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Thermodynamic Analysis of Indirect Injection Diesel

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Thermodynamic Analysis of Indirect Injection Diesel THERMODYNAMIC ANALYSIS OF INDIRECT INJECTION DIESEL ENGINE OPERATION by Mostafa M. Kamel B.Sc., M.Sc., D.I.C. Thesis submitted for the degree of Doctor of Philosophy in the Faculty of Engineering of the University if London • 1977 Department of Mechanical Engineering, Imperial College of Science and Technology, London SW7 2BX To my MOTHER ABSTRACT An investigation is presented which analyses, both theoretically and experimentally, the operation of the Indirect Injection Diesel Engine. A computer program was developed to mathematically simulate the thermodynamic processes involved in the operation of the indirect injection diesel engine. The quasi-steady filling and emptying approach was employed to describe gas flow and changes in thermodynamic conditions. Numerical techniques were used to integrate the governing equations describing the engine thermodynamics along equal crank angle increments over the full engine cycle. In the simulation program a correlation was developed for heat flux calculations. This was based on a Nu-.Re relationship, in which velocity estimates representative of the chamber charge are obtained via the kinetic energy conservation concept. The correlation provided good predictions of heat fluxes in the cylinder and the prechamber when compared with measured behaviour. The discharge coefficient of the connecting passage was found to be dependent on its shape. It was also found to be a function of the flow direction and pressure ratio. The effect of piston proximity was also investigated and accounted for. Ignition delay periods were measured and correlated to chamber condi- tions. Both physical and chemical parts of the delay were considered. An extensive experimental programme has been carried out to obtain steady state data for the engine under test. From the measured pressure diagrams of both chambers, rate of heat release curves were calculated. These were used in conjunction with the cycle analysis program to evaluate -2- engine performance. The simulation program was finally used to isolate and quantify losses in the indirect injection diesel engine, and investigate the sources of its high specific fuel consumption in relation to the direct injection engine. -3- ACKNOWLEDGEMENTS The author would like to express his sincere gratitude to Dr. N. Watson for his advice and guidance while supervising this work. The help and advice of Drs. M. Marzouk and B. Holness, during the writing of the thesis, are also appreciated. Thanks are also due to Mr. R.D. Bloxham and the technical staff of. the Thermal Power Section, for their help throughout the experimental part of the work. The author is also grateful to Miss S. Chambers for careful and rapid typing of the manuscript. -4- LIST OF CONTENTS Page Abstract 1 Acknowledgements 3 List of Contents 4 Notation 9 CHAPTER 1: INTRODUCTION 15 1.1 Indirect Injection Diesel Engine Characteristics 15 1.2 Previous Work on Indirect Injection Diesel Engines 17 1.2.1 Engine performance and combustion 18 1.2.2 Ignition delay 23 1.2.3 Heat transfer 23 1.2.4 Exhaust emissions and noise 24 1.2.5 Engine simulation 27 1.3 Objectives and Outline of the Present Work 28 CHAPTER 2: TEST RIG AND DATA ACQUISITION SYSTEMS 30 2.1 Introduction 30 2.2 The Engine Test Bed 31 2.3 Overall Performance Variables 33 2.3.1 Engine power 33 2.3.2 Manifold Conditions 33 2.3.3 Fuel and air flows 33 2.4 Detailed Instrumentation 34 -5- Page 2.4.1 Pressure measurements 34 2.4.2 Position measurements 36 2.4.3 Combustion chamber wall temperatures and instantaneous heat flux measurements 37 2.5 Data Acquisition Systems 37 2.5.1 Link to on-line computer 37 2.5.2 Tape recorder system 41 2.6 Test Program 45 CHAPTER 3: ENGINE SIMULATION 46 3.1 Introduction 46 3.2 Basic Thermodynamic Relations Involved 48 3.3 The Mathematical Simulation Technique 53 3.4 The Numerical Solution 56 3.4.1 The numerical method .57 3.4.2 Rate of heat release program 58 3.4.3 Full cycle analysis program 61 CHAPTER 4: HEAT TRANSFER 66 4.1 Introduction 66 4.2 Convective Heat Transfer 67 4.2.1 Gas velocity measurements 69 4.2.2 Gas velocity calculations 71 4.2.3 The experimental investigation by Hassan 74 4.2.4 Present calculation method of gas velocity 78 -6- Page 4.2.4.a Kinetic energy and momentum conservation concepts 78 4.2.4.b Energy dissipation 80 4.2.4.c Method of calculation 84 4.2.4.d Induced velocity due to fuel jet 89 4.2.5 Comparisons with Hassan's results 92 4.2.6 Conclusions 98 4.3 Radiative Heat Transfer 99 4.3.1 Review of available work 99 4.3.2 