Design and Optimization of the Scavenging System of a Multi-Cylinder Two-Stroke Scotch-Yoke Engine

DESIGN AND OPTIMIZATION OF THE SCAVENGING SYSTEM OF A MULTI-CYLINDER TWO-STROKE SCOTCH-YOKE ENGINE

NG TEE NENG

UNIVERSITI TEKNOLOGI MALAYSIA DESIGN AND OPTIMIZATION OF THE SCAVENGING SYSTEM OF A MULTI-CYLINDER TWO-STROKE SCOTCH-YOKE ENGINE

NG TEE NENG

A thesis submitted in fulfilment of the requirements for the award of the degree of Master of Engineering (Mechanical)

Faculty of Mechanical Engineering Universiti Teknologi Malaysia

APRIL 2006

ABSTRACT

A two-stroke engine complete with a scavenging system, operating with external pumping mechanism is being developed. The engine comprises of two pair of combustion chambers and a pair of piston pumps that are integrated onto the Scotch-Yoke crank mechanism. The Schnurle type loop scavenging arrangement was selected for the scavenging arrangement for the engine port design. The pump was to be driven by the engine’s pistons linkages. The significant advantages of this opposed piston-driven pump concept is the double action of air pumping at every 180° interval of crankshaft revolution. In addition, extensive work using Computational Fluid Dynamic code simulation tools were applied throughout the project to ensure that the scavenging port geometry is optimized. Also developed was a scavenging test rig specifically to verify the simulation results. The unfired tracer gas sampling method was developed for the scavenging measurement purposes. The experimental testing was carried out successfully with the use of instrumentations such as Dewetron High Speed Data Acquisition and crank encoder. Both the simulation results and experimental results showed good scavenging characteristic, where the scavenging efficiency is closed to the perfect mixing scavenging model. The development of the scavenging system will allow for the reduction of the pollutant emission, and the overcome short-circuiting problem of the two-stroke engine.

ABSTRAK

Rekabentuk enjin dua lejang telah dibangunakan dengan sistem hapus-sisa lengkap, di mana ia beroperasi dengan pengepaman udara dari luar. Rekabentuk enjin ini adalah berpandukan mekanisme Scotch-Yoke yang beroperasi dengan dua pasang kebuk pembakaran dan sepasang pemampat piston. Susunan sistem hapus- sisa jenis “Schnurle” telah dipilih untuk mereka pembukaan udara dalam enjin. Pam ini dipandu secara terus oleh penyambungan omboh yang bersalingan. Kelebihan mekanisme yang ketara ialah ia dapat menghasilkan dua kali kerja pengepaman pada setiap 180° putaran aci engkol. Tambahan lagi, kajian yang mendalam pada bahagian penukaran udara telah dijalankan dengan kod program computer Computational Fluid Dynamic untuk memastikan rekabentuk pembukaan udara dalam keadaan yang memuaskan. Sementara itu, rangka uji-kaji sistem hapus-sisa telah dibangunkan untuk mengesahkan nilai keputusan daripada simulasi komputer. Teknik pengambilan jenis gas dalam keadaan tanpa bakar, telah dijalankan dengan kelengkapan alat pengukuran seperti Dewetron High Speed Data Acquisition dan pengecod engkol. Kedua-dua keputusan daripada simulasi komputer dan ujikaji telah menunjukkan kecekapan hapus-sisa dalam keadaan yang baik, di mana nilainya adalah menghampiri model hapus-sisa yang sempurna. Pembangunan sistem hapus- sisa ini telah menjamin keberkesanannya dalam mengurangkan hasil kotoran daripadan pembakaran dalam enjin dan juga menyelesaikan masalah short-circuiting rekabentuk enjin jenis dua lejang.

