Mixture Formation in Spark-Ignition Engines

H. P. Lenz in collaboration with W. B6hme, H. Duelli, G. Fraidl, H. Friedl, B. Geringer, P. Kohoutek, G. Pachta, E. Pucher, and G. Smetana

~ Springer-Verlag ~WienGmbH

Society of Automotive Engineers, Inc. Warrendale, P A

Univ.-Prof. Dipl.-Ing. Dr. sc. techn. Hans Peter Lenz Institute for Internal Combustion Engines and Automotive Engineering Technical University of Vienna, Austria

All rights are reserved, whether the whole or part of the material is concerned, specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks.

© 1992 Springer-Verlag Wien Originally published by Springer-Verlag/Wien in 1992 Softcover reprint of the hardcover 1st edition 1992

With 352 Figures

ISBN 978-1-56091-188-3 ISBN 978-1-4899-2762-0 (eBook) DOI 10.1007/978-1-4899-2762-0

Printed on acid-free paper

Preface

Twentyfour years have gone by since the publication of K. Lohner and H. Muller's comprehen­sive work "Gemischbildung und Verbrennung im Ottomotor" in 1967 [1.1]'

Naturally, the field of mixture formation and combustion in the spark-ignition engine has wit­nessed great technological advances and many new findings in the intervening years, so that the time seemed ripe for presenting a summary of recent research and developments. There­fore, I gladly took up the suggestion of the editors of this series of books, Professor Dr. H. List and Professor Dr. A. Pischinger, to write a book summarizing the present state of the art.

A center of activity of the Institute of Internal-Combustion Engines and Automotive Engineering at the Vienna Technical University, which I am heading, is the field of mixture formation - there­fore, many new results that have been achieved in this area in collaboration with the respective industry have been included in this volume.

The basic principles of combustion are discussed only to that extent which seemect necessary for an understanding of the effects of mixture formation.

The focal point of this volume is the mixture formation in spark-ignition engines, covering both the theory and actual design of the mixture formation units and appropriate intake manifolds. Also, the related measurement technology is explained in this work.

The intention of this book is to provide the engineer who is either engaged in scientific research or active in industry, as well as the student who wishes to deepen his knowledge in this field, with a survey of the present state of research and state of the art.

It should be pointed out that, after more than a hundred years' development in the field of en­gine design, intensive research work is being done worldwide, today more than ever, and great technological progress has been achieved. Therefore, the total of approximately 400 quoted direct sources of literature represent only a portion of the entire literature available.

I n view of the complexity of the subject, numerous experts have contributed to this volume, espe­cially former arid present staff members. I wish to take this opportunity to express my gratitude for elaboration of individual sections to: Dipl.-Ing. Dr. Walter Bohme, Dipl.-Ing. Dr. Heinz Duelli, Dipl.-Ing. Dr. Gunter Fraidl, Dipl.-Ing. Dr. Hubert Friedl, Dipl.-Ing. Dr. Bernhard Geringer, Dipl.­Ing. Dr. Georg Pachta, Dipl.-Ing. Dr. Ernst Pucher, and Dipl.-Ing. Dr. Gunter Smetana. I thank Professor Dr. Hellmuth Schindlbauer for his revision of the chapter "Fuel".

VI Preface

I also express deep appreciation for the great support and courtesy shown by the following pub­lishers and enterprises in permitting me to quote from copyright material including some illustra­tions:

Society of Automotive Engineers, Inc., Warrendale, Verlag des Vereins Deutscher Ingenieure, Dusseldorf, Adam Opel AG, ROsselsheim, AUDI AG, Ingolstadt, BMW AG, Munich, Dr. Ing. h.c. F. Porsche AG, Stuttgart, Fritz-Hintermayer GmbH., Nuremberg, Mercedes-Benz AG, Stuttgart, Pierburg GmbH., Neuss, R. Bosch GmbH., Stuttgart, Volkswagen AG, Wolfsburg

This book was originally published for the German-speaking public. In view of the vivid interest in this volume, I took up the suggestion that it should be translated for the English-speaking world. Most of the symbols and abbreviations used in illustrations, equations, and charts of the German edition have been retained in the English translation. Explanations are given in the corre­sponding indices.

Grateful acknowledgement is expressed to Mrs. Hedwig Riegler, assisted by Mag. Gertrude Maurer and Mag. Christine Hetzendorfer, for translating the book into English.

