: Simulation results of the compressed air system with a heating element

Parameter Value ̇ 1.68 kW QINBattery ̇ 1.43 kW Woutturbine ̇ 7.10 kW WoutAir motor ̇ 4.46 kW WoutElectric motor ̇ 201.23 N Fdragcruise Generated Shaft Work (kWh) 23.12 kW

Alkane mix (antifreeze) is the most economical in comparison to the other materials. Paraffin and polyethylene glycol are PCM-based while the alkane mix car antifreeze is water- based. When testing all three substances in Prototypes 2 and 3, the overall compilation shows that paraffin has a better result due to the temperature (◦C) change with 1 kW/h.

Table 6.14: PCM and TES substance properties and results

PCM substance Phase Melting Latent Density Price Temperature change enthalpy heat (g/cm3 ) per (◦C) change temperature (kJ/kg) capacity unit ($) with 1 kW/h (◦C) (kJ/kg) Paraffin (candle) 89 240 151 0.77 2.5 16.5 Polyethylene 58 150 80.3 1.30 4 11.2 glycol (Hot Pack) Alkane mix N/A N/A 346 1 1.5 9.7 antifreeze)

By controlling the pressure and volume of the prototype tank, the speed of the prototype reaches from 0 to 70 km/h in 1.18 minutes. From minute 1.19 to minute 4.36, the prototype full tank completely depletes. A full tank with a pressure of 4650 psi and volume of 6.96 ft3 runs the prototype for 4 minutes and 22 seconds. The average speed is 38.78 km/h with the result that the built prototype can move up to 2.82 km with the indicated property values of the tank. Figure 6.19 shows that the 0-63 km/h acceleration time is 15 seconds. It can be seen that, after 15 seconds, the rear wheel speed is almost steady at around 65 km/h. It can control by current and much with front wheel air motors speed. The maximum current in armature is 347A. 80 72 64 56 48 40 32

24 Speed (km/h) Speed 16 8 0

Time (Minute)

Figure 6.18 Prototype tank depletion time vs. speed.

The top speed is predicted as 68.3 km/h. During the test, the battery voltage changes between 52V and 69v based on the measurement. As soon as the speed reaches about 20km/h, the battery requires amperage. The rear wheels are lowered, and the electric consumption during 17 seconds decreases as low as 94A.

73 347 324 66 301 59 278 255 Current (A) 52 232 Speed (km/h) 45 209 Voltage (V) 186 38 (V) Voltage and

Current (A) (A) Current 163 31 140 117 24 94 17 71

48 10 (km/h) Speed 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Time (s) Figure 6.19 Electric motor current, battery voltage and prototype rear wheel speed during acceleration time. 6.2 Simulation results

6.2.1 Introduction The software package of the Aspen-Plus is used to simulate all theoretical systems. For easier understanding of the subsequent diagrams, it is useful to give the legend for all components, as shown in Figures. In aspen plus, streams represent mass or energy flows. Energy streams may be defined as either work or heat streams, of which the latter also contain temperature information to avoid infeasible heat transfer. Mass streams are divided by aspen plus into three categories: mixed, solid, and non-conventional. Thermodynamic properties are defined in the aspen plus libraries for chemical components. Components present in the mixed and solid stream classes may participate in phase and chemical equilibrium and are automatically flashed by aspen plus at stream temperature and pressure. Non-conventional components are defined in aspen plus by supplying standard enthalpy of formation and the elementary composition (ultimate and proximate analysis including particle size distribution) of the components may also be defined. Although aspen plus calculates enthalpies and entropies for conventional 99

components, ambient temperature and pressure, which are required in evaluations of exergy. A property termed availability by aspen plus is calculated for conventional components.

6.2.2 Pure compressed air system results As can be seen from Figure 6.17, the proposed system is comprised of a car tank (CARTANK), a valve (VALVE), four expanders (EXP.) and three heat exchangers (HX). In a simulation design case study, it is first assumed that a vehicle tank, with a 300 liter capacity, will be filled with air at 350 bar with 25o C from a compressed air station.

Figure 6.20 Compressed air vehicle simulation schematic diagram.

The compressed air passes through the valve in order to reduce the pressure from 350 to 60 bar levels while keeping the inlet and outlet temperature at the same level, which gives pressure stabilization during operation. For this case, Points 3 and 4 represent the first expander inlet and outlet. The simulation parameters considered for the system are summarized in Table 6.15.

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Table 6.15: Simulation parameters for system 1

Four stage expansion assumptions Values Turbine mechanical efficiency (%) 95 Isentropic efficiency (%) 80 First stage input pressure (bar) 60 Second stage input pressure (bar) 22 Third stage input pressure (bar) 8 Output pressure (bar) 1 Expansion stages 4 Compression ratio 2.7

These parameters result from several trial-and-error simulations that were performed to determine the best system performance. The results are shown in Figures 6.18-6.20 and refer to produced mechanical energy vs. driving range and vs. air pressure, and the tank weight vs. pressure.