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TABLE OF CONTENT

CHAPTER CONTENT PAGE ABSTRACT v ABSTRAK vi TABLE OF CONTENT vii LIST OF FIGURES xi LIST OF TABLES xv LIST OF APPENDICES xix

1 INTRODUCTION 1.1 Preface 1 1.2 Objectives 2 1.3 Statement of Problem 2 1.4 Hypotheses 2 1.5 Scopes 3 1.6 Methodology 4 1.6.1 Literature Review 5 1.6.2 Design Concept 5 1.6.3 Calculations and Analysis 5 1.6.4 CFD Simulations 6 1.6.5 Development of a Scavenging system Test Rig 6 1.7 The Gantt Chart 7

2 LITERATURE STUDY 2.1 Internal Combustion Engines 8

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2.2 Two Stroke Engine 10 2.3 The Scotch-Yoke Mechanism 12 2.3.1 The Differences between Scotch-Yoke Engine and Conventional Engine 13 2.3.2 Advantages of Scotch-Yoke Engine 15 2.3.2.1 Size Reduction 15 2.3.2.2 Engine Balance 17 2.3.2.3 Noise, Vibration and Harshness (NVH) 18 2.3.2.4 Emission 19 2.3.2.5 Efficiency 20 2.3.2.6 Cost 21 2.4 Scavenging Process 22 2.4.1 Cross-Scavenged 23 2.4.2 Loop-Scavenged 24 2.4.3 Uniflow-Scavenged 26 2.5 Scavenging Parametric 28 2.6 Scavenging Mathematical Models 31 2.7 Scavenging Measurement Methods 33 2.7.1 The Global Parameters Measurement Method 34 2.7.2 The Running Engine Parameter Measurement Method 35 2.7.3 The Computer Simulation Method 36 2.8 Supercharger 38 2.9 Future Challenges of Two-Stroke Gasoline engine 39

3 ENGINE DESIGN CONCEPT 3.1 Introduction 42 3.2 Scavenging System Design 43 3.2.1 Scavenging Arrangement 45 3.2.2 External Pump Design 46

4 CALCULATIONS AND ANALYSIS 4.1 Engine Component Design 50 4.1.1 Crankcase and Cylinder Block 51 4.1.2 Cylinder Liner s 53 4.1.3 Cylinder Head 56 4.1.4 Chamber 56 4.1.5 The Intake and Exhaust Manifold 58 4.1.6 Reed Valves 59 4.1.7 Piston Pump Design 60

4.2 The Scotch-Yoke Crank mechanism 62 4.2.1 Sliders 62 4.2.2 C-plates 65 4.2.3 Piston Heads 66 4.2.4 Crankshaft 67

5 FLOW SIMULATION AND ANALYSIS 5.1 Introduction 71 5.2 Flow Pattern Static Condition Analysis 73 5.2.1 The Main Port Design 75 5.2.1.1 The Simulation Results 78 5.2.1.2 Conclusion of the Main Port Design Simulation results 88 5.2.2 The Upsweep Design 88 5.2.2.1 The Simulation Results 90 5.2.2.2 Conclusion of the Upsweep Angle Design Simulation results 100 5.3 Analysis of the Simulated Scavenging Process 100 5.3.1 The Simulation Results 107 5.3.1.1. Velocity distribution 107 5.3.1.2. Species Transport Mass Fraction Distribution 112 5.3.2 Discussion on the Dynamic Simulation Results 117

6 FABRICATION OF A SCAVENGING SYSTEM TEST RIG 6.1 Introduction 121 6.2 The Test Rig Components 122 6.3 The Test Rig Set-Up 129 6.3.1 The Scavenging Measurement Results 134 6.4 The Pressure Inside Cylinder 140 6.4.1 Results of Pressure-In-Cylinder Analysis 141 6.5 Scavenging Performance Analysis 147

