THE EFFECT OF OXYGEN-ENRICHED AIR ON THE PERFORMANCE AND EXHAUST EMISSIONS OF INTERNAL COMBUSTION ENGINES by VARADARAJA SETTY, B.E. A THESIS IN MECHANICAL ENGINEERING
Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN MECHANICAL ENGINEERING
Approved
Accepted
May, 1993 ACKNOWLEDGEMENTS
I am deeply indebted to my advisors Dr. Timothy T. Maxwell and Mr. Jesse
C. Jones for their superb technical advice, understanding, and patience in helping me to solve \'arious problems during the course of this work. I am equally indebted to
Dr. Raghu Narayan for his support and active involvement in this project.
I would like to thank Mr. Don Boone whose selfless effort and past experience helped me to expedite the completion of this work. I thank Mr. Patrick Nixon,
Mr.Christopher Boyce, and Mrs. Carmen Hernandez for their ideas and timely assistance. I also thank Mr. Norman L. Jackson, Mr. Lloyd Lacy, and Mr. John P.
Bridge for their help during the experimental work.
I am highly grateful to my parents Mr. Narayan Setty and Mrs. Gangamma
Narayan Setty for their loving support and constant exhortation as well as other family members who provided encouragement and prayer. Finally, I would like to thank my roommates and friends for their help and support during this project.
11 TABLE OF CONTENTS
ACKNOWLEDGEMENTS 11
ABSTRACT v
LIST OF TABLES Vl
LIST OF FIGURES Vlll
CHAPTER 1
I. INTRODUCTION 1
The Future of Automobile 1
Factors Influencing the Formation of Exhaust Emissions 4
The Importance of Oxygen Enrichment 7
II. LITERATURE SURVEY 13 ill. OBJECTIVES 16
Project Objectives 16
Thesis Objectives 16
IV. TEST EQUIPMENT 17
General Plan 17
Modified Test Engine 18
Fuel Injection System 22
The Injector 22
Injector Control Mechanism 22
Water Dynamometer 26
Air Flowmeter 27
111 Mass Flowmeter for Compressed Natural Gas 27
Oxygen Sensor 30
Exhaust Gas Analyzer 32
Data Acquisition System 32
V. TEST PROCEDURE 33
Calibration 33
Preliminary Tests 39 Gasoline Tests 39
Compressed Natural Gas Tests 41
VI. TEST RESULTS 42
Brake-horsepower 42
Exhaust Gas Temperatures 46
Brake Specific Fuel Consumption and Fuel Conversion Efficiency 46
Volumetric Efficiency 57
Exhaust Emissions 60
Tests Results with Gas Separator 60
VII. CONCLUSIONS 71
Conclusions 71
Suggestions for Future Research 72
REFERENCES 73
APPENDIX
A. BASIC COMPUTATIONS 75
B. THEORETICAL AIR CALCULATION 77
IV ABSTRACT
Automobiles and trucks consume a major portion of the energy used for transportation in the US. They generate a significant amount of the emissions that contribute to air pollution. During the past few years, research on cleaner burning alternate fuels has been aimed at improving engine efficiencies and decreasing emissions that pollute the environment. Methanol, LPG, and natural gas have emerged as the leading alternative fuels; however, several problems must be solved before these fuels can be considered as true replacements for gasoline.
This research was devoted to the study of the performance of I. C. engines with enriched oxygen air fueled by gasoline and natural gas and to study the feasibility of gas separator to supply oxygen enriched air for vehicle applications. A single cylinder, 4-stroke, spark-ignition engine was used in the program to evaluate the effect of enriched oxygen air on engine performance and exhaust emissions. The oxygen content in the intake air was varied between 21% and 25%. The effects of oxygen enrichment are reviewed in terms of volumetric efficiency, power output, specific fuel consumption, fuel conversion efficiency, exhaust gas temperature, and exhaust emissions (carbon monoxide and hydrocarbons). Test results indicate that the use of oxygen enriched air results essentially in a significant increase in power output, improved thermal conversion efficiency, a substantial reduction in carbon monoxide and hydrocarbons and a decrease in volumetric efficiency.
v LIST OF TABLES
1.1 Total Annual U.S. Emissions from Artificial Sources 2
1.2 Total Exhaust Emissions per kg. Fuel Burned in S.I. Engines 2
1..3 Hydrocarbon Composition of S.I. Engine Exhaust, Percent of Total HC 9
.f.1 Test Engine Specification 20
5.1 Test Conditions 40
6.1 Percentage Increase in Power with Oxygen Enrichment for Gasoline 45
6.2 Percentage Increase in Power with Oxygen Enrichment for CNG 45
6 ..3 Increase in Exhaust Temperatures with Oxygen Enrichment 49 for Gasoline
6.4 Increase in Exhaust Temperature with Oxygen Enrichment for CNG 49
6.5 Brake Specific Fuel Consumption with Oxygen Enrichment for Gasoline 56
6.6 Brake Specific Fuel Consumption with Oxygen Enrichment For CNG 56
6.7 Percentage Reduction in CO with Oxygen Enrichment for Gasoline 65
6.8 Percentage Reduction in HC with Oxygen Enrichment for Gasoline 65
6.9 Percentage Reduction in CO with Oxygen Enrichment for CNG 66
6.10 Percentage Reduction in HC with Oxygen Enrichment for CNG 66
6.11 Power Output with 0 2 Enriched Air Supplied by Separator for Gasoline 68
Vl 6.12 Power output with 0 2 Enriched Air Supplied by Separator for CNG 68
6.13 Reduction in CO with 0 2 Enriched Air Supplied by Separator 69 for Gasoline
6.1-+ Reduction in HC with 0 2 Enriched Air Supplied by Separator for Gasoline 69
6.15 Reduction in CO with 0 2 Enriched Air Supplied by Separator for CNG 70
6.16 Reduction in HC with 0 2 Enriched Air Supplied by Separator for CNG 70
Vll LIST OF FIGURES
1.1. Summary of HC, CO, and NO Pollutant Formation Mechanism in a Spark -Ignition Engines 3
1.2. Schematic of Complete SI Engine HC Formation and Oxidation Mechanism within the Cylinder and Exhaust System 8
1.3. Schematic Drawing of a Membrane Gas Separator 12
4.1. Overall Experimental Set-up 19
4.2. Sectional View of an Injector 23
4.3. Fuel Injection and Control Mechanism For Gasoline 24
4.4. Fuel Injection and Control Mechanism for CNG 25
4.5. Sectional View of the Typical Water Dynamometer 28
4.6. The General Construction of Laminar Flowmeter 29
4.7. A Cross-Section Drawing of an Oxygen Sensor 31
5.1. Calibration Curve for Water Dynamometer 34
5.2. Calibration Curve For an Air Flowmeter 35
5.3. Calibration Curve for GM Map Sensor 36
5.4. Calibration Curve for Honda Gasoline Injector 37
5.5. Calibration Curve for Servojet Injector 38
6.1. Engine Speed versus Power Output for Gasoline 41
6.2. Engine Speed versus Power Output for CNG 44
6.3. Engine Speed versus Exhaust Temperature For Gasoline 47
6.4. Engine Speed versus Exhaust Temperature For CNG 48
Vlll 6.5. Engine Speed versus Fuel Consumption In Lb/hr for Gasoline 50
6.6. Engine Speed versus Fuel Consumption In Lb/hr for CNG 51
6.7. Engine Speed versus BSFC for Gasoline 52
6.8. Engine Speed versus BSFC for CNG 53
6.9. Engine Speed versus Thermal Conversion Efficiency for Gasoline 54
6.10. Engine Speed versus Thermal Conversion Efficiency for CNG 55
6.11. Engine Speed versus Volumetric Efficiency for Gasoline 58
6.12. Engine Speed versus Volumetric Efficiency for CNG 59
6.13. Engine Speed versus Percentage of CO for Gasoline 61
6.14. Engine Speed versus Percentage of CO for CNG 62
6.15. Engine Speed versus Percentage of HC for Gasoline 63
6.16. Engine Speed versus Percentage of HC for CNG 64
IX CHAPTER I
INTRODUCTION
The Future of the Automobile
The future of the automobile, which accounts for over half of all energy[1] used for transportation in developed countries, is of great concern since automobiles generate a significant amount of the emissions that contribute to air pollution. During the last ten years significant changes have occurred in automobile design due to energy and air pollution concerns. The result of these changes has been a move to lighter, cleaner fuel burning cars with improved aerodynamics, and smaller and more fuel efficient engines that provide higher specific output. Studies continue to be aimed at improving engine efficiencies and decreasing vehicle emissions.