45 Powertrain indicator 40 0.4 0.5 35 0.6

0.7 Produced energy (MJ) Produced energy 30 0.8 1 25

20 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 Driving Range (km) Figure 6.21 Produced power vs. driving range

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80 Reheating @ 15oC 70 Reheating @ 30oC

Net Work Output (MJ) Output Work Net 20

0 350 400 450 500 550 600 650 700 750 800 850 900 Pressure (bar)

Figure 6.22 Work output vs. pressure assuming 300-liter storage tank

700 650 600 Tank 300 L 550 400 L 500 500 L 450 600 L 400 350 300

Tank Weight (kg) Weight Tank 250 200 150 100 50 350 400 450 500 550 600 650 700 750 800 850 900 Pressure (bar) Figure 6.23 Compressed tank weight change with different pressure and tank capacities

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6.2.3 Pure compressed nitrogen vehicle system results A case study can be seen in Figure 6.21, in which a compressed nitrogen vehicle simulation is analysed using the Aspen-Plus 7.0 simulation program. The graphical results are presented in Figure 6.22 in terms of network output vs. storage pressure. Several remarks can be made. Firstly, a 300 liter car tank is filled with compressed nitrogen with the property of 350 bar, 25 o C. Secondly, nitrogen flows through into the valve to reduce its pressure, meaning that the pressure will be reduced from 350 to 60 bar by using the valve to avoid pressure drop during operation in the proposed system. In the third step is, nitrogen passes through the first expander stage where pressure and temperature will be drastically reduced to 22 bar and -34 o C respectively. Fourthly, assuming summer conditions where ambient air temperature is high around 35 o C, a heat exchanger 1 (HX1) is considered in order to increase the temperature from -34 to 15 without adding any heat from outside sources. The expansion and heating processes repeat themselves until, finally, the nitrogen will become 1 bar, -47 o C. The resulting work can be seen from each expander of approximately 1.6 kWh, with a total 6.4 kWh.

Figure 6.24 Compressed nitrogen vehicle simulation schematic diagram.

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Figure 6.25 Network for the compressed nitrogen and compressed air via pressure

6.2.4 Pure liquid nitrogen vehicle system results

As can be seen in Figure 6.23, a liquid nitrogen power generation system has two main components, namely the expanders (EXP1, EXP2, VACUUM), and the heat exchangers (HX1, HX2, HX3, HX4, HX5, HX6, HX7, HX8), in addition to the three contributory components: the nitrogen tank, pump and comp1. The liquid nitrogen (L-N2) is pressurized at high pressure by pumping, and delivered to the heat exchanger HX1 where it is heated to 15 o C using the ambient air as the source of heat. Further, the nitrogen passes through HX2 where it is preheated to 50 o C before expansion in the EXP1. The heating supplied to the second heat exchanger is produced on board in compressor COMP1, which recompresses the nitrogen from a vacuum to atmospheric pressure. In the last stage, the nitrogen is expanded in a vacuum of 0.1 bar absolute where it reaches a temperature of -98 o C.

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Figure 6.26 Liquid nitrogen vehicle simulation.

19.5 Summer Winter 19

18.5

17.5

Net Work Output (kJ) Output Work Net 17

16.5

Pressure (bar) Figure 6.27 Network output via pressure for the different ambient temperatures.

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Furthermore, nitrogen is reheated to 15 o C, then compressed to 2 bar before expelling it out into the atmosphere. The temperature at the compressor outlet is 189 o C. Nitrogen is then cooled to 60 o C and the corresponding heat is recovered for inter-stage reheating at 50 oC. The heat recovery heat exchanger, which is indicated in Figure 6.23 as HX8, supplies heat to heat exchangers HX2, HX4 and HX6. Further results are shown in Figure 6.24 in terms of new work output vs. pump pressure in State 2. This result demonstrates that there is an optimum pressure that maximizes the mechanical work production by the system, which is around 275 bar acordingly. For summer conditions, the reheating with ambient air is assumed at 15 o C, while for winter conditions the reheating is assumed at 0 o C. The generated mechanical energy output with a liquid nitrogen tank of 300 litters is 18.5 MJ in winter and 19.5 MJ in summer. The difference between summer-winter is thus about 1 MJ, which means about 2 km of driving for a light vehicle. This result shows that external conditions marginally affect performance. The o mass of liquid N2 stored at 1 bar and -195 C in a 300 litter tank is 242 kg. Figure 6.25 presents the simulation result for a pressurized carbon dioxide vehicle. Specific to this system is that the carbon dioxide is in liquid phase in the storage tank and has to be throttled from 350bar to 40 bar to generate gas.

