Diesel Engine Transient Operation By Constantine D. Rakopoulos and Evangelos G. Giakoumis

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Diesel Engine Transient Operation By Constantine D. Rakopoulos and Evangelos G. Giakoumis

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Preface

Traditionally, the study of internal combustion engines operation has focused on
the steady-state performance. However, the daily driving schedule of automotive
and truck engines is inherently related to unsteady conditions. In fact, only a very
small portion of a vehicle’s operating pattern is true steady-state, e.g., when
cruising on a motorway. Moreover, the most critical conditions encountered by
industrial or marine engines are met during transients too. Unfortunately, the
transient operation of turbocharged diesel engines has been associated with slow
acceleration rate, hence poor driveability, and overshoot in particulate, gaseous and
noise emissions. Despite the relatively large number of published papers, this very
important subject has been treated in the past scarcely and only segmentally as
regards reference books. Merely two chapters, one in the book Turbocharging the
Internal Combustion Engine by N. Watson and M.S. Janota (McMillan Press,
1982) and another one written by D.E. Winterbone in the book The
Thermodynamics and Gas Dynamics of Internal Combustion Engines, Vol. II
edited by J.H. Horlock and D.E. Winterbone (Clarendon Press, 1986) are dedicated
to transient operation. Both books, now out of print, were published a long time
ago. Then, it seems reasonable to try to expand on these pioneering works, taking
into account the recent technological advances and particularly the global concern
about environmental pollution, which has intensified the research on transient
(diesel) engine operation, typically through the Transient Cycles certification of
new vehicles.
For a number of years now, the vast majority of diesel engines have been
turbocharged and this trend is sure to continue. Although turbocharging the diesel
engine is beneficial because it increases its (specific) brake power, and also
because it provides better fuel economy and reduced CO2 emissions, it is the
turbocharged diesel engine that suffers way more than its naturally aspirated
counterpart from poor transient response. This originates in what is known in the
engine community as ‘turbocharger lag’, which is the key factor responsible for the
slow speed response and heavy exhaust emissions. Consequently, the turbocharged
diesel engine will be the focus of analysis in this book, with the behavior of its
naturally aspirated counterpart highlighted only on specific aspects (e.g., cold
starting). As a matter of fact, the title of the book could well have read
Turbocharged Diesel Engine Transient Operation.
Although there are many operating schedules experienced by diesel engines
that can loosely be termed transient, we have focused on the most influential ones
in terms of engine performance and exhaust emissions, namely load acceptance,
acceleration and cold starting, as well as their combinations, most notably in the
form of Transient Cycles.
Emphasis in the book is placed on the in-cylinder thermodynamic
discrepancies, exhaust emissions and methods of improving transient response.
However, it has been our intention to cover the subject from all relevant aspects;
consequently, the interested reader will be able to find information on areas of
‘lesser popularity’ such as second-law (exergy, availability) analysis, compressor
surging or crankshaft torsional deformation during transients. Although automotive
applications are usually the main case studied, industrial or marine engines’
transient response is dealt with too. Moreover, the analysis is thermodynamics
rather than control oriented. Control matters are only briefly discussed, mainly in
Chapter 6, where the effects of the various control strategies on the engine transient
response improvement are pinpointed.
The book is organized as follows: in Chapter 1, an introduction to transient
diesel engine operation is given, highlighting various typical load acceptance and
acceleration schedules of both automotive and industrial/marine engines, and
detailing the importance and different evolution pattern of transient operation
compared with steady-state conditions. Chapter 2 describes the complex
thermodynamic issues of transient operation (located in the fuel injection
mechanism, heat transfer, combustion, air-supply and exhaust gas recirculation
processes), starting, of course, with the discussion of the fundamental turbocharger
lag problem. Chapter 3 focuses on the dynamic issues encountered during
transients, namely friction overshoot, components stress and crankshaft torsional
deformation. Chapter 4 discusses briefly the experimental procedure involved in
transient diesel engine research, addressing in more detail the instantaneous
particulate matter measurement techniques and the heat release analysis of
transient pressure data. Chapter 5 deals with the very important aspect of exhaust
emissions during transients, and Chapter 6 with the various methods developed
over the years for reducing the turbocharger lag phase and improving transient
response. Chapter 7 focuses on other aspects of transient conditions, namely cold
starting, operation when the turbocharger compressor experiences surge and lowheat
rejection engine operation. Chapter 8 provides an alternative coverage of the
subject through the perspective of the second law of thermodynamics. Finally,
Chapter 9 summarizes the various modeling approaches developed over the years
for the simulation of transient operation.
This book is the outcome of many years of research on the subject and it is
intended to serve as a reference for engineers and researchers but it should also be
useful to (post-graduate) students as a supplementary text. It is expected that the
reader is already familiar with (basic) aspects of internal combustion engine
operation. Consequently, when dealing, for example, with the combustion
development during transients, only a brief reminder is provided at the beginning
of the section concerning some fundamental features of (steady-state) combustion,
and afterwards we focus on the discrepancies and special behavior noticed during
transients that diversify the operation from steady-state conditions. Wherever
possible, we provide experimental results to support our analysis. There are a few
points, however, where this was not feasible due to lack of relevant experimental
work (e.g., transient operation when the turbocharger compressor experiences
surge or crankshaft transient torsional deformation).
At this point, we would like to express our thanks to the various publishers and
companies, who have granted permission to reproduce figures and photos from
their publications. In particular, the assistance of Messrs Jörg Albrecht of MAN
Diesel SE, Elmar Gasse of Daimler AG, Chris Nickolaus of Cambustion Ltd, John
Zambelis of Isuzu Motors Greece, Martin Stenbäck of Lysholm Technologies AB,
Günther Krämer of BorgWarner Turbo Systems and Masayasu Kondo of
Mitsubishi Heavy Industries Europe Ltd is greatly appreciated.
Finally, we would like to thank our families, and our colleagues and students at
the National Technical University of Athens for their continuous support. Great
thanks are due to the editorial staff at Springer London; their editorial and technical
assistance has helped us enormously during the preparation of the book, and is thus
deeply appreciated.