The principal vehicle exhaust gas pollutants are hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), which contribute to the formation of smog as well as to acid rain. Although auto tailpipe emissions have decreased by approximately 95% in CO and HC, and 60-70% in NOx since 1970, total vehicle emissions have increased because of an increase in the number of vehicles on the road and, the number of miles driven. The future of the automotive industry depends heavily on the satisfactory reduction of exhaust emissions. Table 1.1 [2] gives the total percentage of annual US emissions from transportation and highway vehicles.
1 Table 1.1 Total Annual U.S. Emissions from Artificial Sources [2]
co HC SOx NOx Particulates
Total. Terra grams/yr 85.4 21.8 23.7 20.7 7.8
All Transportation,% 81 36 3.8 44 18
Highway Vehicles, o/c 72 29 1.7 32 14
Table 1.2 Total Exhaust Emissions per kg Fuel Burned in S.I. Engine [3]
PPM/% GMS./KG-FUEL
Hydrocarbon 300-500 PPM 25
Carbon monoxide 1%-2% 200
Oxides of Nitrogen 500-1000 PPM 25
2 CO present at high temperature and if fuel · h
Oil layers A arne source of absor C HC if combustion incomplete
(a) Compression (b) Combustion
As burned gases cool, flrst NO chemistry, then CO chemistry freezes
wall into bulk gas
tflow of HC from Piston crevices; scrapes some HC HC off burns walls (c) Expansion (d) Exhaust
Figure 1.1 Summary of HC, CO, and NO Pollutant Formation Mechanisms in a Spark-Ignition Engine.
3 Factors Influencing the Formation of Exhaust Emissions
The most important variable in determining emissions in spark-ignition engines
IS the fuel/air equivalence ratio. The ratio of the actual fuel/air ratio to the stoichiometric fuel/air ratio is defined as the fuel/air equivalence ratio. NOx, HC, and
CO formation vary strongly with equivalence ratio. The spark-ignition engine has normally been operated close to stoichiometric conditions, or slightly fuel rich, to ensure smooth and reliable engine performance. At partial load conditions, a lean mixture can be used to produce lower HC and CO, but engine performance deteriorates and eventually misfire will occur. Table 1.2 gives the typical amounts of emissions produced by spark ignition engines.
The principal source of NOx is the oxidation of atmospheric nitrogen. The
NOx level also depends on the burned gas fraction of the in-cylinder unburned gas mixture. and spark timing. The burned gas fraction depends on the amount of diluent including recycled exhaust gas (EGR) used for NOx emission control, as well as the residual gas fraction. Fuel properties will affect the burned gas condition; however, the effect of normal variation in gasoline properties on NOx production is modest.
Changes in the time history of the temperature and oxygen concentration in the burned gas as well as in the engine intake also affect the formation of NOx. Figure
1.1 shows the NOx formation mechanism.
4 Hydrocarbon emissions result from three sources: ( 1) flame quenching at the cylinder wall, (2) incomplete combustion of the hydrocarbon fuel, and (3) exhaust scavenging. Substantial amounts of hydrocarbons are also released to the atmosphere due to fuel evaporation. The hydrocarbon evaporative emissions from a vehicle arise from two sources: distillation of the fuel in the carburetor float bowl and evaporation of fuel in the gas tank.
During engine operation, the fuel vapors generated are vented internally into the intake system. During hot soak, vapors continue to be generated and are vented into the carburetor air hom. A significant portion of these vapors fmd their way to the atmosphere through the air cleaner snout. Also, whenever the carburetor fuel temperature rises up to 160° F, approximately 25-30% by volume of the fuel will evaporate [4].
Flame quenching is the principal source of unburned hydrocarbons in the exhaust of four stroke gasoline engines under normal operating conditions. As the combustion process sweeps across the chamber, each element of the cylinder wall is intercepted by the flame at a different pressure and temperature. In general, the mass of unburned hydrocarbons will be different in amount and composition at each point of the combustion chamber. Moreover, depending on whether an element of wall area is intercepted early in the cycle, right after ignition, or late in the cycle, the quenched gases have a greater or lesser time to diffuse into the bulk of hot products of combustion and undergo some degree of after-reaction there. The quenching phenomenon precludes flame propagation into small crevices such as the space
5 between the uppermost piston ring and the top of the piston, the region around the spark plug ceramic, and crevices left by imperfectly fitted head gaskets. This unburned fuel in these crevices will be swept by the piston during the exhaust stroke and will contribute to exhaust emissions level.
Incomplete combustion is the second major cause of hydrocarbon formation.
Under engine operating conditions where mixtures are extremely rich or lean, or where exhaust gas dilution is excessive, incomplete flame propagation may occur in some cycle. During transient engine operation, especially during warm-up and deceleration, it is possible that mixtures which are too rich or too lean to burn completely may fmd their way into the cylinder. When incomplete flame propagation occurs, the resulting hydrocarbon emissions will be very high.
Factors which promote incomplete flame propagation and misfires include:
1. Poor condition of the ignition system,
2. Low charge temperature,
3. Gaseous air/fuel ratio in the cylinder at and postignition,
is too rich or too lean,
4. Poor charge homogeneity, and
5. Large exhaust residual quantity.
In two-stroke gasoline engines, a third source of hydrocarbon emission comes from scavenging the cylinder with the air/fuel mixture, part of which blows through the cylinder directly into the exhaust and escapes the combustion process completely.
Hydrocarbon emissions from this type of engine may be several times larger than
6 those from naturally aspirated 4-stroke engmes. Supercharged 4-stroke gasoline
engines may have some hydrocarbon emissions from this source also.
Total hydrocarbon emission level is a useful measure of combustion
inefficiency. but it is not necessarily a significant index of pollutant emission. Table
1.3 [5] shows the average hydrocarbon composition of spark-ignition engine exhaust.
The presence of oxygen influences the oxidation of HC; the higher the percentage of
oxygen the better the oxidation. Figure 1.2 [5] shows the HC formation and oxidation
mechanism within the cylinder and exhaust system.
Carbon monoxide is an intermediate product of the combustion of hydrocarbon
fuels. Hence incomplete oxidation results in an increase in CO. When the mixture
is richer than chemically correct, substantial amounts of CO appear in the exhaust.
It is found that a change of only a small change in equivalence ratio leads to change
upto 1% in exhaust C0[4]. Figure 1.1 shows the mechanism of CO formation.
The Importance of Oxygen Enrichment
It is very important that the contribution of vehicle exhaust emissions to the
atmosphere be reduced. There are three possible ways of doing this: ( 1) by reducing
gasoline consumption (2) by using of alternate fuels such as methanol, ethanoL natural
gas, or LPG, and (3) by enriching the intake air with oxygen.