6.2.5 Pure compressed carbon dioxide system results

The temperature drops at 5o C in the throttling process; therefore, carbon dioxide is preheated with ambient air at 15 o C before expansion. The expansion process occurs in four stages and eventually the carbon dioxide is released at -31 o C. Hence, in summer operation it is opportune to cool the cabin for air conditioning with the expelled carbon dioxide, using a heat exchanger. Figure 6.26 presents the simulation results obtained with Aspen-Plus software for a storage tank of 300 liters. One can observe that, for 300 bar storage pressure, the produced mechanical energy to drive the vehicle is 40 MJ which, considering a powertrain indicator of 0.5 MJ/kg, corresponds to a maximum driving range of 80 km. However, the mass of the pressurized carbon dioxide in these conditions is high, namely ~300 kg.

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Figure 6.28 Compressed carbon dioxide vehicle simulation. 50 340 49 335 48 330 325 47 320 46

315 in tank (kg) tank in

45 2 310 44

305 Work output ( MJ)( output Work 43 300 ofCO Mass 42 Work output 295 41 Carbon dioxide mass 290 40 285

Storage pressure (bar) Figure 6.29 Driving range vs. work output for different energy consumption per km.

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6.2.6 Compressed air, internal combustion and hydrogen vehicle results System 5 in Figure 6.26 displays the simulation results for the system using compressed air combined with hydrogen as a fuel into the ICE. It can be observed that compressed air (State 3) and pressurised hydrogen are supplied to the ICE at 30 bar.

Figure 6.30 Compressed air + internal combustion + hydrogen vehicle simulation.

The ICE is simulated in Aspen-Plus as a system comprising a pressurized combustion chamber and a turbine for gas expansion (EXP1). The generated work output for the considered case is 16.4 kW. The driving range obtained with this amount of compressed air (300 liters) and H2 is 230 km. Energy consumption is under assumption of a powertrain indicator of 0.5 MJ/km, while the estimated driving range is 230 km.

Table 6.16: Hydrogen and air parameters determined for system 5

Parameters H2 Air Pressure (bar) 30 30 Temperature(oC) 25 25 Mole flow (kmol/h) 0.46 2.2 Mass flow (kg/h) 1.8 61

The main parameters for air and hydrogen as determined for System 5 are indicated in Table 6.16. The system efficiency is 53% without heat recovery from exhaust gases. If heat recovery

108

is applied to preheat the reactants, the efficiency is calculated at ~80% and the driving range increases to 380 km.

6.2.7 Compressed air, internal combustion engine and compressed natural gas results The results for System 6 are presented in Figure 6.27 and Table 6.17. The driving range obtained with this system for 0.5 MJ/km is 210 km. The operating pressure is set to 30 bar. The amount of heat that can be recovered from the exhaust gases is about 60% from the developed work.

Table 6.17: Main parameters of air and natural gas for system 7

Parameters CH4 Air Pressure (bar) 30 30 Temperature (oC) 25 25 Mole flow(kmol/h) 0.115 2.19 Mass flow (kg/h) 3.68 61.32

If this heat is to reheat the reactants, the driving range increases to about 50%. The amount of CNG consumed for the full range is ~7.5 kg, which is a consumption of 3.6 kg/100 km accordingly.

Figure 6.31 Compressed air + internal combustion engine + compressed natural gas.

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6.2.8 Compressed air, internal combustion engine and liquid propane gas vehicle

System 7 is similar to Systems 5 and 6, with respect to configuration, but uses a different fuel, namely LPG. The simulation results are shown in Table 6.18 and Figure 6.28. The driving range is 300 km with an LPG consumption of 2.5 kg LPG per 100km. The air tank is 300 liters at 350 bar (120 kg air) and the LPG tank is ~10 litres.

Figure 6.32 Compressed air + internal combustion engine + liquid propane gas.

Table 6.18: System 7 results

Parameters C3H8 Air Pressure (bar) 30 30 Temperature (oC) 25 210 Mole flow(kmol/h) 0.115 2.19 Mass flow (kg/h) 3.68 61.32

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6.2.9 Internal combustion engine and compressed air results

For Hybrid System 8, the considered fuel is gasoline. According to simulations, the driving range for 0.5 MJ/km is 220 km with a consumption of 2.2 liters of gasoline per 100 km. The assumed operating pressure is 40 bar and the exhaust gas heat is used to preheat the air before combustion. 7 100

4 10

3 Wnet Efficiency(%)

2 Efficiency Produced (kW)Power 1 1 0 10 20 30 40 50 60 70 80 90 100 110 120 Pressure (bar) Figure 6.33 Work output and thermal efficiency change for different operating pressures.

Figure 6.34 Compressed air + internal combustion engine simulation.

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The simulated parameters are shown in Figure 6.29. Additional results for System 8 are presented in Figure 6.30. It is studied the influence of operating pressure of the expanding air. As observed, if the pressure is increased to more than 40 bar, there is no significant gain in the produced work. For 40 bar pressure, the system efficiency is around 33%.

6.2.10 Compressed air and the internal combustion engine with heat recovery results

As described in Section 4, the ICE for this system is made to expel exhaust gases at 4 bar. The exhaust gases are then mixed with compressed air produced on board with a compressor with the purpose to increase the enthalpy. Further, the gases are expanded to the ambient pressure. It should be noted that this system does not carry a compressed air tank on board but rather is meant to recover the exhaust gas heat for increasing the system efficiency.