A special thanks goes to Mr. Ronald W. Bell, AC Rochester Austria, Vienna, who spared some of his valuable time for revision of the English manuscript.

The author is indebted to Dipl.-Ing. Dr. Ernst Pucher for editing and directing the translation pro­ject.

Dipl.-Ing. Peter Kohoutek deserves special mention for managing the layout and graphical pre­sentations.

Vienna, October 1991 o. Univ. Professor Dr. sc. techno Dipl.-Ing. Hans Peter Lenz

Contents

Symbols, Abbreviations, and Subscripts XIII

1. Basic Principles of Combustion 1

1.1 General .............. .

1.2 Determination of the Heating Value ............................ 2

1.3 Engine Cycle Fundamentals . . . . . . . . . . . . . .

1.3.1 Ideal Cycles and Simulation Cycles .... 1.3.2 The Carnot Cycle (Ideal Cycle) . . . . . . . 1.3.3 The Constant-Volume Cycle (Ideal Cycle) 1.3.4 The Constant-Pressure Cycle (Ideal Cycle) 1.3.5 The Limited-Pressure (Seiliger) Cycle (Ideal Cycle) 1.3.6 The Vibe Function . . . . . . . . . . . . . 1.3.7 Dissociation ............... . 1.3.8 Process Simulation and Computation ..

1.4 Details of the Combustion Process in Spark-Ignition Engines 1.4.1 Preflame Reactions ................ . 1.4.2 Preignition . . 1.4.3 Ignition 1.4.4 Ignition Delay . . . . . . . . . . .

1.4.5 Combustion Process and Charge Motion 1.4.6 Combustion Knock . . . . . . 1.4.7 Working Cycle . . . . . . 1.4.8 Efficiency

2. Basic Principles of Mixture Formation

2.1 Air ..

3 3 4 5 5 6 7

9 9

10 10 10 11 13 14 27 29 33

38

. ...... 38

2.2 Fuels ................................ 43

VIII

2.2.1 Requirements on Fuels .......... .

2.2.2 Composition and Structure of Fuels ... . 2.2.2.1 General ................ .

2.2.2.2 Pure Hydrocarbons . . . . . . . . . . . . . . .

2.2.2.2.1 Chainlike (Aliphatic) Hydrocarbons

2.2.2.2.2 Ring-Type (Cyclic) Hydrocarbons

2.2.2.3 Oxygenized Hydrocarbons . . . . . . . .

2.2.2.3.1 Alcohols (Alkanols) ....... .

2.2.2.3.2 Ethers ................ .

2.2.2.4 Fuel Additives . . . . . . . . . . . . . . . . .

2.2.3 Properties and Technical Characteristics of Fuels

2.2.3.1 Spark-Ignition-Engine Fuels (Gasoline) .....

2.2.3.2 Permanent Gas ........... .

2.2.3.3 Liquified Petroleum Gas ...... .

2.3 Stoichiometric Mixture Ratio; Relative Air/Fuel Ratio Lambda

2.4 Fuel Management ................ .

2.4.1 Mixture Quantity . . . . . . . . . . 2.4.2 Mixture Composition

2.5 Mixture Preparation . . . . .

2.5.1 Fuel Atomization . . .

2.5.1.1 Airless Atomization .... .

2.5.1.2 Air-Assisted Atomization ... . 2.5.2 Fuel Vaporization ......... .

2.6 Mixture Flow and Distribution ......... .

2.6.1 Mixture Flow and Distribution in Single-Point Mixture Formation Systems . .

2.6.1.1 General Description . . . . . . . . . . . 2.6.1.2 Air and Fuel Vapor (Gas) ....... .

2.6.1.3 Fuel Droplets ........ . . . . . 2.6.1.4 Wall Film . . . . . . . . . . . . . . . .

2.6.2 Mixture Flow and Distribution in a

Multi-Point Mixture Formation System ............... .

3. Laboratory Diagnostics

3.1 Measurement of Air Mass Flow and Fuel Mass Flow

3.1.1 Air Mass Flow Measurements

Contents

43 44 44 45 45

48

50

50 51

52

54 54

60 61

64

66 66 69

75

78

80 85 88

94

94

94 95

96 · 101

. . . . . · 107

112

· 112

· 112

Contents

3.1.2 Fuel Mass Flow Measurements

3.2 Determination of the Air-Fuel Ratio (Lambda)

3.2.1 General .............. .

3.2.2 Accuracy of Different Air-Fuel Ratio Measurement Techniques

3.2.2.1 Atom Balance Procedure . . . . . . . . . . . . . . . . . .

3.2.2.2 Single-Constituent Air-Fuel Ratio Computation ..... . 3.2.3 Comparison of Air-Fuel Ratio Measurement Procedures Based

on Exhaust Gas Analysis .............. .