Contents

Notation …………………………………………………………………………………………………..xv
1 Transient Operation Fundamentals………………………………………………………..1
1.1 Introduction ………………………………………………………………………………………1
1.2 Typical Transient Operation Cases……………………………………………………….7
1.2.1 Load Increase (Acceptance) Transient Event………………………………….8
1.2.2 Speed Increase (Acceleration) Transient Event …………………………….17
References ……………………………………………………………………………………………22
2 Thermodynamic Aspects of Transient Operation ………………………………….23
2.1 Turbocharger Lag and Transient Torque Pattern…………………………………..24
2.2 Fuel Injection…………………………………………………………………………………..38
2.2.1 Mechanical Fuel Injection…………………………………………………………38
2.2.2 Fuel Limiter…………………………………………………………………………….43
2.3 In-cylinder Processes ………………………………………………………………………..47
2.3.1 Heat Transfer …………………………………………………………………………..47
2.3.2 Combustion……………………………………………………………………………..51
2.4 Variable Geometry Turbine ……………………………………………………………….59
2.5 Exhaust Gas Recirculation…………………………………………………………………67
References ……………………………………………………………………………………………72
3 Dynamics …………………………………………………………………………………………….75
3.1 Engine Dynamics……………………………………………………………………………..75
3.1.1 Kinematics and Forces of the Slider-crank Mechanism………………….75
3.1.2 Crankshaft Torque Balance………………………………………………………..82
3.1.3 Mass Moments of Inertia …………………………………………………………..84
3.2 Governor…………………………………………………………………………………………85
3.2.1 Governor Fundamentals…………………………………………………………….85
3.2.2 Governor Equations ………………………………………………………………….90
3.3 Friction …………………………………………………………………………………………..94
3.3.1 Friction Fundamentals……………………………………………………………….94
3.3.2 Development of Friction Torque during Transients……………………….97
3.4 Crankshaft Torsional Deformation ……………………………………………………101
3.5 Introduction to Vehicle Dynamics…………………………………………………….105
3.5.1 Simplified Analysis…………………………………………………………………106
3.5.2 Detailed Vehicle Dynamics Study …………………………………………….110
References ………………………………………………………………………………………….113
4 Experimental Measurements………………………………………………………………115
4.1 Introduction: Steady-state Test Bed Review……………………………………….115
4.2 Transient Experimental Test Bed………………………………………………………117
4.2.1 Dynamometers ……………………………………………………………………….120
4.2.2 Instantaneous Measurement of Exhaust Gas and Particulate Matter 124
4.2.3 Heat Release Analysis of Transient Pressure Data ………………………135
References ………………………………………………………………………………………….138
5 Emissions…………………………………………………………………………………………..141
5.1 Particulate Matter and Smoke…………………………………………………………..141
5.2 Nitrogen Oxides……………………………………………………………………………..155
5.3 Hydrocarbons…………………………………………………………………………………161
5.4 Carbon Monoxide …………………………………………………………………………..164
5.5 Non-regulated Emissions and Odor …………………………………………………..165
5.6 Biodiesel ……………………………………………………………………………………….168
5.7 Combustion Noise ………………………………………………………………………….173
References ………………………………………………………………………………………….178
6 Methods of Improving Transient Response …………………………………………181
6.1 Introduction …………………………………………………………………………………..181
6.2 Type and Features of Applied Load, and the Effect of Various Dynamic
and Thermodynamic Parameters ………………………………………………………184
6.3 Air-injection…………………………………………………………………………………..189
6.4 Turbocharger Configuration …………………………………………………………….193
6.4.1 Turbocharger Mass Moment of Inertia ………………………………………194
6.4.2 Combined Supercharging…………………………………………………………199
6.4.3 Two-stage Turbocharging ………………………………………………………..202
6.4.4 Variable Geometry Turbine ……………………………………………………..206
6.4.5 Electrically Assisted Turbocharging ………………………………………….209
6.4.6 Sequential Turbocharging ………………………………………………………..215
6.5 Engine Configuration………………………………………………………………………217
6.5.1 Fuel Injection Control ……………………………………………………………..218
6.5.2 Valve Configuration………………………………………………………………..220
6.5.3 Manifolds Configuration………………………………………………………….223
6.5.4 Hybrid-electric Engine and Vehicle Operation……………………………225
References ………………………………………………………………………………………….236
7 Special Cases of Transient Operation………………………………………………….239