It would be difficult to reduce or eliminate gasoline consumption because of its advantages over alternate fuels, such as simplicity in handling, storing.and ease of transportation. Other problems associated with the use of alternate fuel rather than
7 Unburned HC sources: Crevices Wall phenomena Bulk quench
Oxidation products Post-combustion in-cylinder mixing
Oxidation products Exhaust port
Exhaust pipe
Figure 1.2 Schematic of Complete SI engine HC Formation and Oxidation Mechanism within the Cylinder and Exhaust System
8 Table 1.3 Hydrocarbon Composition of S.I.Engine Exhaust, Percent of Total HC
Paraffms Ole fins Acetylene Aromatics
Without Catalyst 33 27 8 32
With catalyst 57 15 2 26
9 gasoline are ( 1) some materials used in gasoline distribution systems are not compatible with alternate fuels, and (:2) present production facilities for alternate fuels cannot meet a significantly increased demand. Although the use of alternate fuels can be cost effective and generate comparatively less exhaust emissions, the problem of meeting ultra-low emissions is not solved completely.
Exhaust emissions, such as HC and CO can be reduced further by usmg enriched oxygen in the intake air of the engine. Theoretically, oxygen enrichment should have two major effects on combustion: (1) increase flame temperature, and (2) increase flame propagation velocity. These effects should increase power output, reduce the formation of HC and CO, and increase the formation of NOx. The increase in power output and reduction in HC and CO can be attributed to a higher combustion rate, whereas an increase in NOx formation is due to the combined effect of higher combustion temperature and higher oxygen fraction.
The practical viability of oxygen enrichment for internal combustion engines depends on the availability of a simple compact mechanical system driven by the engine itself. Apart from the traditional cryogenic method of extracting oxygen, there are three different methods for non-cryogenic separation of oxygen from atmospheric arr:
1. Membrane diffusion,
2. Molecular sieves, and
3. Oxygen absorption techniques.
10 Figure 1.3 [6] shows the principle of operation of a membrane polymeric gas separator. One example of this consists of minute hollow fiber tubes made up in bundles and encapsulated in a high pressure steel shell. The bundles contain thousands of fiber tubes which are sealed at one end and encased in an epoxy tube sheet at the other. Recent developments in membrane separation technology have enabled to the development of more sophisticated membrane gas separator designs that result in high performance efficiencies. The feed stream (air) flows either through the inside or outside of the hollow fibers at some suitable pressure Ph. The
opposite side of the fiber is maintained at some lower pressure, P1• A fraction of the feed, known as the "stage cut", is allowed to permeate through the membrane to the low pressure side. The feed stream is thereby separated into two streams: (a) an oxygen enriched air stream, and (b) an unpermeated (nitrogen enriched air) stream.
The magnitude of the stage cut will depend on the feed flow rate. the membrane area,
and the pressure ratio r=PJP1•
Such a membrane gas separator is considered to be a potential system for supplying oxygen enriched air for internal combustion engines because of the simplicity of the separation as well as being energy-efficient. In essence the required process equipment is simple, compact, and relatively easy to operate and control.
11 Non-permeate ~+----gas outlet (Nitrogen Enriched Air)
Fiber bundle plug
Hollow fiber ~lt-t+-+tMt-....;m~em brane
Feed stream of mixed
Permeate gas outlet (Oxygen Enriched Air)
Figure 1.3 Schematic Drawing of a Membrane Gas Separator.
12 CHAPTER II
LITERATURE SURVEY
Several projects have been initiated in the last forty-five years by a number of automobile companies and educational institutions to study the effect of oxygen enrichment for automotive applications. Both liquid fuels (gasoline and diesel) and gaseous fuels (natural gas) have been studied, but on a very limited scale. These projects include those initiated by the aviation industry using oxygen for power boosting during the second world war.
Karim and Ward [7] studied the effect of the partial pressure of oxygen in the intake charge of D.I. diesel engines. Reductions in smoke and ignition delay were observed by enriching the intake air of the engine with up to 50% oxygen. The cylinder pressure was observed to increase with oxygen concentration, while the rate of pressure rise reaching a maximum at about 38% oxygen and tended to level out at much higher concentrations.
Kodata et al. [8] investigated the formation of a fuel droplet in a high pressure gaseous environment simulating the condition existing in the cylinder of a diesel engme. The results showed that the mass of soot formed varied with oxygen concentration in the gaseous mixture.
13 It was observed that there was no soot formed at oxygen concentrations lower
than about 6CJc in N 2-02 mixtures and from this point increasing the oxygen
concentration caused the soot to increase to a maximum value. The oxygen
concentration at the maximum value was about 17(;(. After passing the maximum
value, soot decreases with further increases in the oxygen concentration.
Tsunemoto and Ishitani [9] studied the effect of intake dilution with EGR in
DI and turbocharged diesel engines. Their results indicated that decreasing oxygen
concentration with EGR led to a reduction of NOx and BMEP and to an increase in
smoke.
Plee et al. [10] carried out experiments involving both enrichment and dilution
of the charge in DI diesel engines operating at different loads and speeds. Smoke and
CO were found to increase with N 2 addition and decrease with 0 2 addition, whereas
NOx exhibited opposite trends.
Yu and Shahed [11] investigated the effect of intake charge oxygen
concentration using different diluents (EGR, C02 and N2 ). Their results showed that
dilution is effective in reducing NOx emissions at the expense of increasing smoke.
Carbon dioxide proved to be most effective in reducing NOx emissions, followed by
EGR and nitrogen, respectively.
Research carried out by Quader and \Vartinbee [12] at the General Motors
Research Laboratories revealed that adding oxygen to the intake up to 32% by volume
increased NOx emissions, decreased HC and CO emissions, decreased volumetric efficiency, decreased combustion duration, and permitted leaner engine operation. A
14 specially modified single-cylinder CFR engine and exhaust analysis apparatus were used in their study. Oxygen from a high pressure cylinder was added to the intake air in a surge tank located ahead of the intake valve. Commercially available 99.5% pure oxygen was used.
Similarly, several research projects have been conducted using natural gas as fuel. B. Detancq and J. Williams [13] have studied the effect of oxygen enrichment in the intake of an engine fueled by natural gas at Ecole Polytechnic de Montreal. A single-cylinder Ricardo E6.T engine was used for this study. An electric dynamometer was used for torque measurement. Oxygen and natural gas were supplied to the engine from a high pressure cylinder and the local utilities pipeline respectively. The mixing box for oxygen and air fed a homogeneous mixture to the natural gas carburetion unit. Natural gas at 15 psig was expanded through two pressure regulators down to ambient pressure upstream of the mixing unit. The results indicated that oxygen enrichment could be used to increase the power output of SI engines fueled by natural gas to levels equal to, or higher to the output achieved by air/gasoline mixture.
15 CHAPTER III
OBJECTIVES
Project Objectives
The overall objective of this research was to determine the performance and emissions of internal combustion engines fueled by gasoline and natural gas when operating at various levels of oxygen enriched intake air. The effect of oxygen enriched operation on gaseous emissions such as carbon monoxide and hydrocarbons was of particular interest as well as perlormance increases that offset the loss due to the introduction of natural gas in intake manifold.
Thesis Objectives
The objectives of this thesis are:
1. to build the required experimental setup. make the necessary engme modifications, and investigate the advantages and disadvantages of oxygen enriched air on the perlormance of I. C. engines; and
2. to examine the feasibility of gas separator to supply oxygen-enriched air for vehicle applications.
16 CHAPTER IV
TEST EQUIPMENT
General Plan
In the early stages of the project planning, the following equipment was identified as being required to set up the experiment:
1. A test engine that was a good representation of present day internal combustion engine technology that could be used conveniently for the test with minimum modification;
2. A dynamometer to measure the torque developed by the engine;
3. An efficient exhaust gas analyzer to measure the exhaust em1sswns; accurately;
4. Injectors to inject gasoline and compressed natural gas;
5. An electronic control mechanism to control the timing and duration of the fuel injection;
6. A fuel system to store and to transfer gasoline (25 - 30 psi) and natural gas
(60 - 150 psi);
7. An efficient data acquisition system to record all important experimental data;
8. An oxygen sensor and feed back system to maintain a correct air/fuel ratio:
9. An engine cooling system;
10. A flow meter to measure the air flowrate to the engine; and
17 11. A Hall effect sensor (magnetic pickup) to monitor exhaust valve closing to time the fuel injection.