3.2.4 Transient Air-Fuel Ratio Measurement ....... .

3.2.5 Air-Fuel Ratio Determination in Two-Stroke Engines

3.3 Wall Film Measurements .

3.4 Droplet Sizing .......... .

3.4.1 Droplet Sizing Techniques ..

3.4.1.1 Photographic Techniques

3.4.1.2 Absorption Technique

3.4.1.3 Scattered-Light Method . .

3.4.2 Theoretical Principles of Scattered-Light Techniques 3.4.3 Arrangement and Apparatus of the Scattered-Light Method

3.4.4 Sources of Error and Measuring Accuracy of the

Scattered-Light Method . . . . . . . . . . . . . . .

3.4.4.1 Double Refraction . . . . . . . . . . . . . . . . 3.4.4.2 Nonhomogeneities in the Measurement Beam

3.4.4.3 Evaluation Method ............ .

3.4.4.4 Other Influences on Measurement Results .. .

3.4.4.5 Measurement Accuracy . . . . . . . . . . . . .

3.4.5 Options for Presenting Steady-State Droplet Size Distributions

3.4.6 Presentation of Transient Droplet Size Distributions . . . . . .

3.5 Measurement of Injector Spray Characteristics . . . . . .

4. Types of Mixture Formation Systems

4.1 Single-Point Mixture Formation Systems

4.1.1 The Carburetor ....... .

4.1.1.1 Basic Equations . . . . . . . .

4.1.1.2 Basic Carburetor Systems ..

4.1.1.2.1 Air Funnel, Throttle Valve .

4.1.1.2.2 Devices to Control the Fuel Level

4.1.1.2.3 The Main Nozzle System ....

IX

· 113

· 114

· 114

· 116

· 116

· 117

· 119

· 120

· 120

· 121

· 122

· 122

· 123 · 124

· 124

· 125 · 127

· 129

· 129

· 129

· 131

· 132

· 132

· 133

· 135

· 137

139

· 139

· 140 · 141

· 144 · 144

· 156

· 160

x 4.1.1.2.4 The Idling System ........ .

4.1.1.2.5 The Bypass System . . . . . . . .

4.1.1.2.6 The Starting and Warm-up System 4.1.1.2.7 Accelerating Pumps . . . . . . . .

4.1.1.2.8 Devices to Control Fuel Enrichment 4.1.1.2.9 Auxiliary Mixture Systems

4.1.1.2.10 Overrun Operation . . . .

4.1.1.2.11 Atmospheric Corrections 4.1.1.2.12 Icing ....

4.1.1.2.13 Vapor Locks . . . . . . .

4.1.1.3 Carburetor Types . . . . . . . .

4.1.1.4 Constant-Depression Carburetors

4.1.1.5 Carburetors with Electronic or Closed-Loop Control 4.1.1.6 Carburetor Design Examples . . . . . . . . . . . .

4.1.1.6.1 Pierburg Compound Carburetor 2E 4.1.1.6.2 Pierburg Double Compound Carburetor 4A 1 4.1.1.6.3 Carburetors for Small Engines, Bing Carburetors

4.1.1.6.4 Pierburg Electronic Carburetor

4.1.2 Single-Point Injection ..... .

4.1.2.1 Bosch Mono-Jetronic . . . . . . .

4.1.2.2 Nissan Single-Point Injection ... 4.1.2.3 Opel Multec Central Injection Unit

4.1.2.4 Honda Dual-Point Injection ....

4.1.3 LPG Mixer Units . . . . . . . . . . . . 4.1.4 The Geometric Design of Mixture Formation Systems and Its Effect on

Mixture Distribution .

