1、Practical Diesel-Engine Combustion Analysis Bertrand D. HsuPractical Diesel-Engine Combustion Analysis Bertrand D. Hsu Society of Automotive Engineers, Inc. Warrendale, Pa. Copyright 2002 Society of Automotive Engineers, Inc. eISBN: 978-0-7680-4166-8All rights reserved. No part of this publication m
2、ay be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. For permission and licensing requests, contact: SAE Permissions 400 Commonwealth Drive Warrendale,
3、PA 15096-0001 USA Tel: 724-772-4891 Fax: 724-772-4028 E-mail: permissionssae.org Library of Congress Cataloging-in-Publication Data Hsu, Bertrand D. Practical diesel-engine combustion analysis / Bertrand D. Hsu. p. cm. Includes biographical references and index. ISBN 0-7680-0914-6 1. Diesel motorCom
4、bustion. 2. Diesel motorFuel systems. I. Title. TJ797 .H758 2002 621.436dc21 2002075825 SAE 400 Commonwealth Drive Warrendale, PA 15096-0001 USA Tel: 877-606-7323 (inside USA and Canada) 724-776-4970 (outside USA) Fax: 724-776-0790 E-mail: custsvcsae.org Copyright 2002 Society of Automotive Engineer
5、s, Inc. ISBN: 0-7680-0914-6 SAE Order No. R-327 Printed in the United States of America.Contents Acknowledgments vii Preface ix I 1.1 1.2 II 2.1 COMBUSTION AND FUEL-INJECTION PROCESSES IN THE DIESEL ENGINE 1 Diesel-Engine Fuel Injection and Spray Combustion 2 1.1.1 Kinetically and Diffusion-Controll
6、ed Combustion Phenomena in the Diesel Engine 2 1.1.2 Diesel-Engine Fuel-Injection Process 3 1.1.3 Spray Combustion in the Diesel Engine 6 DI Diesel-Engine Combustion Process 7 1.2.1 General Combustion Process 7 1.2.2 Ignition Delay Period 8 1.2.3 Kinetic or Premixed Burning Period 9 1.2.4 Diffusion
7、Burning Period 9 1.2.5 After Burning Period 10 References 10 HEAT RELEASE AND ITS EFFECT ON ENGINE PERFORMANCE 13 Calculating Heat Release 13 2.1.1 Heat-Release Calculation Basics 15 2.1.2 Cylinder-Charge Molar Change during Combustion 17 2.1.3 Cylinder-Pressure Data Smoothing and Calculation Interv
8、al 19 iiiPRACTICAL DIESEL-ENGINE COMBUSTION ANALYSIS 2.2 2.3 Heat Release, Relative Cycle Efficiency, and Peak Cylinder Pressure 21 2.2.1 Air-Cycle Analysis 21 2.2.2 Case of Combustion before Top Dead Center (TDC) 22 2.2.3 Case of Combustion after TDC 24 2.2.4 Relative Cycle Efficiency and Peak Cyli
9、nder-Firing Pressure 26 Pressure Data Collection for Heat-Release Calculation 30 2.3.1 Synchronization of Cylinder Pressure and Volume (TDC Correction) 30 2.3.2 Flush-Mounting the Pressure Transducer 33 2.3.3 Some Other Aspects Associated with Cylinder-Pressure Measurements 35 References 37 III 3.1
10、3.2 IV 4.1 COMBUSTION ANALYSIS ASSOCIATED WITH FUEL EFFICIENCY AND SMOKE 39 Fuel-Injection Related 39 3.1.1 Injector Hole Length versus Diameter (L/D) Ratio 39 3.1.2 Fuel-Injection Pressure 42 3.1.3 Injector-Flow Rate 45 3.1.4 Secondary Injection 47 3.1.5 Injector-Sac Volume 50 Combustion-Chamber Re
11、lated 53 3.2.1 Combustion-Chamber Bowl Shape 53 3.2.2 Injector-Spray Position 56 3.2.3 Combustion-Chamber Insulation 58 References 60 COMBUSTION ANALYSIS ASSOCIATED WITH NOX AND ROUGHNESS 61 NOX Emissions 61 4.1.1 NOX Formation 61 4.1.2 Injection-Timing Retard 64 4.1.3 Lower Inlet Air Temperature 69
12、 ivCONTENTS 4.2 V 5.1 5.2 VI 6.1 6.2 6.3 Index 4.1.4 Higher Compression Ratio, Lower Inlet Air Temperature, and Injection-Timing Retard 73 4.1.5 Water-Emulsified Diesel-Fuel Combustion 77 4.1.6 Higher Fuel-Injection Pressure 80 Combustion Roughness (Noise Emissions) 85 4.2.1 Origin of Combustion Rou
13、ghness 85 4.2.2 Measurement of Combustion Roughness 86 4.2.3 Sample of Combustion Roughness Comparison 88 References 91 COMBUSTION ANALYSIS OF VARIOUS OPERATION CONDITIONS 93 Effects of Fuel 93 5.1.1 Fuel Temperature Effect 93 5.1.2 Fuel Composition Effect 98 Effects of Inlet Air Manifold Condition
14、105 5.2.1 Inlet Manifold Air Temperature (MAT) Effect 105 5.2.2 Inlet Manifold Air Pressure (MAP) Effect 108 References 110 ALTERNATE FUELS COMBUSTION ANALYSIS 113 The High-Pressure-Injection Natural-Gas-Fueled Diesel Engine 113 “H-Process“ Natural-Gas Dual-Fueled Diesel-Engine Combustion. . . 116 C
15、oal-Water-Slurry-Fueled Diesel-Engine Combustion 123 6.3.1 CWS Ignition 125 6.3.2 CWS Combustion 127 6.3.3 Emissions of Coal-Fueled Engine Combustion 129 6.3.4 CWS Fuel Spray and Wall Impingement 129 6.3.5 Conclusions 130 References 131 135 About the Author 147 vAcknowledgments I wish to express my
16、deep appreciation to the General Electric Company for permission to use the many materials I had the opportunity to develop while working there. I would also like to acknowledge the Society of Automotive Engineering International and the American Society of Mechanical Engineers for permission to rep
17、roduce figures from their publications. viiPreface The diesel engine is one of the most efficient types of heat engines and is widely used as a prime mover for many applications. The most important process that determines the performance of the diesel engine is its combus- tion process. Since Rudolp