The engine had to be modified to accommodate the fuel injector, the Hall effect device, thermocouples (K-type), and pressure sensors to measure the inlet and manifold pressures.
The complete experimental setup used is shown in Figure 4.1. To reduce complexity and modification time, it was decided that a single-cylinder engine would be used. A four-stroke, two-valve, air cooled, spark ignition, 250cc, Honda engine, which was available in the engine laboratory, was used in this research. A list of general specifications for this engine are given in Table 3.1.
Modified Test Engine
The engine was modified to inject the fuel as close as possible to the engine inlet port. Originally, this engine was carbureted. The carburetor was removed, and a new manifold system was fabricated. An adapter was fabricated and attached to the intake manifold using a J.B. weld. A hole was drilled in the adapter at a 45 degree angle and the injector was installed in this hole to inject the fuel close to the engine inlet port. A butterfly valve was installed in the manifold upstream of the injector.
Fuel injected at the time of exhaust valve closing. A hole was drilled in the exhaust side of the engine head and a magnetic pickup (Hall effect sensor) was installed just above the exhaust valve. A magnetic strip was placed on the top of the exhaust valve stem to allow the magnetic pickup to sense the closing of the exhaust valve.
18 N2 Cylinder Exhaust Analyzer
Oxy. Enriched Air ,_. \.0 Compressed Three way Air Tank :4-- Valve From 1. Load Cell Compressor 2. water Inlet Data Aquisition 3. Drive Shaft Board 4. Flexible Couple 5. Water Outlet 6. Inlet Temp. Sensor 7. Inlet Pressure Senor Display 8. Outlet Pressure Test Engine Monitor Sensor Feed Back 9. Ex. Temp. Sensor System 10. Oxy. Sensor 11. Exhaust System
Fig 4.1 Overall Experimental Sd- up Table 3.1 Test Engine Specification
Type : 4-Stroke, DOHC, 2-Valve, !-Cylinder
Cooling System :Air Cooled
Bore and Stroke : 74mm By 57.3mm
Displacement Volume : 246 cc
Compression Ratio : 9:1
Fuel System : Modified for fuel Injection
Lubrication : Forced pressure, wet sump, SAE 1OW -40
Valve Timing
Inlet : Open 8° BTDC
: Close 35° ABDC
Exhaust : Open 50° BTDC
: Close 40° ATDC
20 Measurement of exhaust temperature, emissions, and oxygen in the exhaust was necessary. The measurement of the oxygen level in the exhaust was necessary to maintain an accurate air/fuel ratio. A thermocouple was placed in the exhaust duct close to the exhaust port. An oxygen sensor and gas analyzer probes were placed in the exhaust duct downstream of the thermocouple. The tip of the gas analyzer probe was positioned to face the exhaust emissions flow.
The air flow rate into the engine was measured to calculate volumetric efficiencv. Inlet pressure. manifold pressure, and inlet temperature were also recorded. A Meriam air flow meter was installed at the inlet of the engine to measure the air flowrate. GM MAP (Manifold Absolute Pressure) sensors were placed at the inlet and outlet of the air flow meter to record the inlet and intake manifold pressures, respectively. A hole was drilled at the inlet of the air flow meter and a temperature sensor was installed to measure inlet temperature.
A cradle was fabricated to mount the Honda test engine and bolting it to the test stand. For all tests, the starter motor provided on the test stand was used for cranking with power supplied by a battery. The wiring circuits were completed to make the ignition and starting systems fully functional. A personnel protection system was built around the engine to ensure the safety of the staff involved in the test.
21 Fuel Injection System
A steel tank with adequate capacity to provide enough gasoline to run the engine at wide open throttle for the duration of the test. Stainless steel 1/4 inch tubing was used to supply the fuel to the injector. A nitrogen cylinder was used to pressurize the fuel tank to 25 psi and this pressure was maintained throughout the experiment by a pressure regulator. It was necessary to pressurize the fuel tank to get the proper atomization of the fuel to have a uniform air/fuel mixture.
The Injector
A Honda and servojet electronic injectors were used for injection of gasoline and compressed natural gas, respectively. The gasoline injector was mounted on the manifold at an angle of 45 degrees and close to the inlet of the engine. The reason for using fuel injection in lieu of the carburetor suggested in the engine was to provide the necessary control over fuel metering. A sectional view of the injector is shown in Figure 4.2. [5]
Injector Control Mechanism
In order to control the timing and duration of the fuel injection, an injector control mechanism was used. Figures 4.3 and 4.4 show schematic diagrams of the injector control mechanism for gasoline and natural gas, respectively. An injector controller supplied by Moog Controls, Inc., was used to switch the injector on and off and to control the duration of injection. This Moog controller provided adjustments
22 Winding Return Spring
Valve Needle
Pintle
Figure -+.~ Sectional View of an Injector
23 Magnetic Sensor
Power Supply
• I Osciloscope Oxygen Sensor ~
feedback System
Figure 4.3 Fuel Injection and Control Mechanism for Gasoline Power Supply
Controller
Gas Flow
N l..ll Power Supply
Feed back System Osciloscop
Figure 4.4 Fuel Injection and Control Mechanism for CNG for "injection delay" and "injection width." The injection delay is the time period after receiving a pulse by the controller and the moment when the controller triggers the injector open. Injection width is the time the injector remains open (pulse width).
A Hall effect sensor (magnetic pickup) was used to sense the closing of the exhaust valve during operation of the engine. This sensor was coupled with the injector control mechanism so that the fuel injection could be timed to coincide with opening of the inlet valve. To ensure correct injection timing, a small magnet was placed at the tip of the exhaust valve stem. The magnetic sensor (Hall effect sensor) was positioned close to the exhaust valve so that the sensor picked up a magnetic pulse every time the magnet came in contact with it. This sensor was connected to the Moog controller, which in tum controlled the injector.
For every closing of the exhaust valve (40° ATDC), the Hall effect sensor signalled the Moog controller. Upon receiving the signal from the Hall effect sensor, the Moog controller triggered the injector open and fuel was injected. The duration of the injection was controlled by adjusting the pulse width knob provided on the
Moog controller.
Water Dynamometer
A model D-1 01 water dynamometer was used to measure the torque output of the engine. This dynamometer consists of a rotor and a stator, both encased in single housing. The housing is filled with water to load the engine. The dynamometer blades resist fluid flow through the rotor based on the level of water in the housing.
26 The stator also acts as the brake housing. The water inlet was controlled by a gate valve which was used to control the amount of water for power absorption. The rotor was flanged to the drive shaft of the engine and is free to turn within the stator. The torque was measured by means of strain-gage elements (load cell) which were bonded to the transmission shaft. Figure 4.5 shows a cut-away of a typical water dynamometer.
Air Flowmeter
A Meriam laminar flowmeter, Model 50MC2, was used to measure the inlet air flow rate. This flow meter was coupled directly to the inlet manifold of the test engine by means of a short piece of hose. The differential pressure across the laminar flowmeter was measured by using two GM MAP pressure sensors which were located at the inlet and outlet of the flowmeter, respectively. Figure 4.6 [14] shows the general construction of laminar flowmeter.
Mass Flowmeter for Natural gas
A MKS, Type 558A, mass flowmeter was used to measure natural gas consumption by the engine. The MKS flow meter is a laminar flow device whose precise indication of mass flow is achieved through the use of a range-controlling, changeable bypass and paralleling sensor tube. Upon entering the flowmeter, the gas stream is divided into two parallel paths: the first is directed through the sensor tube and the second through the changeable bypass. The two paths rejoin to pass through
27 Impeller rotor
Water fill
Input shaft
Torque arm-
Torque measurement Water empty
Figure 4.5 Sectional View of the Typical Water Dynamometer
28 CONNEC TlON S
'----FLOW '---FLOW STRAIGHTENER STRAIGHTENER METERING SECTION
Figure 4.6 The General Construction of Laminar Flow Meter
29 the control valve before exiting the instrument. In this mass flowmeter, resistance heaters are wound on the sensor tube and form the active legs of bridge circuits.