4.1.4.1 General ...... . 4.1.4.2 The Throttle Valve . .

4.1.4.3 The Mixing Chamber

4.1.4.4 Intake Air Route ...

4.1.4.5 Injection Timing and Its Effect on Mixture Distribution

4.2 Multi-Point Mixture Formation Systems . . . .

4.2.1 Individual-Cylinder Injection Systems

4.2.1.1 A History of Fuel Injection Systems

4.2.2 Electronic Intermittent Injection Systems.

4.2.2.1 Bosch L-Jetronic .......... .

4.2.2.2 Bosch LH-Jetronic ......... .

4.2.3 Continuous Mechanical/Electronic Injection Systems

4.2.3.1 Bosch K-Jetronic .

4.2.3.2 Bosch KE-Jetronic

4.3 Solenoid Injectors ........ .

4.3.1 Basic Function and Structure

Contents

· 165

· 166 · 171 .174 .176 · 177

· 178

· 178

· 184

· 185 · 186 · 189

· 191

· 194 · 194 .200 .204 .208

· 211

· 212

· 215 · 218 .222 .223

.229

.229

.230

.232

.236

.237

.240

.240

.240

.252

.252

.263

.264

.264

· 271

.278

.278

Contents

4.3.2 A Comparison of Injector Designs ...

4.3.2.1 General ......... . 4.3.2.2 Pintle -Type Injectors .. .

4.3.2.3 Single-Hole-Type Injectors 4.3.2.4 Multi-Hole-Type Injectors .

4.3.3 Key Parameters of Solenoid-Operated Injectors

4.4 Air Mass Flow Measurement

4.4.1 Air Flow Sensors 4.4.2 Vortex Flowmeters

4.4.3 Thermal Sensors .

4.4.3.1 Hot-Wire Air Mass Flowmeter .

4.4.3.2 Hot-Film Air Mass Flowmeter .

4.5 Combined Mixture Formation /Ignition/ Engine Management Systems

4.6 Mixture Formation Requirements of Multivalve Engines .

4.6.1 Differences Between Two- and Multivalve Engines

with Regard to Mixture Formation ...... .

4.6.2 Effects on Mixture Formation and Optimization ..

4.7 A Comparative Evaluation of Mixture Formation Systems

5. Intake Manifold Design

5.1 Intake Manifolds for Single-Point Mixture Formation Systems

5.1.1 Intake Manifold Requirements 5.1.2 Design Principles ........ 5.1.3 Basic Intake Manifold Geometry

5.1.3.1 Type of Induction System ..

5.1.3.2 Type of I ntake Manifold Geometry

5.1.4 Intake Manifold Heating ..

5.1.5 Intake Manifold Volume .. 5.1.5.1 Runner Cross-Section

5.1.5.2 Length of Runners

5.1.5.3 Distributor Volume .. 5.1.6 Mixture Deflections and Branchings 5.1.7 Geometry of Pipe Cross Sections 5.1.8 Distributor Geometry and Integral Distributor Parts

5.1.9 Inclination of the Intake Manifold

5.1.10 Connection Bores ... 5.1.11 Intake Manifold Material

.......

XI

.280

.280

.282

.282

.282

.283

.286

.286

.287

.287

.288

.290

.293

.297

.297

.299

.304

307

.307

.307

.307

· 310

· 310

· 312 · 316 .324

.324

.327

.328

.328

.330

· 331 .334

.334

.334

XII

5.1.12 Surface Roughness . . . . . . . . . . . . . . . .

5.1.13 Intermediate Flange Between Intake

Manifold and Mixture Formation System . . . . .