7.1 Cold Starting………………………………………………………………………………….239
7.1.1 Introduction……………………………………………………………………………239
7.1.2 Combustion Instability…………………………………………………………….241
7.1.3 Dynamics and Friction Development…………………………………………248
7.1.4 Exhaust Emissions ………………………………………………………………….250
7.2 Compressor Surge…………………………………………………………………………..254
7.2.1 Surge Fundamentals………………………………………………………………..254
7.2.2 Compressor Surge during Diesel Engine Transient Operation ………255
7.3 Low-heat Rejection Operation………………………………………………………….261
7.3.1 Load or Speed Increase Transients ……………………………………………262
7.3.2 Short Term Temperature Oscillations………………………………………..266
References ………………………………………………………………………………………….274
8 Second-law Analysis …………………………………………………………………………..277
8.1 Introduction …………………………………………………………………………………..277
8.2 Basic Concepts of Availability …………………………………………………………278
8.2.1 Availability of a System…………………………………………………………..278
8.2.2 Dead State ……………………………………………………………………………..279
8.2.3 General Availability Balance Equation………………………………………280
8.2.4 Fuel Availability …………………………………………………………………….281
8.3 Application of Exergy Balance to the Diesel Engine……………………………282
8.3.1 Engine Cylinder Exergy Balance ………………………………………………282
8.3.2 In-cylinder Irreversibilities ………………………………………………………284
8.3.3 Exergy Balance of the Engine Sub-systems………………………………..286
8.3.4 Second law or Exergy or Exergetic Efficiency ……………………………288
8.4 Exergy Balance Application to Steady-state Operation………………………..290
8.5 Exergy Balance Application to Transient Operation ……………………………293
References ………………………………………………………………………………………….303
9 Modeling……………………………………………………………………………………………305
9.1 Introduction …………………………………………………………………………………..305
9.2 Quasi-linear or Mean Value Approach ………………………………………………309
9.2.1 Engine Output ………………………………………………………………………..309
9.2.2 Exhaust Gas Temperature ………………………………………………………..310
9.2.3 Engine Air-flow ……………………………………………………………………..311
9.2.4 Transient Discrepancies …………………………………………………………..312
9.3 Filling and Emptying Approach ……………………………………………………….313
9.3.1 Thermodynamics Fundamentals ……………………………………………….314
9.3.2 In-cylinder Calculations…………………………………………………………..318
9.4 Manifolds………………………………………………………………………………………334
9.5 Multi-cylinder Engine Transient Operation………………………………………..336
9.6 Turbocharger …………………………………………………………………………………337
9.7 Friction …………………………………………………………………………………………342
9.7.1 Mean fmep Method…………………………………………………………………342
9.7.2 Rezeka–Henein Model…………………………………………………………….343
9.7.3 Account for Transient Discrepancies …………………………………………346
9.8 Fuel Injection…………………………………………………………………………………346
9.9 Mechanical Governor ……………………………………………………………………..348
9.10 Crankshaft Torque Balance ……………………………………………………………349
9.11 Exhaust Emissions ………………………………………………………………………..351
9.11.1 Global Approximations………………………………………………………..351
9.11.2 Nitric Oxide Formation Model………………………………………………352
9.11.3 Soot Formation Model …………………………………………………………352
9.12 Solution of Equations ……………………………………………………………………353
9.13 Sensitivity Analysis ………………………………………………………………………356
References ………………………………………………………………………………………….357
Appendix A – Exhaust Emission Regulations and Transient Cycles ………….361
A.1 Introduction…………………………………………………………………………………..361
A.2 European Union (EU) …………………………………………………………………….362
A.2.1 Emission Standards ……………………………………………………………….362
A.2.2 Transient Cycles……………………………………………………………………365
A.3 United States of America ………………………………………………………………..368
A.3.1 Emission Standards ……………………………………………………………….368
A.3.2 Transient Cycles……………………………………………………………………371
A.4 Japan ……………………………………………………………………………………………375
A.4.1 Emission Standards ……………………………………………………………….375
A.4.2 Transient Cycles……………………………………………………………………377
A.5 Overall: Comparative Data ……………………………………………………………..379
A.6 Worldwide Heavy-duty Transient Cycle …………………………………………..381
References ………………………………………………………………………………………….382
Appendix B – Fundamentals of Control Theory……………………………………….383
Index ……………………………………………………………………………………………………..387