7 CONCLUSIONS & RECOMMENDATIONS FOR FURTHER WORK 7.1 Conclusions 149 7.2 Recommendation for Further Works 151

REFERENCES 152

APPENDICES 156

LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.0 Flow chart of project implementation 4 2.1 The different types of reciprocating engine 9 2.2 The two-stroke SI engine operating cycle with crankcase compression 11 2.3 The gas exchanges process of the crankcase compression Two Stroke Engine 11 2.4 The crank mechanism of a Scotch-Yoke engine 12 2.5 The application of the SYTech Engine 14 2.6 The comparison of the Scotch-Yoke engine with the conventional horizontal opposed cylinder engine 17 2.7 The 2 nd order noise level of the CMC 422 SYTech engine at WOT acceleration Cabin Noise 19 2.8 The results of SYTech Fuel consumption and NOx Emissions advantages compare to conventional engine 20 2.9 The comparison of mechanical losses of the CMC 422 Scotch-Yoke and the conventional boxer engine 21 2.10 The comparison percentage of total Engine costs between the CMC 422 SYTech and conventional engine 22 2.11 Scavenging arrangements 24 2.12 Various port plan layout of Schnurle type loop scavenging 26 2.13 Physical representation of isothermal scavenge model 28 2.14 a) Perfect displacements scavenging; b) Perfect mixing scavenging 31

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2.15 Benson-Brandham model of trapping characteristic 33 2.16 Schematic diagram of single-cycle scavenge rig with cylinder block for externally scavenged three cylinders engine in place 35 2.17 The PIV on the two-stroke engine 36 2.18 The 3D mesh with inlet and exhaust ducts 37 2.19 A supercharged and turbocharged fuel injected two-stroke engines 38 2.20 The Piston pumps 39 2.21 The future development of a two-stroke engine 40 3.1 Design of a Two-stroke Horizontal Opposed Scotch-Yoke Engine 44 3.2 The Schnurle loop scavenging 46 3.3 The Piston pump mechanism design 48 3.4 The scavenging process 49 4.1 The cylinders arrangement 52 4.2 The main cylinder block design 52 4.3 Cylinder liner design 53 4.4 Port openings timing 54 4.5 The height of the transfer ports and exhaust port 55 4.6 The cylinder head design 56 4.7 The detail of the hemi-spherical chamber design 57 4.8 The intake manifold design 58 4.9 The exhaust manifold design 59 4.10 The overview of the reed valve assembly 60 4.11 The two ways control by the reed valve design 60 4.12 The piston pump liner design 61 4.13 The volume A and B inside the piston pump 63 4.14 The rotational motion of the slider 64 4.15 The assembly of a pair of the slider and bearings 64 4.16 The C-plate design 65 4.17 The assembly of slider bearing with C-plate 66 4.18 The piston head for combustion process 67 4.19 The piston head for piston pump 67

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4.20 The Crankshaft design 68 4.21 The analysis of the crankshaft balancing 69 5.1 Flowchart of the flow pattern static state analysis. 74 5.2 Schnurle type loop scavenging design 76 5.3 The simulation results of sample A 79 5.4 The simulation results of sample B 81 5.5 The simulation results of sample C 82 5.6 The simulation results of sample D 84 5.7 The simulation results of sample E 85 5.8 The simulation results of sample F 87 5.9 The sweep port design 89 5.10 The design of the upsweep degree of the port 89 5.11 The simulation results of the sample 1 91 5.12 The simulation results of the sample 2 93 5.13 The simulation results of the sample 3 94 5.14 The simulation results of the sample 4 96 5.15 The simulation results of the sample 5 97 5.16 The simulation results of the sample 6 99 5.17 Flow chart for flow simulation in Fluent v 6.1 100 5.18 The engine computational symmetrical domain 102 5.19 The piston surface (moving wall) of the scavenging process 103 5.20 The convergence of the simulation Work 106 5.21 Velocity contour at 111.6° ATDC and at 136.6° ATDC 108 5.22 Velocity contour at 161.6° ATDC and at 186.6° ATDC 109 5.23 Velocity contour at 211.6° ATDC and at 236.6° ATDC 110 5.24 Velocity contour at 261.6° ATDC and at 271.6° ATDC 111 5.25 Mass Fraction at 111.6° ATDC and at 136.6° ATDC 113 5.26 Mass Fraction at 161.6° ATDC and at 1866° ATDC 114 5.27 Mass Fraction at 211.6° ATDC and at 26.6° ATDC 115 5.28 Mass Fraction at 261.6° ATDC and at 271.6° ATDC 116