5.2 Intake Manifold Design for Multi-Point Mixture Formation Systems .

5.2.1 General .................. .

5.2.2 Tuned-Intake Tube Charging ....... . . . . . . . . . . .

5.2.3 Ram Pipe Supercharging . . . . . . . . . . . . . . . . . . . .

5.2.4 Unconventional Induction Systems Without Variable Dimensions .

5.2.5 Variable Induction Systems . . . . . . . . . . . . . . . . . . . .

5.2.6 Computation of Intake Manifolds for Multi-Point Injection ..... .

6. Special Mixture Formation Varieties

6.1 Special Single-Point Mixture Formation Varieties

6.2 Special Multi-Point Mixture Formation Varieties .

7. Bibliography

Subject Index

Contents

· .335

· .336

· .338

· .338 · .. 338

· .. 343

· .349 · .353

· .358

360

· .. 360

· .. 364

367

392

Symbols, Abbreviations, and Subscripts

Symbols

a,b [m) Distance A [m2) Area (various dimensions) b [m.s-2) Acceleration b [g.kW1.h-1) Specific fuel consumption B [l.h-1) Fuel consumption c [m.s-1) Sonic speed Cy,cp [J.kg-1K 1] Specific heat capacity with v = const. or p = const. dx/d<p [oK(1) Energy conversion rate D,d [mm) Diameter D32 [lLm) Sauter diameter D32 [lLm) Sauter mean diameter E(x)/Emax [ -) Normalized scattered light energy E [J) Energy f [-) Factor f [Hz) Frequency, number of ignition sparks f [mm) Focal length, lens focal length fSE [mm2.kW1) Specific individual-pipe cross-section factor F [%] Film-like fuel fraction F [N] Force FR [N.kg-1) Specific friction (related to p.A.dx) g [m.s-2] Gravitational acceleration h [m) Height (h/c) Mass [ -) Hydrogen/carbon mass ratio H [kJ.m-3] Heating value HC [g) Total emission of unburned hydrocarbons Ho [kJ.kg-1] Specific heating power (or high heating value) HG [kJ.m-3) Mixture heating value Hu [kJ.kg-1) Specific heating value (or low heating value) of liquid fuel Hu [kJ.m-3] Specific heating value (or low heating value) of gaseous fuel iHA [ -] Transmission of driven axle I (x)/Imax [-) Normalized scattered light intensity IH [A) Heating current ksld [ -] Referenced pipe roughness K [-) Constant L, I [m) Length m [kg) Mass

XIV Symbols, Abbreviations, and Subscripts

m [kg.s-1] Mass flow rate, throughput

m [mm3.(msr1] Steady flow

m [-] Vibe factor

mF [%] Fuel film deposit M [ -] Mixture ratio

Md [N.m] Engine torque

n [ -] Number n [min-1] Torque

N [kW] Power, engine power

NOx [g] Total emission of nitric oxides

(o/c) Mass [-] Oxygen/carbon mass ratio

Oh [-] Ohnesorge number

p [N.m-2] Pressure

ps [N.m-2] Manifold vacuum (various dimensions)

q [mm3] Injected fuel volume per cycle

qA [J.kg-1] Dissipated specific heat

qs [J.kg-1] Added specific heat

Q [J] Heat

QA [%] Squish area portion

r [m] Radius

r [mm] Measurement radius in focal plane

R [0] Impedance

R [J.kg-1.1(1 ] Specific gas constant

Re [ -] Reynolds number

S [J.I(1] Entropy

s [J.kg-1.1(1] Specific entropy

s [m] Stroke, travel

t [s] Time

t [s] Pulsation period

T [oK,°C] Temperature

Ti [ms] Pulse length

Ti [ms] Pulse timing

Tm [ms] Extension of pulse length by correction

Tp [ms] Basic injection time

Tt [ms] Droplet travel time

Tu [ms] Extension of pulse length by voltage compensation

Tv [ms] Time delay

U [V] Voltage

U"- [mY] Probe voltage

Uv [V] Control voltage

Uv [V] Valve control voltage

v [m.s-1] Velocity

v [m3.kg-1] Specific volume

V [cm3] Volume (various dimensions)

Symbols, Abbreviations, and Subscripts XV

V [mm3.ms-1] Steady flow volume

V [m3.h-1] Flow rate, throughput

Vc [m3] Compression volume VF [m.s-1] Mean fuel film velocity

VH [dm3] Displacement volume (various dimensions) V [%] Coefficient of variation

We [kJ.dm-3] Specific effective work We [-] Weber number

x [m] Location coordinate

x [-] Water or fuel content of the air

x [-] Normalized measurement radius y [m] Location coordinate

a [-] Flow index a [0] Angle

az [oKW] Ignition angle

& [lJ..m] Wall film thickness & [0] Angle, bending angle

aK [%] Deviation of individual-cylinder air-fuel equivalence ratio from the

AOT [m2]

ap [mbar]

(aptl) R,zp [mbar.m-1]

apR [N.m-2]

E [-] E [ -] <P [-]

'Y [kg.m-3]

1') [ -] 1')0 [-] 1') [Pa.s]

q> [oCA]

q> [-] q> [oCA]

q>B lOCAl

q>tq>B [-] K [ -] K [ -] x [-] x, [-] X, [mm]

A.a [ -] x'R [-]

IJ.. [-] v [m2.s-1]

mean equivalence ratio of all cylinders

Surface enlargement due to jet breakup

Pressure loss (various dimensions) Referenced frictional pressure loss

Frictional pressure loss

Engine compression ratio

Width/length ratio Pulsation parameter

Density

Efficiency

Nozzle efficiency

Dynamic viscosity (various dimensions)

Temporal phase of energy conversion Ratio of volume rise Crank angle

Burning time, combustion time

Normalized crank position (burning time) Specific heat ratio

Air-fuel equivalence ratio

Fraction of fuel energy released (burning function)

Relative air-fuel ratio

Wavelength, light wavelength

Air consumption

Pipe friction coefficient

Constriction index

Kinematic viscosity

XVI

E> p

cr ,.