Calculation procedure 102 4.4 Heat Flux Measurements 108 4.4.1 Test arrangement 108 4.4.2 Analysis of experimental results 112 4.4.3 Measured heat fluxes and temperatures 114 4.5 Comparison of Measured and Predicted Heat Flux and Conclusions •128 4.5.1 Motored operation 128 4.5.2 Fired operation 132 CHAPTER 5: PASSAGE COEFFICIENT OF DISCHARGE 143 5.1 Introduction 143 5.2 Review of Published Work on Discharge Coefficient . Calculations 144 5.3 Discharge Coefficient Calculations 149 5.3.1 Sharp edged orifice 150 5.3.2 Thick orifice 158 5.3.3 Conclusions 164 -7- Page 5.4 Experimental Investigation 165 5.4.1 Test rig 165 5.4.2 Test conditions and results 167 5.5 Conclusions 171 CHAPTER 6: IGNITION DELAY 172 6.1 Introduction 172 6.2 Definitions of Ignition Delay • 173 6.3 Review of Ignition Delay Correlations 175 6.3.1 Ignition theories and foundations of reaction kinetics 175 6.3.2 Wolfer's correlation 178 6.3.3 Sitkei's correlation 180 6.3.4 Tsao's correlation 181 6.3.5 Ilmari's correlation 181 6.4 Ignition Delay Measurements 184 6.4.1 Test installation 184 6.4.2 Injection and ignition moments 186 6.4.3 Test results and discussion 187 6.5 Ignition Delay Correlation 192 6.5.1 The physical delay 195 6.5.2 Final correlation 202 6.5.3 Conclusions 205 CHAPTER 7: EVALUATION OF SIMULATION TECHNIQUE 207 7.1 Introduction 207. -8- Page 7.2 Experimental Results 207 7.3 Calculated Heat Release Diagrams 215 7.4 Comparisons of Predicted and Measured Performance 232 7.4.1 Fuel consumption • 232 7.4.2 Pressure and pressure difference diagrams 234 7.4.3 Motoring and friction mean effective pressures 243 7.5 , Combustion Chamber Interaction 246 7.6 Conclusions 257 CHAPTER 8: INDIRECT INJECTION DIESEL ENGINE PERFORMANCE IN RELATION TO THE DIRECT INJECTION DIESEL 258 8.1 Introduction 258 8.2 Loss Isolation Technique 258 8.3 Motored Engine Operation 262 8.4 Fired Engine Operation 268 8.5 Combustion Mode Considerations 285 8.6 Conclusions 291 CHAPTER 9: CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK 293 APPENDICES A. Effect of Thermal Shock on Cylinder Pressure Transducers 298 B. Exhaust Emissions Measurements 305 REFERENCES 309 -9- NOTATION Unless otherwise stated in the text, symbols are defined as follows; Symbols a, a a Constants l' 2 A Geometric or heat transfer area A Instantaneous liner area L A Passage geometric area A Cylinder liner area at TDC TDC b, bl, b2 Constants B Boltzmann number o c, cl, c2 Constants C Contraction coefficient c C Discharge coefficient d Discharge coefficient of injector nozzle Cd inj C f Friction torque coefficient C. Incompressible contraction coefficient C Current jet centre-line concentration m C o Initial jet centre-line concentration (1.0) CP Specific heat at constant pressure . C r Condentration at any jet core radius C Half radius concentration r) 2 d. Injector nozzle diameter D Characteristic dimension c D Cylinder bore e D Vena contracta diameter v e Internal energy E Activation energy a -10- E r Radiation energy f Force defect coefficient f f Wave fundamental frequency f. Incompressible force defect coefficient f s Stoichiometric (Fuel/Air) ratio F Equivalence ratio F d Force defect G Swirl speed ratio (co g/wd) h Instantaneous heat transfer coefficient h f Heat of reaction of fuel hg Gas enthalpy H L Percentage heat loss to total fuel H r Percentage heat loss relative to IDI engines K. Gas thermal conductivity K a Absorption coefficient K n Orifice flow constant K s Average absorption coefficient K s Average absorption coefficient at atmospheric pressure Physical depth Wall thickness w L Radiation length L Connecting rod length e Lop Optical depth Mass Mass flow rate m Cumulative products of fuel combustion in the control f volume m Cumulative gas flow g m. Gas mass flow rate M Charge mass Ma Initial trapped mass of air 0 Mass of fuel burnt Mb Mf Initial trapped mass of fuel products l o M Initial trapped mass o N Engine speed Nu Nusselt number partial pressure P Pressure 13° Rate of change of pressure P Back pressure b P Exhaust manifold pressure exh P. Injection pressure P Inlet manifold pressure inl P Total pressure upstream o P Pressure ratio (downstream/upstream) r P Pressure at orifice.wall w Q Total heat flux Radiant heat flux Qr Qw Heat flux to the wall r Pressure ratio across the orifice (static-static) r Critical pressure ratio c r Radius of rotating disc d r Engine crank radius e r. Any radius inside jet core R Gas constant Re Reynolds number Re Reynolds number for rotating disc d R. Outer radius of jet cross section -12- R Radius of approach pipe 1 R Radius of the orifice 2 S Arc distance travelled by the jet a S Width of rotating disc enclosure d S Engine stroke e S.
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