5.29 The Mass fraction gas O2 versus crank angle 118 5.30 The Scavenging efficiency versus scavenging ratio 120 5.31 The trapping ratio versus scavenging ratio 120

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6.1 The gasket sealing and leakage inspection 122 6.2 Leakage inspection with soap bubble 123 6.3 The machined items of the engine crank mechanism 125 6.4 The perspex material representing the intake manifold 125 6.5 The associated reed valves and cylinder head section 126 6.6 The overview of the motorized scavenging test rig 126 6.7 The gas analyzer probe and Oliver IGD gas analyzer 128 6.8 The Dewetron signal display and crank angle sensor 128 6.9 Digital manometer and Tachometer 129 6.10 Schematic diagram of the scavenging test rig set up 130 6.11 The scavenging measurement arrangement 131 6.12 The gas analyzer probe on the outflow of the system 132 6.13 The illustration of the scavenging measurement 133

6.14 The pressure inlet, P 1 versus Engine speed, (rpm) 134

6.15 The Inlet velocity, V 1 versus Engine Speed (rpm) 136

6.16 The pumping manifold Pressure, P 2 versus Engine Speed 137

6.17 The pumping manifold velocity, V2 versus Engine Speed 138 6.18 The trapped volume ratio of Gas O2 versus Engine Speed 139 6.19 Schematic diagram of the pressure in-cylinder measurement 140 6.20 The location of the mounting of the pressure transducer 141 6.21 Pressure Variation in chamber A versus crank Angle 143 6.22 Pressure Variation in chamber B versus crank angle 145 6.23 Pressure Variation in piston pump chamber versus crank angle 146 6.24 The scavenging efficiency versus scavenging ratio 148 6.25 The trapping ratio versus scavenging ratio 148

LIST OF TABLES

TABLE NO. TITLE PAGE

1.1 The Gantt Chart 7 2.1 The dynamic mechanism equation differences between Conventional and Scotch-Yoke engine 15 2.2 The Packing Advantages between SYTech and Conventional engine 16 2.3 Classification of different scavenging methods and their applications 27 2.4 The typical values for the scavenging performance 30 2.5 The fields of application of spark ignition two-stroke and four-stroke engine 41 3.1 Typical engine specifications 43 3.2 Prediction performance for 4 cylinders 500cc Scotch-Yoke Engine 43 5.1 The several viscosity model application in the CFD simulations 72 5.2 The Engine Computation Domain Detail 74 5.3 The Operation parameters for the Cosmos FloWork 2004 75 5.4 Several samples of the main ports design 77 5.5 The study of the upsweep angle, (°) of the transfer port 90 5.6 Specification of the optimized Schnurle loop scavenging design. 100

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5.7 The set up parameters when using Fluent v6.1 104 5.8 The simulation conditions for the scavenging process analysis 105 5.9 Results of mass fraction 117 5.10 The dynamic results for the scavenging parameter 118 5.11 The standard data for the perfect mixing and displacement scavenging model 119 6.1 Bill of Material for the engine model design 124 6.2 Specification of the instrumentations 127 6.3 The experimental results for volume A and volume B 147

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LIST OF SYMBOLS

Yconv = Piston replacement for conventional engine, m

Ysy = Piston replacement for Scotch-Yoke engine, m vconv = Piston Velocity for conventional engine, m vsy = Piston Velocity for Scotch-Yoke engine 2 aconv = Piston acceleration for conventional engine, m/s 2 asy = Piston acceleration for Scotch-Yoke engine, m/s r = Crank radius, m L = Conrod length, m α = Crank angle after top dead center (TDC) ω = Angular speed of the crankshaft, ˚ SE = Scavenging Efficiency TE = Trapping Efficiency CE = Charging Efficiency SR = Scavenging Ratio