[0] [kg.m-3]

[N.m-2]

[N.m-2]

[-I [ -] [ -] [-I [ -]

Scattering angle Density Surface tension Shear stress

Symbols, Abbreviations, and Subscripts

Oxygen/carbon atomic ratio in the fuel Ratio of pressure rise Flow function Hydrogen/carbon atomic ratio in the fuel Drag coefficient

Abbreviations and Subscripts

0 Standard condition B Fuel 0 Reference condition (ambient B Added

condition) B Vessel 0 At rest BA Acceleration enrichment A Buoyancy BDC Bottom dead center A Surge tank C Compression A Exhaust CA Crank angle A Exhaust valve CFR Cooperative Fuel Research A Dissipated Committee, USA A Intake const Constant abs, Abs Absolute CVCC Compound Vortex Controlled atm Atmospheric Combustion ABS Anti-blocking system CN Cetane number AEGS Electronic gear controller Cyl Cylinder NF Air/fuel 0 Vapor AFI Air-fuel injection system DFR Dynamic flow range AS Exhaust valve closes DKA Throttle valve switch ACS Anti-blocking system with stability DIN German Institute for Standar-

check dization ASTM American Standard Test Method OK Throttle valve AVL Ges. fOr Verbrennungskraft- DME Digital engine control electronics

maschinen u. MeBtechnik m.b.H., OS Saturated vapor Prof. Dr. Dr. h.c. Hans List DSM Dividing control oscillator

* Critical condition DVG Deutsche Vergaser-Gesellschaft (x) Normalized measurement radius (German Carburetor Society)

Symbols, Abbreviations, and Subscripts XVII

e,eff Effective LL Idle

E Inlet LPG Liquified petroleum gas

E Inlet valve LT Air funnel

ECE Economic Commission for Europe M Mixing chamber

ECU Electronic control unit M Mean value

EMK Electromotive force M Engine

EML Electronic engine management m Mass flow

controller m Mean

EO Inlet valve opens max Maximum

ES I nlet valve closes min Minimum

ES Output stage MON Motor octane number ETBE Ethyl tertiary butyl ether MSR Engine overrun control

EV Injector MTBE Methyl tertiary butyl ether

f Humid MTL T etramethyllead

Fig Figure NA Post-start enrichment

FI Liquid NTC Negative temperature coefficient FON Front octane number OH Hydroxyl group FTP Federal Test Procedure ONORM Austrian Standard

G Mixture formation system opt Optimum

G Mixture OT(TDC)Top dead center

G Gas ON Octane number ges Total PCI Pre-chamber-injection

GS Saturated mixture PLU Pierburg Aviation Union H Hot wire proz In percent HA Rear axle PTC Positive temperature coefficient HLM Hot-wire air mass flowmeter R Impedance

HSP Hot spot R Friction Indicated R Resonance Internal red Reduced Pulse rei Relative

I Current RON Research octane number ISA International Standard Atmosphere S, s Intake manifold inst Transient SA Voltage increase for starting IS Heating current SAS Overrun fuel cut -off

IVK Institute for Internal-Combustion SCS Stratified charge system (Porsche)

Engines and AutomotiveE spez Specific ngineering SON Street octane number

IC Integrated circuit stat Steady-state

K Fuel sto Stoichiometric k Coolant SU Adder stage KD Fuel nozzle T Droplet

Liters t Dry L Air Tab Table LK Air compensation TBI Throttle body injection

XVIII Symbols, Abbreviations, and Subscripts

TOC Top dead center VL Full load th Thermal VZ Preliminary diffuser TL Part-load W Wall TOP Thermodynamically optimized WA Warm-up enrichment

Porsche engine WO Water vapor O.OT Overlap top dead center ZOT Ignition top dead center UT(BOC)Bottom dead center zu Added, supplied VK Full-load correction Z,Zyl Cylinder VO Initial throttle valve ZZP Ignition point