Mixture formation in internal combustion engine.pdf

Carsten Baumgarten

Mixture Formation in

Internal Combustion

Engines

With 1 0 Figures

and 9 Tables

Dr.-Ing.

arsten

Baumgarten,

MTU Friedrichshafen GmbH

Maybachplat 1

88045 Friedrichshafen

Germany

Series Editors

Prof. Dr.-Ing. Dieter Mewes

Universität Hannover

Institut für Verfahrenstechnik

Prof. em. Dr.-Ing. E.h. Franz Mayinger

Technische Universität München

Lehrstuhl für Thermodynamik

Boltzmannstr. 15

85748 Garching, Germany

Callinstr. 36

30167 Hannover, Germany

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1860-4846

3-540-

3 0350

- Springer-Verlag Berlin Heidelberg New York

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Preface

A systematic control of mixture formation with modern high-pressure injection

systems enables us to achieve considerable improvements of the combustion proc-

ess in terms of reduced fuel consumption and engine-out raw emissions. However,

because of the growing number of free parameters due to more flexible injection

systems, variable valve trains, the application of different combustion concepts

within different regions of the engine map, etc., the prediction of spray and mix-

ture formation becomes increasingly complex. For this reason, the optimization of

the in-cylinder processes using 3D computational fluid dynamics (CFD) becomes

increasingly important.

In these CFD codes, the detailed modeling of spray and mixture formation is a

prerequisite for the correct calculation of the subsequent processes like ignition,

combustion and formation of emissions. Although such simulation tools can be

viewed as standard tools today, the predictive quality of the sub-models is con-

stantly enhanced by a more accurate and detailed modeling of the relevant proc-

esses, and by the inclusion of new important mechanisms and effects that come

along with the development of new injection systems and have not been consid-

ered so far.

In this book the most widely used mathematical models for the simulation of

spray and mixture formation in 3D CFD calculations are described and discussed.

In order to give the reader an introduction into the complex processes, the book

starts with a description of the fundamental mechanisms and categories of fuel in-

jection, spray break-up, and mixture formation in internal combustion engines.

They are presented in a comprehensive way using data from experimental investi-

gations. Next, the basic equations needed for the simulation of mixture formation

processes are derived and discussed in order to give the reader the basic knowl-

edge needed to understand the theory and to follow the description of the detailed

sub-models presented in the following chapters. These chapters include the model-

ing of primary and secondary spray break-up, droplet drag, droplet collision, wall

impingement, and wall film formation, evaporation, ignition, etc. Different model-

ing approaches are compared and discussed with respect to the theory and

underlying assumptions, and examples are given in order to demonstrate the

capabilities of today’s simulation models as well as their shortcomings. Further

on, the influence of the computational grid on the numerical computation of spray

processes is discussed. The last chapter is about modern and future mixture

formation and combustion processes. It includes a discussion of the potentials and

future developments of high-pressure direct injection diesel, gasoline, and

homogeneous charge compression ignition engines.

VI Preface

This book may serve both as a graduate level textbook for combustion engi-

neering students and as a reference for professionals employed in the field of

combustion engine modeling.

The research necessary to write this book was carried out during my employ-

ment as a postdoctoral scientist at the Institute of Technical Combustion (ITV) at

the University of Hannover, Germany. The text was accepted in partial fulfillment

of the requirements for the postdoctoral Habilitation-degree by the Department of

Mechanical Engineering at the University of Hannover.

There are many people who helped me in various ways while I was working on

this book. First, I would like to thank Prof. Dr.-Ing. habil. Günter P. Merker, the

director of the Institute of Technical Combustion, for supporting my work in every

possible respect. Prof. Dr.-Ing. Ulrich Spicher, the director of the Institute of Re-

ciprocating Engines, University of Karlsruhe, and Prof. Dr.-Ing. habil. Dieter

Mewes, the director of the Institute of Process Engineering, University of Han-

nover, contributed to this work by their critical reviews and constructive com-

ments.

I would also like to thank my colleagues and friends at the University of Han-

nover who gave me both, information and helpful criticism, and who provided an

inspiring environment in which to carry out my work. Special thanks go to Mrs.

Christina Brauer for carrying out all the schematic illustrations and technical

drawings contained in this book.

Hannover, October 2005 Carsten Baumgarten

Contents

Preface.................................................……………..........……….…………….. V

Contents……………………………………………………..……………….... VII

Nomenclature………………………………………………………………..… XI

1 Introduction………………………………………………………………….... 1

1.1 Modeling of Spray and Mixture Formation Processes………………...…. 1

1.2 Future Demands…………………………………………………...……... 3

2 Fundamentals of Mixture Formation in Engines…………………………… 5

2.1 Basics………………………………………………………………....…... 5

2.1.1 Break-Up Regimes of Liquid Jets……………………………....…… 5

2.1.2 Break-Up Regimes of Liquid Drops………………………………… 8

2.1.3 Structure of Engine Sprays…………………………………...……. 10

2.1.4 Spray-Wall Interaction…………………………………………...... 29

2.2 Injection Systems and Nozzle Types……………………………...……. 32

2.2.1 Direct Injection Diesel Engines………………………………....…. 32

2.2.2 Gasoline Engines………………………………………………...… 38

References……………………………………………………………...….... 43

3 Basic Equations…………………………………………………………....… 47

3.1 Description of the Continuous Phase………………………………...…. 47

3.1.1 Eulerian Description and Material Derivate…………………...…... 47

3.1.2 Conservation Equations for One-Dimensional Flows………...…… 49

3.1.3 Conservation Equations for Multi-Dimensional Flows…………..... 54

3.1.4 Turbulent Flows………………………………………………....…. 66

3.1.5 Application to In-Cylinder Processes…………………………...…. 79

3.2 Description of the Disperse Phase……………………………………… 81

3.2.1 Spray Equation…………………………………………………….. 81

3.2.2 Monte-Carlo Method…………………………………………….… 82

3.2.3 Stochastic-Parcel Method…………………………………....…….. 82

3.2.4 Eulerian-Lagrangian Description…………………………..…...…. 83

References…………………………………………………………….....….. 83

4 Modeling Spray and Mixture Formation………………………...……... 85

4.1 Primary Break-Up……………………………………………….……… 85

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