Vi = Intake velocity, m/s d = Cylinder bore, mm l , s = Stroke, mm 3 Vet = Swept volume from TDC to exhaust opening, mm 3 Vto = Total volume in the engine cylinder, mm 3 Vtr = Trapped volume during TDC, mm tl = Liner thickness, mm N = Engine speed, rpm 2 σc = Permissible value of tension, 200 kgcm , Cast Iron 2 Pm = Maximum combustion pressure, 49.07 kg.cm

D l = Inner liner diameter, mm

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n = 1 for two stroke engine Q = Capacity/cylinder, mm 3

ηv = Volumetric efficiency 2 A = area, mm h = Height, mm

Fi = Inertia Force, N

Mi = Moment Inertia, Nm mu = Unbalanced mass, g rm = Radius of unbalanced mass from center, mm

Ld = The distance from center, mm rb = The distance of mass gravity of counterweight, mm

Mref = The unbalance Moment Inertial System, Nm AM = Angle for main port, ˚ MT = Target point for main point, mm UPM = Upsweep angle of main port, ˚ UPR = Upsweep angle of rear port, ˚ UPS = Upsweep angle of side port, ˚ DPE = Downsweep angle of exhaust port, ˚ ρ = Density, g/ml TDC = Top Dead Center BDC = Bottom Dead Center ATDC = After Top Dead Center, ˚ γ = Specific heat ratio σ = Turbulent Prandtl numbers k = Turbulent kinetic energy ε = Dissipation rate of turbulent kinetic energy atm = Pressure at atmosphere condition CA = Crank angle, ˚

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LIST OF APPENDICES

APPENDIX TITLE PAGE

A Balance Shaft Design 157 B1 Orthographic view 158 B2 Exploded View of Engine Model 159 B3.1 Slider R 160 B3.2 Slider L 161 B3.3 Slider Bearing 162 B3.4 Slider Bearing 2 163 B3.5 Crankshaft bearing with thrust 164 B3.6 Crank Bearing M 165 B3.7 Crankshaft 166 B3.8 Crankcase 167 B3.9 Exhaust Manifold 168 B3.10 Crankshaft Bearing 169 B3.11 Intake manifold 170 B3.12 C-platrigmodel1 171 B3.13 C-platrigmodel2 172 B3.14 Piston55K 173 B3.15 Compression rig2 174 B3.16 Piston pump 175 B3.17 Sleeve test 176 B3.18 Reed main body 177 B3.19 Cylinder head 178 B3.20 Block 179

B3.21 Linearslide 180 B3.22 Adapter block 181 C Dynamic Mesh Option Set Up 182 D Scavenging Rig Experimental Data 184 E Dewetron Signal Display Setting 188 F Pressure In-cylinder Data 189 G Tube Adaptor Specifications 194

CHAPTER 1

INTRODUCTION

1.1 Preface

The emphasis of the research project is to design a scavenging system for a newly conceptualized small capacity (500 cc), multi-cylinder, two-stroke engine based on the Scotch-Yoke mechanism. The research work on the Scotch-Yoke engine concept was attempted by CMC SYTECH Corp. of Australia [2] and was proven to have several advantages i.e. small size, perfect balance, reduction of the engine weight compare to the conventional reciprocating engine of a same displacement.

The scavenging process in the two-stroke cycle engine has direct influent on the performance of their combustion processes and remains one of the fundamental important strategies towards improvement of fuel utilization efficiency and the reduction of pollutant.

Several C FD simulation analyses have been done to characterize the scavenging process for the port geometry optimization. In addition, an unfired test rig for scavenging system measurement has been developed in conjunction with this research work.

1.2 Objectives

The objectives of the research project are:

i. To design an external scavenging system of a two stroke Scotch-Yoke multi- cylinder engine ii. To develop a scavenging system test rig to optimize the scavenging process. iii. To reduce fresh charge short-circuiting problem in the two-stroke engine.