Figure 6.35 Compressed air, internal combustion engine with heat recovery system.

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The ICE engine efficiency is 29% and by application of the compressed air expander that recovers the enthalpy of exhaust gases to produce more work, the system efficiency increases to 32%. It is observed that the exhaust gas temperature is still high, but it cannot be utilized for more expansion because the pressure in State 9 (see below) is 1 bar. As a consequence of these results, this system was found inappropriate for implementation and will be dismissed for any further analysis.

6.2.11 Internal combustion engine and compressed air with four-stage expansion

This system has the highest range among systems investigated in this project. The simulated results are shown in Figure 6.32 and Tables 6.19 and 6.20. The best operating pressure was found to be 60 bar and air expansion is performed in four stages, with reheating to 300o C. An advanced heat recovery system has been designed for better efficiency of work generation.

Table 6.19: System 10 inlet-outlet conditions

ICE engine section Pneumatic air motor Section Parameter Inlet Outlet Inlet Outlet Mass Flow (kg/hr) 25 0 194 42 Mole Flow (kmol/hr) 0.22 0 7.0 0 Volume Flow (liters/hr) 34 0 716 78 Air for IC (kmol/hr) 5.3 0 - - Gasoline for IC (kmol/hr) 0.043 0 - - Temperature (oC) 25 1100 25 25 Pressure (Bar) 50 1 40 1 Tank Pressure (Bar) 1 1 250 40 Operating Pressure (Bar) 50 1 40 1

This system consumes 4.6 liters of gasoline per 100 km. The benefit of this system is that it can drive 200 km with 6.5 liters of gasoline operating in hybrid mode. This operation is less polluting and suitable for towns and cities. After 200 km, the reserve of compressed air is used up and the vehicle can drive on gasoline mode with a consumption of 7.5 liters per 100 km. The compressed air is stored at 250 bar in tanks, amounting to 872 liters and weighing 236 kg.

113

Figure 6.36 Compressed air + internal combustion engine simulation

114

Table 6.20: Simulation results for system 10

Work Values ICE work (kWh), WICE 16.2 Hybrid operation Air work (kWh), WAIR 19.8 Total (kWh), WICE+WAIR 36 Only ICE operation (kWh) 64 Total shaft work (kWh) 100 Exhaust gas heat recovery (%) 30 Efficiencies ICE efficiency (%) 28 Air motor isentropic efficiency (%) 80 Air motor mechanic efficiency (%) 95 Total system efficiency (%) 32 Specific transmission energy (MJ/km) 0.63 Air contribution (km) 113 Hybrid operation: Air (716 liters) + Gasoline contribution (km) 93 Gasoline (6.8 liters) Total (km) 206 Gasoline-only contribution (27.2 liters) 366 Total Expected Driving Range (km) 572 Fuel Consumption 3.3 liters/100 Gasoline (6.8 liters) km Hybrid operation 288 liters/100 Air (716 liters) km 7.5 liters/100 Gasoline (27.2 liters) km Specific Fuel Cost Air (716 liters)+Gasoline (6.8 liters) 6.4 cents/km Gasoline (27.2 liters) 8.1 cents/km Specific CO2 emissions Specific emission ( gCO2/MJ gasoline) 71 Air emission (g CO2/MJ shaft) 22 Hybrid operation Gasoline emission, (g CO2/MJ shaft) 116 Total (g CO2/MJ shaft) 138 Only ICE operation (g CO2/MJ shaft) 260 g CO / MJ shaft 216 Total GHG emission 2 g CO2 / km 136

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6.3 Compressed gas maximum work

Let us assume an insulated thermodynamic system, comprising a fluid that is not in thermo- mechanical equilibrium with the environment at standard reference temperature 푇0 and reference pressure 푃0. There are two limiting cases to consider here:

 The fluid is a gas at elevated pressure 푃 ≫ 푃0 and the same temperature as the

environment푇 = 푇0. This case is representative for a compressed air vehicle.

 The fluid is a liquid at cryogenic temperature 푇 ≪ 푇0 and about the same pressure as the environment. This case is representative for a liquid nitrogen vehicle.