Their temperatures are established such that a voltage change on the sensor winding is a linear function of a flow change. This signal is then amplified to provide 0-5
VDC output. This output voltage is calibrated to the flow rate of the natural gas.
Oxygen Sensor
The engme operating fuel/air ratio was maintained close to stoichiometric through the use of an oxygen sensor in the exhaust system. The oxygen sensor was located in the exhaust manifold close to the exhaust outlet. This location provided for rapid warm-up of the sensor, and also gave the shortest signal delay time from the fuel injector to the feedback system. The sensor provided a voltage depending upon the concentration of oxygen in the exhaust gas stream. This signal was fed to an indicator and the fuel/air ratio was controlled manually to stoichiometric. Figure 4.7 cross-section drawing of an oxygen sensor [5].
30 Posttt~ electncal tennmal Insulator
Shell ( ncgat•~ electrical tenn1naJ)
Graphite seal and contact
Sensor Body
EJNnst manifold
Figure 4.7 A Cross-Section Drawing of an Oxygen Sensor
31 Exhaust Gas Analyzer
The Horiba Mexa-Ge automotive emission analyzer was used to measure the levels of CO and HC in the exhaust of the test engine. A cylindrical tube, l/2 inch in diameter was welded to the exhaust manifold to hold the measuring probe. The cylindrical tube was positioned in such way that the probe could be inserted into the middle of the exhaust gas stream. This was necessary for accurate measurement. CO and HC emissions were recorded in terms of percentage and PPM, respectively, from the digital display of the analyzer.
Data Acquisition System
Rapid data acquisition was necessary to record the test results. To accomplish this an IBM XT with two Metrabyte data acquisition boards was used. All the thermocouples. pressure sensors, and strain gage elements (load cell) were connected to the data acquisition board.
32 CHAPTER V
TEST PROCEDURE
The following topics outline the plan of experiments conducted to study the performance of an I.C. engine with enriched oxygen at different levels in the intake of the engine fueled by both gasoline and compressed natural gas.
Calibration
Everv measurmg svstem must be provable. It must be able to measure reliabh·. The procedure for this is called calibration [15]. It consists of determining the system's scale. At some point during the preparation of the system for measurement, known magnitudes of the basic input quantities must be fed to the detector transducer and the system's behavior observed.
The input may be static or dynamic. depending on the application; however, quite often dynamic response is based on static calibration, simply because a known dynamic source is not available. Figures 5.1 through 5.5 depict the calibration graphs for the water dynamometer, the Meriam linear flow meter, the GM MAP sensors, the
Honda gasoline injector, and the servojet compressed natural gas injector, respectively.
33 50
40
.:::: I .D 30 a) ::s 8" 0 E- 20
10
0 ~----~----~----~----~----~--~~--~~--~ 0 2 4 6 8 Output, volts
Figure 5.1. Calibration Curve for Water Dynamometer
34 18
16
14
12
~ u 10 £ ~ ""' ~ 8 0 ...... u.. 6
4
2
0 0 2 3 4 5 6 7 8 9 Pressue drop, inches of water
Figure 5.2. Calibration Curve for Air Aowmeter
35 25
Ol) l: <.o.... 0 20 Vl ..c~ u ·-c e 15 Vl=' eVl 0. B =' 10 0 -Vl .0< 5
0 ~--_. ____~ ___. ____ ~ ___. ____ ~--~----~--~--~ 0 2 3 4 5 Output, Volts
Figure 5.3 Calibration Curve for GM Map Sensor
36 .s E 80 0 u £ CIS """ ~ 60 u:0
40
pulse width, msecs. Figure 5.4. Calibration Curve for Honda Gasoline Injector
37 40 r---~~---.----~----~----~----~----~----~ Ill 120, psig
35 • 70, psig
30
25 '2 ~ E ...... 20 '- ~ :.::l 11) 0 15
10
5
0------L-----~----~----~--~~--~----~----~ 0 5 10 1 5 20
Pulse Width, msecs.
Figure 5.5 Calibration Curve for Servojet Injector
38 Preliminary Tests
To ensure the correct performance of the system and the normal function of the test engine, it was initially operated for a few hours using both gasoline and compressed natural gas with normal air. During this initial run, the performance of the system was carefully observed. Malfunctioning of components and leakage in air, water, and fuel lines were corrected before the actual tests were initiated. Table 5.1 shows the conditions during the evaluation of the tests.
During the preliminary tests at wide open throttle, the following parameters were monitored at various speeds :
1. the power output,
2. torque output,
3. fuel consumption,
4. inlet and exhaust temperatures, and
5. exhaust emissions
Variable speeds were obtained by loading the engine with the water flow rate in the dynamometer.
Gasoline Tests
The outlet pressure of the low pressure regulators from compressed air tank and oxygen enriched cylinder were maintained at 5 inches of water. At this pressure the air flow rate was sufficient to run the engine at wide open throttle. The pressure in the gasoline tank was maintained at 25 psi. The engine was cranked using the
39 Table 5.1 Test Conditions
Engine Speed Variable
Throttle Position Wide Open
Ignition Timing 31°
Air Inlet Temperature 22° c
Air Inlet Pressure (Gage) 5 Inches of Water
Atmospheric Pressure 690 mm of Hg
40 starter motor provided on the engine stand powered by a battery. The tests were carried out at wide open throttle at various speeds by adjusting the load on the engine. The measured data such as power output, torque, and speed were compared with analytically calculated results. The fuel consumption and exhaust emissions were compared with standard data available for S.I. engines fueled by gasoline. The tests were repeated several times under similar conditions and the repeatability was found to be within 5 percent.
Compressed Natural Gas Tests
The gasoline injector was replaced by a servojet injector which was specially designed for natural gas injection. By trail and error, the CNG inlet pressure to the injector required to crank the engine was found to be approximately 10 psi, and the pressure required to run the engine at a wide open throttle varied from 40-7 5 psi. The measured data agreed with analytically calculated results and available standard data.
The repeatability was again found to be within 5 percent.
41 CHAPTER VI
TEST RESULTS
In this chapter, the results of experiments conducted to study the effect of
oxygen enrichment on the performance and emissions of internal combustion engines
fueled by gasoline and natural gas are presented. After studying and evaluating the
performance and emissions of the engine with normal air (21% Oxygen), of
experiments were conducted to assess the effects of oxygen enrichment in the intake.
The oxygen concentration was varied between 23% and 25%. All the data were
obtained at the wide open throttle position at various engine speeds. The analysis of
results obtained revealed that the engine performance was improved and significant
reductions in exhaust emissions such as CO and HC were observed with oxygen
enrichment in the intake.