18、h Diesel invented the compression ignition engine more than a century ago, our knowledge of the combustion process has increased tremendously. In recent years, with the aid of computers, we have made great progress in the study of engine combustion modeling. As a result, our knowledge of the intrica
19、cies of the inner workings of engine cylinders has improved vastly. However, because of the complexities of the processes involved in the practical diesel engine, there are still too many unknowns that prevent computational predictions from having the accuracy level required by industry. Although pr
20、actical development engineers can benefit from the knowledge gained by combustion modeling, they still have to rely ultimately on the experimental development process to arrive at the final design. In the course of such development, it is important to understand how the hardware changes affect the e
21、ngine combustion process. In this sense, practical com- bustion analysis is a powerful tool. Heat-release analysis, which is based on actual, collected cylinder-firing pressure, is the essence of combustion analysis. A single-zone diagnostic type heat release (zero-dimension model) is used extensive
22、ly in this book. When used consistently, this calculation provides useful combustion cycle information. It can be used to understand not only the practical engine performance changes but also the direction for improvement. ixPRACTICAL DIESEL-ENGINE COMBUSTION ANALYSIS This book does not attempt to c
23、over all the possible design problems that a diesel engine engineer might meet. Rather, it demonstrates through many examples how to apply some basic combustion knowledge to understand the changes in engine performance. Practical heat-release analysis is also used to calibrate the specific engine co
24、mputational model at various stages to shorten the development process. Many of the materials within this text are associated with the medium-speed diesel engine, since this is the area in which I have the most experience. However, the methods used and the basic knowledge needed for other types of d
25、iesel engines should be similar. This text aims to help readers to analyze their own practical combustion prob- lems, not necessarily to provide ready solutions. Chapter 1 deals with some basic characteristics of diesel engine combustion process. Chapter 2 describes a commonly used tool to analyze c
26、ombus- tionheat-release analysis. The usefulness of heat-release analysis and some of the problems associated with acquiring the heat-release information are also included in this chapter. Chapters 3 and 4 discusses the materials that engineers encounter while conducting combustion design. Chapter 5
27、 describes the performance changes that might be encountered in the engine user environment. Finally, Chapter 6 covers the materials on some of the alternative fuel engines that I have had the opportunity to develop. I am greatly indebted to the General Electric Company, especially the Transportatio
28、n Systems division (GETS), where I had the opportunity to work on actual combustion problems in detail. In particular, I am grateful for the longstanding and unreserved support from the previous GETS man- agers, Martin J. Hapeman, John G. Hoffman, Thomas Hoover, and Robert F. Fischer. Their support
29、has made my work over the years possible. I am very grateful to Dr. Gong Chen and Dr. Paul Flynn of GETS for their encourage- ment in writing this book and their review of the original manuscript. I wish to express my deepest thanks to members of the GETS Diesel Engine Laboratory, especially to Dona
30、ld Lecker and Richard Beal, without whose help all the useful data in this book could not have been collected. My grat- itude also goes to those previously and presently with GE Corporate Research and Develeopment, Dr. Gary Leonard, Dr. Sudhir Savkar, Roger Johnson, and Eugene Kimura, for their supp
31、ort of my work over the years. In addition, I wish to acknowledge my alma mater, Tsinghua University of Beijing, China, where the foundation of this work began while I was teach- x PREFACE ing there. My many colleagues and fellow professors there were always helpful and provided me with enlightening
32、 discussions. Last, but not the least, I would like to thank my wife Jane for her unselfish support and patience for over forty-six years, without which I would not have had the chance to concentrate on my work. My son and daughter, Ning and Ann, have also strongly encouraged me to complete this boo
33、k and pro- vided me with considerable computer logistics support. I am truly grateful to them all. Bertrand D. Hsu xiI Combustion and Fuel-Injection Processes in the Diesel Engine The diesel engine is more appropriately called the compression ignition engine. Fuel ignition in the diesel engine is re