The maximum mechanical energy, that is, the exergy that can be extracted from such a fluid in thermo-mechanical non-equilibrium with the environment, can now be analyzed. This is a non- flow exergy, which for 1 kg of substance is:

퐸푥 = (푢 − 푢0) + 푃0(푣 − 푣0) − 푇0(푠 − 푠0). (6.3)

Under the assumption of ideal gas, the internal energy difference 푢 − 푢0 is nil. Using entropy equations and the ideal gas equation of state, (6.3) becomes:

1 퐸푥 = 푅푇 [ln(PR) + − 1] . (6.4) 0 PR

If one denotes 푉 the volume of the reservoir and 푚 the initial mass of gas, one can introduce the following dimensionless exergy expression that is known as exergy ratio:

푚퐸푥 ER = . (6.5) 푃0푉

The exergy ratio then becomes:

1 ER = PR [ln(PR) + − 1]. (6.6) PR

This gives the opportunity to estimate the upper bound of mechanical energy that can be obtained from a compressed gas reservoir of 1 cubic meter (or 1000 liters), assuming that all exergy can be converted to useful mechanical energy. As an example, assuming a powertrain indicator of 0.5 MJ shaft mechanical energy per km driven, if the initial pressure in the tank is 100 atm (PR = 100), the exergy content is 46.6 MJ per 1000 liters and the driving range is 93.3

116

km; if instead the storage tank is of 500 liters, the driving range is reduced to half, that is 46.5 km. At 350 atm initial pressure and with a 500 liter tank, the upper bound of the driving range is around 200 km. For a tank of 100 liters and 800 bar pressure, the driving range would be about 100 km, which is five times less than that of an economic gasoline vehicle. In order to achieve a 500 km range with a 1000 liter tank, the initial pressure must be 410 bar.

The exergy content of a compressed air tank has been calculated as a first approach based on ideal gas assumption according to the curves presented in Figure 6.11. These approximations are only indicative; no practical design of a compressed air vehicle will be able to achieve the upper bound thermodynamic values (the exergy content). Therefore, the curves indicating the driving range give larger values than the expected driving range of actual designs. It is thus important to determine the technically realizable figures regarding the produced shaft energy from a compressed gas tank and the associated driving range.

Regarding the exergy content of compressed gases, more accurate estimations can be achieved using advanced equations of state. The Engineering Equation Solver software [62] is used in this report in order to determine the exergy content of compressed air, compressed nitrogen and pressurized carbon dioxide (all these three fluids being kept in storage tanks at ambient temperature assumed to be 25oC). Cryogenic nitrogen at -195o C and liquid carbon dioxide at -50oC were also considered. For the compressed air, the equation used is that in [63], which is one of the fundamental equations of state for the gas mixture composed of air, which is valid up to pressures of 2 GPa. For nitrogen, the used equation of state is that used in [65], valid also up to 2 GPa. For carbon dioxide, the fundamental equation of state in [66] is used. The results are graphically presented in Figures 6.12-6.14. The calculated exergy per unit of volume in function of the dimensionless pressure ratio PR is shown in Figure 6.12, which also shows an interesting result, namely, that at ambient temperature, the exergy stored per unit of volume is the highest for carbon dioxide at lower pressures while it is the lowest at higher pressures. Among all considered cases, the exergy stored in cryogenic nitrogen is the highest. This result can be better understood if the specific exergy (gravimetric) and the density of the respective pressurized gases are simultaneously analysed, as indicated in Figures 6.13 and 6.14, respectively.

117

700 Ex''' 1400

e Driving range @ 0.5 MJ/km r 600

Driving range @ 1.0 MJ/km 1200

0 Driving range @ 1.5 MJ/km 0 500

r 1000

J 400

, 800

E 300 600

200 400

Driving range, km per 1000 litres 1000 per Drivingkm range, 100 200

0 0 200 400 600 800 1000 PR Figure 6.37 The exergy content and ideal maximum driving range of a vehicle operated with compressed ideal gas.

The compressed nitrogen and compressed air have approximately the same behaviour. The specific energy density of carbon dioxide is about three times lower than that of these gases. However, the density of carbon dioxide is higher than that of compressed air or compressed nitrogen. This is the case because the pressurized carbon dioxide is in liquid form. At lower pressures, the density of pressurized carbon dioxide is more than four times higher than that of compressed gases. This explains why, at lower pressures, the volumetric specific exergy of carbon dioxide is about three times higher than that of the other compressed gases. However, at higher pressures (e.g., 1000 atm) the density of compressed air and nitrogen is about half of carbon dioxide. This translates in a slightly higher volumetric specific exergy of nitrogen and air vs. carbon dioxide; for example, at 1000 bar, the volumetric energy density of carbon dioxide is 348 MJ/m3, while that of nitrogen is 384 MJ/m3. It may be concluded that, for moderated pressures (considered from 100 atm up to about 400 atm), the carbon dioxide is the preferred medium for thermo-mechanical energy storage (among all three analysed gases).

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1000

/ J 800

g Cryogenic N2 @-195°C

x Liquid CO2 @ -50°C

600

i Carbon dioxide

c Nitrogen

s Air

i 400

V 200

0 0 200 400 600 800 1000 PR Figure 6.38 Volumetric specific exergy of pressurized air, nitrogen and carbon dioxide. (Note: If not indicated otherwise, the storage temperature is 25oC.)

With a tank of 100 liters pressurized at 200 atm, the following results are obtained:  For carbon dioxide: exergy content 21 MJ, weight 92 kg, displacement 41 km;  For nitrogen: exergy content 10 MJ, weight 22 kg, displacement 20 km.