Brake-Horsepower
Figures 6.1 and 6.2 show the effect of oxygen enrichment on the power output
of the engine at different levels of oxygen in the intake air fueled by gasoline and
natural gas, respectively. It can be seen that the power output increased with
increased percentage of oxygen. Tables 6.1 and 6.2 give the percentage increase in the power output for gasoline and natural gas, respectively. An increase in power output of 5%-17% for oxygen enriched air/gasoline mixtures and 2%-16% for oxygen enriched air/natural gas mixtures was observed. It is also noticed that power output
42 •
6200 6400 6600 6800 Engine Speed (RPM)
Figure 6.1 Engine Speed versus Power Output for Gasoline
43 Normal Air • 23%0xy. 17 • 25% Oxy. •
16
15 0. :I: .J' ::I 0. 14 ~ ::I 0 ~ a) ~ 13 0 0.. 12
11
10 ----~--~------~--~~--._--~--~------~ 5600 5800 6000 6200 6400 6600 Engine Speed (RPM) Figure 6.2 Engine Speed versus Power Output for CNG
44 Table 6.1 Percentage Increase in Power with Oxygen Enrichment for Gasoline
Speed BHP with BHP with Percent BHP with Percent Rpm Normal Air 23%02 air Increase 25% 0 2 Air Increase
6200 15.229 16.507 8.39 17.782 16.76
6350 16.53 17.50 5.87 19.032 15.13
6500 17.65 19.08 8.10 20.05 13.59
6700 16.0 16.8 5.0 17.58 9.88
Table 6.2 Percentage Increase in Power with Oxygen Enrichment for CNG
Speed BHP with BHP with Percent BHP with Percent Rpm Normal Air 23%02 air Increase 25% 0 2 Air Increase
5700 12.56 13.4 6.68 14.2 13.06
5900 14.08 15.2 7.95 16.34 16.05
6100 15.8 16.54 4.68 17.4 10.13
6350 13.8 14.2 2.89 14.7 6.52
45 with '25% oxygen enriched air/natural gas mixtures equal to power output with air/gasoline mixtures. The increase in power output can he attributed to improvement in fuel combustion.
Exhaust Temperature
Figures 6.3 and 6.4 illustrate the increase in exhaust temperatures for gasoline and natural gas with different levels of oxygen content. The exhaust temperatures were higher due to improved combustion, when excess oxygen was present.
Tables 6.3 and 6.4 show the increase in exhaust temperatures for gasoline and natural gas, respectively. It was noted that the overall increase in temperature with increased in oxygen content is more with gaseous fuel as compare to liquid fuel. It was prabably due to the fuel intake into the cylinder being higher when operating with gasoline. The liquid fuels would provide more cooling effect due to higher evaporation as compare to gaseous fuels.
Brake Specific Fuel Consumption and Fuel Conversion Efficiency
It was observed that fuel consumption was increased with oxygen enrichment.
This is due to higher exhaust temperature and higher energy losses to the cooling systems. In this case, the air blower was used as a cooling system. Figures 6.5 and
6.6 show the fuel flowrate at different speeds for gasoline and natural gas, respectively. Tables 6.5 and 6.6 give the brake specific fuel consumption.
46 900 Normal Air • 23%0xy. • 25% Ox . 880 • 0 "0 ~ ~ .....00 860 ·-c u0 00 0 0 840
.....~ ~ ~ 0 820 s0.. ~..... c:l.)::s 800 .c~ >< ~ 780
760 6000 6200 6400 6600 6800 Engine Speed, Rpm
Figure 6.3 Engine Speed versus Exhaust Temperature For Gasoline
47 900 • d) "'0 ~ 1-o 850 ·;:0.0 c: ud) ~ 0.0 d) 0 ~ ~ 800 .....:l ~ 1-o d) 0. E ~..... V) :l ~ 750 ..c: >< U.l
700~--~--~--~---L--_.--~------~~----~ 5600 5800 6000 6200 6400 6600 Engine Speed (RPM)
Figure 6.4 Engine Speed versus Exhaust Temperature For CNG
48 Table 6.3 Increase in Exhaust Temperature with Oxygen Enrichment for Gasoline
Speed Exhaust Temperature (deg.cent.) Rpm Normal Air 23% 0 2 Air 25% 0 2 Air
6200 799 830 833
6350 820 842 845
6500 835 850 858
6700 848 862 889
Table 6.4 Increase in Exhaust Temperature with Oxygen Enrichment for CNG
Speed Exhaust Temperature (deg.cent.)
Rpm Normal Air 23% 0 2 Air 25% 0 2 Air
5700 735 808 820
5900 755 816 830
6100 760 830 852
6350 778 848 864
49 Normal Air • 23%0xy. • 25%0xy.
8.5
--~ ~ ~ ....J...._, 8.0 ~ ~ ~ ~ 0 -~ 0) -::s ~ 7.5
6200 6400 6600 6800 Engine Speed (RPM)
Figure 6.5 Engine Speed versus Fuel Consumption In Lb/hr for Gasoline
50 Nocma!Air 23% Oxy. 5.7 25% Oxy.
5.5 ,-... ~
...... X ~ 5.3 .J --...~ e 5.1 ~ 0 -u.. -~ 4.9 u..::s
4.7
4.5 5 6 0 0 5 8 0 0 6 0 0 0 6 2 0 0 6 4 0 0 6 6 0 0 Engine Speed (RPM)
Figure 6.6 Engine Speed versus Fuel Consumption In Lb/hr for CNG
51 0.50 Normal Air 23% Oxy. 0.49 •• 25% Oxy. 0.48
...- 0.47 ~ :I: I 0.. 0.46 ~ ~ ..J..._, u 0.45 en~ ~ 0.44 0.43 • 0.42 6000 6 2 0 0 6 4 0 0 6 6 0 0 6 8 0 0 Engine Speed (RPM)
Figure 6.7 Engine Speed versus BSFC for Gasoline
52 Noona!Air 23%0xy. 0.42 25%0xy.
,.-._ 0.40 X "I ~ 0.38 ~ ~ ~ u 0.36 u.- Cl) ~ 0.34 0.32 • 0.30 5600 5800 6000 6200 6400 6600 Engine Speed (rpm) Figure 6.8 Engine Speed versus BSFC for CNG
53 34 .. Normal Air ,.-..._ 23% Oxy. ~ • 25% Oxy. '-' • ;;..., u 32 c: Q.) ·-u ~ tlJ c: 30 0 ·-Cl.) Q.)"" >c: 0 u 28 ~ § Q.) ~ 26
24 L___ ~ ___L __ _. __ ~~--~--~--~---- 6000 6200 6400 6600 6800 Engine Speed (RPM)
Figure 6.9 Engine Speed versus Thermal Conversion Efficiency for Gasoline
54 40 ~ Normal Air 23%0xy. • 25%0xy. 38 • --~ '-' • >. C,) c: 36 ~ s·-C,) r.I.l c: 34 0 ·-Cl) ~ ""'> c: u0 32 ca § ~ ~ 30
28 ~--~--~--~--~--~--~--~---L--~--~ 5600 5800 6000 6200 6400 6600 Engine Speed (RPM)
Figure 6.10 Engine Speed versus Thermal Conversion Efficiency for CNG
55 Table 6.5 Brake Specific Fuel Consumption with Enriched Oxygen for Gasoline
Speed Brake specific fuel consumption (Lbm/hp-hr) Rpm for Normal Air for 23% 0 2 air for 25% 0 2 Air
6200 0.483 0.463 0.457
6350 0.463 0.453 0.440
6500 0.458 0.432 0.4266
6700 0.465 0.456 0.449
Table 6.6 Brake Specific Fuel Consumption with Oxygen Enrichment for CNG
Speed Brake specific fuel consumption (Lbm/hp-hr)
Rpm for Normal Air for 23% 0 2 air for 25% 0 2 Air
5700 0.382 0.378 0.370
5900 0.368 0.359 0.344
6100 0.345 0.334 0.318
6350 0.410 0.399 0.389
56 Although the fuel flowrate increased with increased oxygen percentage, the brake specific fuel consumption (BSFC) decreased with increased oxygen emichment, which in tum gave the higher thermal conversion efficiency. This is attributed to increased combustion with increased oxygen in the intake air. Figures 6.7 through 6.10 show the plots of B SFC and fuel conversion efficiency for gasoline and natural gas.
Volumetric Efficiency
Introducing additional oxygen in the intake charge of the engine reduced the volumetric efficiency considerably. The reason is that the density of the entering air decreased due the hotter inlet port and combustion chamber walls. Theoretical calculations show that the amount of air required for combustion is decreased by 9%-
190C with oxygen emiclunent. Theoretical calculation of air requirement for complete combustion of one kg. of fuel is shown in Appendix B. A reduction in volumetric efficiency is about 9%-11% for gasoline and 1%-2% for natural gas was experienced.