1.3 Statement of Problem

Scavenging process is required in two-stroke engines in assuring the appropriateness of combustion. However it will also result in the short-circuiting of fresh charge (flow directly from the engine’s transfer to the exhaust port). The short- circuiting phenomenon is responsible for the low fuel economy/efficiency and high- unburned hydrocarbons emission.

1.4 Hypothesis

An external scavenging system is required to retrofit the small capacity multi- cylinder, two-stroke horizontally opposed Scotch-Yoke engine to improve its scavenging efficiency and overcome the mixture short-circuiting problem.

1.5 Scope

The scopes of work prescribed are as follows:

i. Literature reviews on the two-stroke engine, scavenging systems and Scotch-Yoke engine concept ii. Design of a scavenging system for the two-stroke Scotch-Yoke engine. iii. Computational Fluid Dynamic(CFD) code simulation for the scavenging flow analysis iv. Development of an unfired scavenging system test rig v. Validation of the hypotheses

1.6 Methodology

The methodology applied in the implementation of this project was as follows:

Literature study

Design Concept

Calculations and Analyses

CAD Solid Drawing s

CFD simulations

Results CFD Database Evaluation

Optimized

Development of an unfired Scavenging system test rig

Documentations and Reports

Figure 1.0: Flow chart of project implementation.

1.6.1 Literature Review

The review of recent works is important to provide the understanding of the advancements of two-stroke technologies such as the scavenging systems and Scotch-Yoke engine design itself. The previous technical references which are published in the reputable journals such as Engineering Society for Advancing mobility Land Sea, Air and Space (SAE) Technical Paper Series, will assist the author in providing new research methods for the scavenging system development. Besides, there are several books and publications on two-stroke engines which will provide first hand knowledge on approaches to engine design and analysis.

1.6.2 Design Concept

With the knowledge obtained from literature study, a design concept of an external scavenging system which is suited to the design of Scotch-Yoke mechanism, as well as piston pumps design will be proposed. The loop scavenging arrangement, which is suitable for small capacity gasoline type two-stroke engine, will then be applied for the scavenging port geometry design work.

1.6.3 CAD Solid Drawings

It is in the opinion of the author that Computer-Aided Design ( CAD ) software, (e.g. SolidWorks 2004) is suitable tool to enable engine parts be designed and eventually developed. The specification of the engine parts will be shown in intricate details in finalizing engineering drawings.

1.6.4 CFD Simulations

The Computational Fluid Dynamic (CFD) simulation work is an important approach to predict the characteristic of the gas exchange processes particularly during the scavenging process. The design of the porting will be improved through the analysis of a series of simulation results.

1.6.5 Development of an Unfired Scavenging System Test Rig

The fabrication works of the unfired scavenging system test rig was done with the assistance of a local engineering company. Prior to this, the engine components detail drawings are prepared for the fabrication works. However, the assembly of the components into a complete unit was not made by the said company, but was made by the author in UTM , specifically at the Automotive Development Center (ADC) .

After the engine model was completely assembled, it was simulated for motion analysis using a specially designed motorized control system. The instrumentations for the scavenging measurement were installed at the engine model. A technique call gas sampling method was applied to evaluate for the engine’s overall scavenging system efficiency.

1.7 Gantt Chart

Planning and execution of the project indicates the milestone of the progress of the design and development work within 5 semesters.

Table 1.1: The Gantt chart Planning and Execution Semesters 1 2 3 4 5 1. Literature Review Study on the previous technical paper 2. Design Concept Develop the design concept

1. Engine geometry design 3. Calculations and Analyses 2. External pump design 4. CAD Solid Drawings 3D model drawing for the system 5. CFD simulations CFD code simulation for the design optimization 6. Fabrication works Fabrication of the engine model 7. Test Rig Setting Up 1. Setting up the test rig 8. Experimental data analysis Investigation on the Scavenging efficiency 9. Documentations and Reports Summary of the Project

Planned & Execution Extend For Execution 7

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