In the above example, the weight is that of the pressurized fluid only (the tank itself is not considered) and the vehicle displacement is calculated for 0.5 MJ/km, assuming the extreme situation when all the stored exergy can be used for propulsion. These results suggest that, for the assumed conditions, the driving range with pressurized carbon dioxide is higher than that with compressed nitrogen or air. Furthermore, it is observed that compressed nitrogen is slightly more advantageous in terms of exergy content than compressed air. Pressurized carbon dioxide as a medium for thermo-mechanical energy storage per unit of volume thus appears attractive. Carbon dioxide can be obtained from GHG emitting industries such as fossil fuel power plants or cement industries, or from biomass combustion.

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1.0

0.9 Cryogenic N @-195°C 0.8 2

0.7

0.6

0.5 Nitrogen Air 0.4 Liquid CO2 @ -50°C

Specific exergy, MJ/kg Specificexergy, Carbon dioxide 0.3

0.2

0.1 0 200 400 600 800 1000 PR Figure 6.39: Specific exergy of pressurized air, nitrogen and carbon dioxide. (Note: If not indicated otherwise, the storage temperature is 25oC).

Hence, this carbon dioxide can be considered either as GHG-free gas (when sourced from biomass) or a lower-greenhouse effect gas (when saved from fossil fuel combusting facilities or cement factories). However, it can be observed that the density of carbon dioxide is the highest among the investigated fluids (see Figure 6.14). As a result of the high density, the energy thermo-mechanical energy content stored in pressurised carbon dioxide is the lowest among all studied options (see Figure 6.13). It should also be noted that the storage of carbon dioxide is made in liquid form. Therefore, an expansion vessel must be placed on the vehicle to compensate for thermal expansion of the liquid. As a consequence, one may expect that the equipment on board a vehicle that is propelled with pressurized carbon dioxide will have substantially larger volume than the effective volume of the storage tank. In comparison, compressed air storage may be found to be simpler, needing only a tank and a pressure regulator. The above results are graphically summarized in Figure 6.15, which shows the specific gravimetric exergy on the abscissa and specific volumetric exergy on the ordinate.

120

1400

1200

1000

800

n Liquid CO2 @ -50°C e 600

D Carbon dioxide Cryogenic N2 @-195°C 400 Air Nitrogen 200

0 0 200 400 600 800 1000 PR Figure 6.40: Density of pressurized air, nitrogen and carbon dioxide.

Figure 6.41 Specific exergy stored in pressurized carbon dioxide and in compressed air and nitrogen.

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6.4 Compressed gas storage optimization The exergy content of the compressed air storage and the retrievable mechanical work are calculated assuming isentropic expansion of compressed ideal gas in single stage. The results are reported in Figure 6.16, on which is plotted the exergy efficiency of the expansion defined according to:

WR 휂푒푥 = . (6.7) ER

5 5 7 PR− PR7+1 2 2 휓 = 1 . (6.8) PR푙푛 (PR+ −1) PR

The exegetic efficiency curve is superimposed on the same figure and shows a maximum at an optimum value of the PR. The optimum can be obtained by differentiating (6.8) with respect to the PR , which gives:

2 푑휂푒푥 2 ln(PR)−7PR7+7 = . (6.9) 푑PR 9 7PR7 ln2(PR)

Solving 푑ηex/푑PR = 0 is equivalent to solving:

2 2 ln(PR) + 7 = 7PR7. (6.10)

Here, the solution of (6.10) is PRopt = PRopt = 26.03 for which 휂푒푥max = 70% (see Figure 6.16). This is an interesting result with practical relevance, which shows that there is an optimal storage pressure that maximizes the work retrieved per unit of volume with respect to the stored work potential (i.e., the exergy). At pressures that are higher than optimum, the exergy efficiency drops; for the ideal gas case it drops about 13% when pressure increases from 26 atm to 1000 atm. Nevertheless, choosing the optimum pressure in the storage tank of a pneumatic vehicle, as identified here, is a matter of thorough thermo-economic analysis. The energy balance for the overall process, considering four-stage compression to 350 atm at the air compression station followed by four-stage expansion with reheating on vehicles, has 31% efficiency. The calculated efficiency of the compression and expansion process is assumed isentropic (ideal).

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Figure 6.42 Work ratio, exergy ratio and exergetic process efficiency of work generation from compressed ideal gas. For 70% assumed isentropic efficiency, the efficiency becomes around 17%. The overall efficiency is calculated as the ratio between the shaft energy available on board for propulsion and the electric energy consumed to compress the air. Figure 6.17 shows the energy breakthrough for the overall compression-expansion process on a pneumatic vehicle for 350 atm storage pressure, assuming ambient conditions at 25oC. 50

40 Isentropic 70% Isentropic efficiency

20 Efficiency (%) Efficiency 10

0 Heat dissipated in the ambient Work loses Power for onboard uses Available shaft energy

Figure 6.43 Overall energy breakthrough for the pneumatic vehicle considering both phases: air compression at charging stations and air expansion on the vehicle. Four-stage compression and expansion. Storage pressure 350 atm.