Figures 6.11 and 6.12 show volumetric efficiencies for gasoline and natural gas, respectively.
57 100
Normal Air 95 • • 23% Oxy . • 25% Oxy. 90 ....-_ ...._,~ >. u 85 c ~ ·-u ~ ~ 80 UJ u ·-b ~a 75 = -~ 70
65
60 ~--_. _____. ____ ~------60')0 6200 6400 6600 6800 Engine Speed (RPM)
Figure 6.11 Engine Speed versus Volumetric Efficiency for Gasoline
58 75 Normal Air 23% Oxy. 74 • e 25%0xy. • 73 •
72 --.._..~ >. uc:: 71 0 ·u- ~ tJ.) 70 u ·c:.... 0 E 69 :l :9 68
67
5800 6000 6200 6400 6600
Engine Speed (RPM)
Figure 6.12 Engine Speed versus Volumetric Efficiency for CNG
59 Exhaust Emissions
The effect of oxygen enrichment on exhaust gas emissions is shown in Figures
6.13 through 6.1b. The drop in both CO and HC emissions with excess oxygen in the intake charge was expected. This can be attributed to the increased combustion with the higher combustion temperature and higher oxygen fraction. In the presence of
higher oxygen content, the CO oxidized to C02 and HC reacted with oxygen and burned in the latter stages of the combustion.
Tables 6.5 through 6.8 give the percentage reduction in CO and HC at 23% and 25lff of oxygen in the intake charge for both gasoline and natural gas used as fuels. The reduction in CO was approximately 24%-32% for gasoline and 16%-27% for natural gas. The reduction in HC was approximately 29%-40% for gasoline and
26o/c-38% for natural gas. The highest reduction in exhaust emissions was observed at the best performance of the engine.
Test Results with Gas Separator
An attempt was made to use the membrane gas separator to supply oxygen enriched air to the test engine. Up to 50% pure oxygen enriched air was supplied by the gas separator. This enriched air was mixed with atmospheric air to increase the percentage of oxygen in the intake charge. The fmal oxygen percentage was varied between 22% and 23%. The results obtained is shown in the Tables 6.11 through
6.16. Although the power increase is meager, the reduction in CO and HC is close
60 1.8 Normal Air 1.7 • 23% Oxy . 25% Oxy. 1.6 • ,-.., 1.5 ~ '-" c 0 1.4 ·~ ~ b c 1.3 0) u c 1.2 u0 0) "0 1.1 >< ·-0 c 1.0 0 § • 0 ~ u~
6200 6300 6400 6500 6600 6700 6800 Engine Speed (RPM)
Figure 6.13 Engine Speed versus Percentage of CO for Gasoline
61 1.3 • 1.2 25%0xy...... • ~ '-" c 1.1 0 ...... ·-~ !:I c d) u 1.0 c u0 d) '"0 0.9 ·->< 0 c 0 8 c 0.8 0 .0a u 0.7 •
5800 6000 6200 6400 6600
Engine Speed (RPM)
Figure 6.14 Engine Speed versus Percentage of CO for CNG
62 230 Normal Air 23% Oxy . • 25% Oxy. ..-. 210 • ~ ~ .._~ c 190 0 ..... ·-~ ..... """c d) u 170 c u0 c 0 150 .D ~ u 0 -i3 130 ~ :I:
110
90 6000 6200 6400 6600 6800 Engine Speed (RPM)
Figure 6.15 Engine Speed versus Percentage of HC for Gasoline
63 100 Normal Air 23% Oxy. 90 25% Ox ...... ~ 0.. ..._,0.. 80 c 0 ..... ·Cd- tl c 70 a,) u c u0 c 60 0 .0 ~ g 50 "0'""' >. ::I: 40
30 5600 5800 6000 6200 6400 6600
Engine Speed (RPM)
Figure 6.16 Engine Speed versus Percentage of HC for CNG
64 Table 6.7 Percentage Reduction in CO with Oxygen Enrichment for Gasoline
Speed CO Rpm Normal Air ::?J(7r0, air Reduction 25(7c 0 2 Air Reduction 6200 1.50 1.11 26.0 1.04 30.67 6350 1.42 1.067 24.85 0.97 31.69 6500 1.30 0.95 26.95 0.88 32.30 6700 1.35 1.012 25.05 0.95 29.62 Table 6.8 Percentage Reduction in HC with Oxygen Enrichment for Gasoline Speed HC Ppm HC Ppm Percent HCPpm Percent Rpm Normal Air 23%02 air Reduction 25% 0 2 Air Reduction 6200 190 134.50 29.21 120.00 36.84 6350 186 130.25 29.14 113.50 38.97 6500 175 124.00 30.40 105.00 40.00 6700 180 126.03 29.08 110.00 30.89 65 Table 6.9 Percentage Reduction in CO with Oxygen Enrichment for CNG Speed CO% for CO% for Percent CO % for Percent Rpm Normal Air 23%02 air Reduction 25% 0 2 Air Reduction 5700 1.078 0.905 16.05 0.83 23.005 5900 1.050 0.880 16.19 0.79 24.76 6100 0.955 0.750 21.50 0.69 27.74 6350 1.090 0.915 16.05 0.85 22.02 Table 6.10 Percentage Reduction in HC with Oxygen Enrichment for CNG Speed HC Ppm HC Ppm Percent HC Ppm Percent Rpm Normal Air 23%02 air Reduction 25% 0 2 Air Reduction 5700 75 55 26.67 50 33.33 5900 70 49 30.00 47 32.85 6100 70 46 34.30 43 38.75 6350 85 58 31.80 52 38.80 66 to reduction in CO and HC at 23o/r oxygen. This is due to variation in percentage of oxygen in the intake for every working cycle of the engine. The increase in power output due to oxygen enriched air can be utilized to run the air compressor to feed air through the gas separator at some higher pressure. The Advances in membrane separation technology permit upto 98% of the feed air to be recovered at higher oxygen content than in ambient air. Approximately 21 - 26 SCFM of air is required as feed to the membrane gas separator to obtain 20 - 25 SCFM of 23o/c oxygen enriched air. Twenty- 25 SCFM 23% of oxygen enriched air was required to run the test engine used in this research project at wide open throttle. In addition to increased in power output at 23% oxygen enriched air, additional 1 HP is needed to compress 21 - 26 SCFM of air at 50 psi. This estimation is based on approximate design parameters of an air compressor. 67 Table 6.11 Power Output with 0 2 Enriched Eir Supplied by Separator for Gasoline Speed Power Output Power Output %Increase Rpm Normal Air 0 2 Enriched Air in Power 6200 15.229 15.70 3.30 6350 16.53 17.50 5.95 6500 17.65 18.29 3.62 6700 16.00 16.51 3.18 Table 6.12 Power Output with 0 2 Enriched Air Supplied by Separator for CNG Speed Power Output Power Output %Increase Rpm Normal Air 0 2 Enriched Air in Power 5700 12.56 13.4 6.68 5900 14.08 14.67 4.19 6100 15.80 16.50 4.43 6350 13.80 14.60 5.79 68 Table 6.13 Reduction in CO with 0 2 Enriched Air Supplied by separator for Gasoline Speed Percent CO Percent CO for Percent Reduction Rpm for Normal Air 0 2 Enriched Air in co 6200 1.50 1.20 20.0 6350 1.42 1.10 22.5 6500 1.30 0.98 24.6 6700 1.35 1.02 23.61 Table 6.14 Reduction in HC with 0 2 Enriched Air Supplied by Separator for Gasoline Speed HC, Ppm HC, Ppm for Percent Reduction Rpm for Normal Air 0 2 Enriched Air in HC 6200 190 145.0 23.68 6350 186 140.0 24.63 6500 175 132.0 24.73 6700 180 137.5 23.61 69 Table 6.15 Reduction in CO with 0 2 Enriched Air Supplied by separator for CNG Speed Percent CO Percent CO for Percent Reduction Rpm for Normal Air 0 2 Enriched Air in co 5700 1.078 0.95 11.80 5900 1.05 0.90 14.30 6100 0.955 0.81 15.18 6350 1.09 0.98 10.09 Table 6.16 Reduction in HC with 0 2 Enriched Air Supplied by separator for CNG Speed HC, Ppm HC, Ppm for Percent Reduction Rpm for Normal Air 0 2 Enriched Air in HC 5700 75 65 21.28 5900 70 53 24.28 6100 70 50 28.57 6350 85 65 23.52 70 CHAPTER VII CONCLUSIONS Conclusions This research was undertaken to test the performance and emissions of a spark ignition engine fueled by both liquid and gaseous fuel using oxygen enriched air. An attempt was made to examine the practicability of using a membrane gas separator to supply oxygen enriched air. The results of oxygen enrichment experiments lead to the following conclusions: 1. An increased in engine power output. The use of natural gas in S.I. engines results m reduced volumetric efficiency due to displacement of air in the intake manifold. The results from the experiment indicate that oxygen enrichment can be used to increase the power output of an engine fueled by natural gas to levels equal to or higher than that achieved using air/gasoline mixtures. The increase in power output may also be utilized to provide the some of the benefits of a supercharger or turbocharger at higher altitudes. 