34、alized by the high temperature that results from the compression of the cylinder air charge. As is well known, diesel-engine combustion systems basically are of two kinds: direct injection (DI) and indirect injection (IDI). The high energy efficiency of the DI diesel engine has made it the dominant
35、type of diesel engine. This book focuses on the combustion analysis in the DI diesel engine, though some principles also apply to the IDI diesel engine. In DI diesel engines, fuel is injected into the engine cylinder in liquid form. To burn, the fuel must evaporate and mix with air to form a combust
36、ible mixture. Not all fuel can be burned at the same time. The combustion of diesel-engine spray is heterogeneous. It is a combination of partially pre- mixed and partially diffusive combustion. Each cycle involves ignition, combustion, and extinction processes. These phenomena are very complex and
37、their detailed mechanisms are not fully known. To better understand engine performance, some brief discussions of the basic types of combus- tion processes, as well as some fundamentals of fuel injection and fuel spray combustion, are helpful. 1 PRACTICAL DIESEL-ENGINE COMBUSTION ANALYSIS 1.1. Diese
38、l-Engine Fuel Injection and Spray Combustion 1.1.1. Kinetically and Diffusion-Controlled Combustion Phenomena in the Diesel Engine Most practical combustion phenomena are primarily controlled either by chemical kinetics or by diffusion, flow, and other physical mixing processes. If the fuel, oxidant
39、, and product of combustion are all in gas phase and uni- formly distributed, the combustion is said to be kinetically controlled. The rate of reaction at any given instance will be independent of location and the temperature will be uniform. Combustion in this case is determined by the rate of chem
40、ical kinetics. Reaction rate is a function of temperature, equiv- alence ratio, activation energy, and so on, as defined by the Arrhenius equa- tion. The diesel-engine ignition event, which happens after the injected fuel is evaporated and locally well mixed with surrounding air, can be considered a
41、 kinetically controlled phenomenon. The small amount of fuel burned immediately after ignition is premixed and mainly kinetically controlled. If the fuel, oxidant, and product of combustion are not spatially well-mixed before combustion, gradients of species and temperature will be established in sp
42、ace. Such gradients will cause conduction of heat and diffusion of species toward the regions of lower temperatures and concentrations, respectively. The combustion flame is located at some station in space. Reactants will dif- fuse into the flame zone, whereas the products and heat will diffuse awa
43、y from the flame zone. Such a poorly mixed combustion is said to be diffusion controlled. The rate of combustion is limited by the rates of diffusion. Gaseous-fuel flame is one well-known diffusion combustion type. When liquid fuel is burned, an additional physical evaporation process usually is inv
44、olved. The evaporation temperature of the fuel generally is lower than the self-ignition temperature of the fuel (vapor)-air mixture. Consequently, combustion occurs mainly in the gas phase. The chemical rate of reaction (dictated by chemical kinetics) is much faster than rates of evaporation, flow,
45、 diffusion, and mixing. This type of diffusion-controlled combustion is dominant in diesel-engine combustion. 2 COMBUSTION AND FUEL-INJECTION PROCESSES IN DIESEL ENGINES 1.1.2. Diesel-Engine Fuel-Injection Process Fuel injection has a dominant effect on DI diesel-engine combustion and performance. A
46、t the end of the 18th century, Dr. Rudolph Diesel tested his early diesel engine using compressed-air injection to atomize fuel. How- ever, an air-injection system cannot provide high injection pressure. In the early 19th century, the first airless, or solid, injection system was applied to the dies
47、el engine. Subsequent progress in diesel-engine development has been dependent largely on improvements in fuel injection. To comprehend engine combustion changes fully, we first must understand fuel-injection characteristics. Details of the fuel-injection process depend on fuel-system design specifi
48、cs. The following example analyzes the com- monly used jerk-pump-type diesel fuel-injection system. Figure 1.1 shows the schematics of such a system, which comprises a high-pressure fuel pump, delivery valve, fuel line, and an injector with spray holes. The vol- ume between the injector nozzle and t
49、he top of the plunger in the pump is called the high-pressure volume. When the filling port of the plunger and Figure 1.1 Typical jerk-pump fuel-injection system 3 PRACTICAL DIESEL-ENGINE COMBUSTION ANALYSIS barrel in the high-pressure fuel pump is closed, diesel fuel is compressed in the high-pressure volume. The pressure is transmitted to the injector end and forces open the needle valve when it exceeds nozzle-opening pressure.