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6.5 Comparison of systems In this section, a comparative study is conducted between the excremental and proposed theoretical integrated system to identify which is more efficient and cost effective, and to determine the exergy destruction rates associated with each system.

6.5.1 Comparison of experimental systems In Table 6.21, three prototypes are compared. As shown, the compressed air system with a PCM heat exchanger has the furthest driving range but has the lowest generating shaft work with an amount of 18.36kW. The hybrid compressed air-electric system is the most powerful prototype with generating shaft work of 23.12kW. The compressed air system with a heating element prototype uses less energy to heat up cold air due to using heating elements instead of a PCM heat exchanger, hence loses more energy than others due to exergy efficiency.

Table 6.21: Comparison of the three built and tested prototypes

Systems Considered Compressed air Compressed air Hybrid system with system with compressed air- heating element PCM heat electric system exchanger ̇ 1.55 kW 1.25 kW 1.43 kW Woutturbine ̇ 5.21 kW 4.59 kW 7.10 kW WoutAir motor ̇ 191.5 N 175.3 N 201.23 N Fdragcruise ̇ 1.48kW 2.18 kW 1.68 kW QINBattery ηen, Prototype 59.5% 74.0% 65.0% ηex, Prototype 51.0% 61.5% 57.0% Start Operating Pressure (kPa) 807 758 758 Generated Shaft Work (kWh) 20.84 kW 18.36 kW 23.12 kW

In Table 6.22, 3 prototypes are compared with pneumatic cars in the market. As it shows driving range of Prototype 2, with 140 km and high efficiency as good as 74% is very higher than the other comparable. The prototypes have lots of advantage and will be successful in comparative market.

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Table 6.22: Comparison of 3 prototypes with compressed air cars 1, 2 and 3 Criteria Prototype Prototype Prototype MDI AIR MDI One MDI City system 1 system 2 system 3 Pod Vehicle cost ($) 9,000 12,000 14,000 8,000 25,000 18,000 Weight (kg) 750 850 900 380 800 550 Maximum 20.84 18.36 23.12 14 25 14 power (kW) Top speed 70 100 120 98 131 110 (km/h) Driving range 128 140 131 135 165 127 (km) with full tank fuel Time required 4.6 3 3 2 4 2 to fill tank in station (minutes) Charge on 5 4 4 3 6 3 electric plug (h) Cost to refill 0.032 0.032 0.032 0.028 0.038 0.028 vehicle ($/km) Acceleration 7.4 7.4 3 10.2 7.4 5.5 time: 0-100 km/h (sec) Efficiency (%) 60 74 65 43 60 60 Number of 4 4 4 5 6 3 passengers

6.5.2 Comparison of Simulated Systems It should be noted that it is not possible to use all the compressed air in the tank since the operation pressure is 40 bar, meaning that, when the pressure level drops to 40 bar in the tank, amounting to 716 liters, there is no pressure difference to drive the operation between the storage tank and the expanders. Thus, 716 liters can be usable in this particular case. The average efficiency of the ICE is 28% and, in hybrid mode, the system efficiency becomes 32%.

The average GHG emissions is 107 g CO2 equivalent per km. It should be noted that, as

mentioned above, the average Canadian car emits about 131 g CO2. The cost of driving for the hybrid mode is 5.1¢/km and 6.4¢/km for the gasoline only mode. A comparison of the studied systems is shown in Table 6.24, which illustrates the results for the pure and hybrid systems in terms of operating pressure, shaft work, fuel consumption, GHG emission, fuel cost and

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expected range. In the pure category section, the best configuration seems to be CCO2, since compressed CO2 has a higher density than compressed air, with an expected driving range of 80 km. Moreover, fuel cost is relatively lower than compressed air, while GHG emission is higher.

Table 6.23: Simulation parameters for system

Parameters Values Ambient temperature 25 oC Pressure 350 bar o Liquid N2 temperature -195 C Tank size 300 litters Turbine mechanical efficiency 95 (%) Isentropic efficiency 80 (%)

Note that producing compressed air has the advantage of consuming less energy than producing CN2 and LN2 makes compressed air more favorable. It should also be highlighted that compressed air proves that it can be an alternative fuel, with a driving range of 56 km. In the hybrid category, the results show that System 6 has the superior design and implementation, having a high driving range and relatively lower GHG emission. System 6 also has the lowest fuel cost per kilometer. The simulation parameters are summarized in Table 6.23.