2. Substantial reduction in CO and HC were achieved. This is one of the most important benefits of the oxygen enriclunent . 3. An improvement in thermal conversion efficiency. 4. Increased exhaust temperatures, reduced combustion noise, constant fuel economy, and decreased volumetric efficiency were also observed. 5. In addition to the above effects, the formation of NOx should also increase 71 with increased oxygen percentage. This is because the NOx formation is increased at higher temperatures. This could possibly be offset by increased EGR. \Vith current and future developments in the area of air separation technology and development of ceramics for automotive engines, it should be possible to use oxygen enrichment in the near future. Suggestions for Future Research In this study. the effect of oxygen enrichment was not tested for compression ignition engines. Similar tests can be conducted to test the performance of compression ignition engines as well as multi cylinder engines. It is suggested that the testing of oxygen enrichment with low grade fuels may yield useful information for possible use in automobiles. Further research can be carried out with gas separators. Depending on the success in the laboratory, the device could be installed in a vehicle and tested. 72 REFERENCES 1. Jamil Ghojel and John C. Hillard, "Effect of Oxygen Enrichment on the Performance and Emissions of l.D.I Diesel engines," Paper# 830245, Society of Automotive Engineers, 1983. "Marks Standard Hand-Book for Mechanical Engineers," McGraw-Hill Publishing Company. New York, 1992. C.F. Taylor, "The Internal Combustion Engines in Theory and Practice," Vol. II, The M.I.T. Press, Massachusetts, 1979. 4. D.J. Patterson, :1\.A. Henein, "Emissions from Combustion Engines and Their Control," Ann Arbor Science Publishers Inc. Ann Arbor, 1972. 5. John B. Heywood, "Internal-Combustion Engine Fundamentals," McGraw-Hill Publishing Company, New York, 1988. 6. Thorbjorn Johannessen, "Operational Experince with Nitrogen Generation Through Membrane Seperation," Maritime Projections, Oslo, Norway, 1986. 7. G.A. Karim and G. Ward," The examination of the Combustion Process in a C.I. Engines by Changing the Partial Pressure of Oxygen in the Intake Charge," Paper# 680767, Society of Automotive Engineers, 1968. 8. T.Kadota and H. Hiroyasu, " Soot Formation by a Combustion of a Fuel Droplet in High Pressuere Gaseous Environments," Journal of Combustion and Flame, Vol. 29, 67-75, 1977. 9. H. Tsunemoto and Hironi, " The Role of Oxygen in the Intake and Exhaust on Emissions, and Smoke and BMEP of a Diesel Engine with EGR system," Paper # 800030, Society of Automotive Engineers, 1980. 10. S.L. Plee and T. Ahmed," Efeects of Flame Temperature and Air-Fuel Mixing on Emission of Particulate Carbon from a Divided-Chamber Diesel Engine," G.M. Symposium, Michigan, 1987. 11. R.C. Yu and S.M. Shahed, " Effects of Injection Timing and Exhaust Gas Recirculation on Emissins from a D.I.Diesel Engine," Paper# 811234, Society 73 of Automotive Engineers, 1981. 12. A.A. Quader and Wartenbee, "Exhaust Emissions and Performance of a Spark Ignition Engine Using Oxygen Enriched Intake Air," Fuels and Lubricants Department, General Motors Laboratories, Warren, Michigan, 1978. 13. B. Detuncq and J. Williams, " Performance of a Spark Ignitioon Engine Fueled by Natural Gas Using Oxygen Enriched Air," International Fuels and Lubricants Meeting Exposition, Portland, Oregon, 1988. 14. " Instructional Manual for Meriam Laminar Flowmeter." 15. Edger E. Ambrosius, " Mechanical Measurement and Instrumentation," McGraw-Hill Book Publishing Company, New York, 1963. 74 APPENDIX A: BASIC COMPUTATIONS The following set of equations were used to calculate the ensuing parameters. 1. Volumetric Efficiency ------eq. (·-l.l) Va = Volume of air inducted into the cylinder in CFM V d = Rate at which volume is displaced by the engine piston d = Diameter of the bore 1 = stroke length !\ = speed in rpm 2. Fuel flow rate of CNG Flow rate = V ou/Vmax *R *CGP l/m ------eq. (4.2) V out = Output voltage of the flowmeter V max =Maximum voltaaeo corresponds to maximum flow rate (5 V) R = Max flow rate of the flowmeter 400 SLM GCF = Gas correction factor for methane 0.72 75 3. Specific Fuel Consumption SFC = ~/P lbm/hp-hr ------eq.(4.3) Mf = Mass of Fuel Lbm/Hr P = Power developed in Hp -+. Fuel Conversion Efficiency 11t = 2545/SFC * QHv ------eq. (4.4) SFC = Specific Fuel Consumption in Lbm/Hr-Hp QH\. = Heating Value of Fuel in Btu/Lbm 76 APPENDIX B: THEORETICAL AIR CALCULATION The following calculations show the theoretical air requirement for complete combustion of one kg. of fuel with different levels of oxygen in the air. Gasoline (a). Normal Air C8H 18 + 0 2 + N 2 = C02 + H20 + N2 For one mole of 02, 79/21 = 3.762 moles of N2 1s involved. Hence the balancing the above equation yields C8H18 + 12.502 +47N2 =8C02 + 9H20 + 47N2 Theoretical Air/Fuel= (12.5+47) * 28.97/114 = 15.12 kg/kg. of fuel (b). 23o/c oxygen C8H 18 + 12.502 +41.87N2 =8C02 + 9H20 + 41.87N2 Theoretical Air/fuel = 13.82 kg/kg of fuel (c). 25% Oxygen C8H18 + 12.502 +37.5N2 =8C02 + 9H20 + 37.5N2 Theoretical Air/Fuel = 12.7 kg/kg of fuel 77 Natural Gas (a). Normal Air CH4 + 202 + 7.524N: = C0 + 2H 0 + 7.524N 2 2 2 Theoretical Air/Fuel = 17.24 kg/kg of fuel (b). 23!ic Oxygen CH4 + 202 + 6.71\: = C02 + 2H20 + 6.7N2 Theoretical Air/Fuel = 15.72 kg/kg of fuel (c). 25l!C Oxygen CH4 + 202 + 6N2 = C02 + 2H20 + 6N2 Theoretical Air/Fuel = 14.48 kg/kg of fuel The above calculation has showed that the air requirement is reduced by 9%-19% as oxygen content increased in the air for complete combustion of one kg. of fuel for liquid as well as gaseous fuels. This is one of the reason for reduction in volumetric efficiency with increased percentage of oxygen in the intake manifold of the engine. 78