Table 6.24: Comparison of considered pure systems

Systems Considered CA CN2 LN2 CCO2 Operating Pressure (Bar) 60 60 30 40 Generated Shaft Work (kWh) 7.7 6.4 5.1 11.1 Fuel Consumption (litres/km) 5.5 6.5 8.1 3.8

GHG Emission (gCO2/km) 98 100 110 103 Fuel Cost (cents/km) 4 3.5 4.0 3.5 Expected Driving Range (km) 55 46 37 80 Estimated Vehicle Cost ($) 10,000 10,000 12,000 13,000

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Table 6.24: Comparison of considered compressed air + conventional fuel hybrid

Systems Considered CA+ICE CA+ICE CA+ICE CA+ICE CA+ICE CA+ICE + H2 +CNG +LPG 1 stage 4 stage Operating Pressure (Bar) 30 30 30 40 ICE-50 ICE- 50 Air-4 Air-40 Shaft Work (kWh) 16.4 28 38 31 12 36

Fuel Consumption 0.03 H2, 0.036 0.025 0.022 0.035 0.033 (litres/km) 1.30 Air CNG, LPG, Gasoline, Gasoline, Gasoline 1.5 Air 1.5 Air 1.5 Air 1.8 Air 2.88 Air

GHG Emission 98+H2 98+CNG 98 98+ 98+ 136 (gCO2/km) Fuel Cost (cents/km) 7.3 9.5 8.5 6.8 7.8 6.4 Driving Range (km) 230 210 280 220 86 206 Estimated Vehicle Cost 40,000 20,000 18,000 17,000 17,000 20,000 ($)

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CHAPTER 7: CONCLUSIONS AND RECOMMENDATIONS 7.1 Conclusions Compressed air is an active area of research in green methods for vehicle powering options. Much of the theoretical experimental research focuses on characterization and comparison of different prototype system components under ideal laboratory conditions on a small scale. The present study develops and tests three fully integrated prototype systems: a compressed air system with a heating element prototype; a compressed air system with a PCM heat exchanger prototype; and a hybrid compressed air-electric system prototype. All three theoretical case study systems are analysed using energy and exergy approaches together with a parametric study to identify the effect of varying different designing and surrounding parameters on the performance of the introduced systems and comparing the prototypes results. Furthermore, ten novel integrated energy systems are conceptually developed to function as a potential powering option for vehicle applications.

 The energy efficiencies for prototype systems 1, 2, and 3 are found to be 59.5%, 74.0%, and 65.0%, respectively while the exergy efficiencies are 51.0%, 61.5%, and 57.0%, respectively.

 The predicted driving ranges for systems 1, 2, and 3 are 128 km, 140 km, and 131 km, respectively and the highest shaft work is generated in system 3. The generated shaft work of systems 1, 2, and 3 are 20.84 kW, 18.36 kW, and 23.12 kW respectively.  The liquid nitrogen (cryogenic) system is better than the compressed air and compressed nitrogen systems, since it is able to develop 7 MJ of mechanical energy for propulsion from a 100-liter storage tank.  The pressurized carbon dioxide shows the maximum driving range among all pure systems studied, with 14 MJ/100 liters when pressurized at 300 bar.  The compressed air systems with four reheating stages can develop up to 3 MJ for a 100- liter tank with storage at 350 atm.  When applied in Canada, because of low electricity grid GHG emissions, the compressed gas vehicles make better sense as they emit less GHG than the conventional ICE based passenger cars.

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7.2 Recommendations This study recommends a demonstration study as an important strategic step in testing the efficacy of a hybrid pneumatic model as an alternative to prevailing powertrain paradigms. Based on the results delivered in this study, for future studies it is recommended:  To build prototypes for the ten theoretical proposed vehicle systems is essential in order to investigate and compare their actual performances with the results obtained from the current thermodynamic analysis. Building prototypes is also necessary since it can motivate the automotive industry to promote the proposed systems to the commercialization stage.  To comparatively assessment of PCM options, with a better design for maintaining constant heat under various driving conditions, should be conducted. Additional investigation into possible heat recovery options for the proposed systems should be studied.  To investigate system hybridization possibilities should be investigated with different fuel powering options such as fuel cells, battery electric vehicles, and ICEs. Supplementary studies of the control mechanism of each individual wheel with compressed air flow should be conducted.  To design improvement studies, including weight and volume reduction, should be performed, to reduce the space demand in the vehicle. System scalability should be investigated in more detail to provide solutions for heavy duty vehicles.  To apply waste heat recovery to these cycles and used for cogeneration purposes or, better, converted into recovered work through heat engines. In this way, the compression efficiency is increased because the compression work may approach with at least 10% more than the isothermal version.  To utilize the multi-level heat exchanger network partly embedded in the vehicle body for collecting heat associated with solar radiation when available; a phase change heat fluid can be circulated at low pressure to transfer the heat to the pressurized expanding air.  To implement regenerative braking for air tank re-pressurization through pneumatic- hydraulic systems, which can operate in reverse as air compressors. Essentially, at the first stage of expansion of the air motor, the use of a hydraulic-pneumatic expander/compressor is recommended since this kind of device can operate over large pressure differentials (which characterize the first stage of expansion). 129

 To investigate the possibility of storing cold or heat onboard for later regenerative use; e.g., cooling the air before compression at braking time, or heating the air before expansion during acceleration. Such strategies will increase driving range.

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