Merker / Schwarz / Stiesch Simulating Combustion

Simulation of combustion and pollutant formation for engine-development
1. Auflage 2005
ISBN: 978-3-540-30626-9
Verlag: Springer Berlin Heidelberg
Format: PDF
Kopierschutz: 1 - PDF Watermark

E-Book, Englisch, 424 Seiten

The numerical simulation of combustion processes in internal combustion engines, including also the formation of pollutants, has become increasingly important in the recent years, and today the simulation of those processes has already become an indispensable tool when - veloping new combustion concepts. While pure thermodynamic models are well-established tools that are in use for the simulation of the transient behavior of complex systems for a long time, the phenomenological models have become more important in the recent years and have also been implemented in these simulation programs. In contrast to this, the thr- dimensional simulation of in-cylinder combustion, i. e. the detailed, integrated and continuous simulation of the process chain injection, mixture formation, ignition, heat release due to combustion and formation of pollutants, has been significantly improved, but there is still a number of challenging problems to solve, regarding for example the exact description of s- processes like the structure of turbulence during combustion as well as the appropriate choice of the numerical grid. While chapter 2 includes a short introduction of functionality and operating modes of internal combustion engines, the basics of kinetic reactions are presented in chapter 3. In chapter 4 the physical and chemical processes taking place in the combustion chamber are described. Ch- ter 5 is about phenomenological multi-zone models, and in chapter 6 the formation of poll- ants is described.

Professor Dr.-Ing. habil. Günter Peter Merker received is Dr.-Ing. for his thesis on Thermodynamics in Munich, where he received the venia legendi as well. Since 1994 he is Professor for Applied Thermodynamics at Hannover University, Faculty of Mechanical Engineering, and renown for his scientific work for major public and industrial research institutions.
Professor Dr.-Ing.habil Christian Schwarz studied Mechanical Engineering in Munich. Since 1997 Professor Schwarz is employed by BMW AG.
Dr.-Ing. habil Gunnar Stiesch studied Mechanical Engineering at Hannover University and University of Wisconsin-Madison. In the year 2000 he was research fellow at the Engine Research Center at the University of Wisconsin-Madison. Since 2003 Dr. Stiesch is a researcher for MTU Friedrichshafen GmbH.
Dr. rer. nat. Frank Otto studied Physics Heidelberg University, where he finished his PhD-Thesis 1991. Since 2002 Dr. Otto works as a Projectmanager for Daimler Chrysler AG.  

Autoren/Hrsg.

Merker, Günter P.

Schwarz, Christian

Stiesch, Gunnar

Otto, Frank

Inhaltsverzeichnis

1;Preface;6
2;Table of contents;7
3;Abbreviations;12
4;Symbols;13
5;Greek symbols;18
6;Operators;20
7;Indices;20
8;1 Introduction;25
8.1;1.1 Preface;25
8.2;1.2 Model-building;25
8.3;1.3 Simulation;26
9;2 Introduction into the functioning of internal combustion engines;29
9.1;2.1 Energy conversion;29
9.2;2.2 Reciprocating engines;30
9.2.1;2.2.1 The crankshaft drive;31
9.2.2;2.2.2 Gas and inertia forces;33
9.2.3;2.2.3 Procedure;35
9.3;2.3 Thermodynamics of the internal combustion engine;36
9.3.1;2.3.1 Foundations;36
9.3.2;2.3.2 Closed cycles;41
9.3.3;2.3.3 Open comparative processes;49
9.4;2.4 Characteristic qualities and characteristic values;52
9.5;2.5 Engine maps;55
9.5.1;2.5.1 Spark ignition engines;55
9.5.2;2.5.2 Diesel engines;57
9.6;2.6 Charging;59
9.6.1;2.6.1 Charging methods;59
9.6.2;2.6.2 Supercharging;61
9.6.3;2.6.3 Constant-pressure turbocharging;62
9.6.4;2.6.4 Pulse turbocharging;65
10;3 Foundations of reaction kinetics;68
10.1;3.1 Chemical equilibrium;68
10.2;3.2 Reaction kinetics;71
10.3;3.3 Partial equilibrium and quasi-steady-state;72
10.4;3.4 Fuels;74
10.4.1;3.4.1 Chemical structure;74
10.4.2;3.4.2 Physical and chemical properties;77
10.5;3.5 Oxidation of hydrocarbons;80
11;4 Engine combustion;84
11.1;4.1 Spark ignition engines;84
11.1.1;4.1.1 Mixture formation;84
11.1.2;4.1.2 Ignition;87
11.1.3;4.1.3 The combustion process;89
11.1.4;4.1.4 Abnormal combustion;93
11.1.5;4.1.5 Controlled autoignition;94
11.2;4.2 Diesel engines;96
11.2.1;4.2.1 Injection methods and systems;97
11.2.2;4.2.2 Mixture formation;104
11.2.3;4.2.3 Autoignition;105
11.2.4;4.2.4 Combustion;107
11.2.5;4.2.5 Homogeneous combustion;110
11.3;4.3 Pressure trace analysis;112
11.3.1;4.3.1 Determination of the heat release rate;112
11.3.2;4.3.2 Loss distribution;116
11.3.3;4.3.3 Comparison of various combustion processes;119
12;5 Phenomenological combustion models;122
12.1;5.1 Diesel engine combustion;122
12.1.1;5.1.1 Zero-dimensional heat release function;122
12.1.2;5.1.2 Stationary gas jet;123
12.1.3;5.1.3 Packet models;128
12.1.4;5.1.4 Time scale models;135
12.2;5.2 SI engine combustion;137
13;6 Pollutant formation;140
13.1;6.1 Exhaust gas composition;140
13.2;6.2 Carbon monoxide (CO);141
13.3;6.3 Unburned hydrocarbons (HC);142
13.3.1;6.3.1 Limited pollutant components;142
13.3.2;6.3.2 Non-limited pollutant components;146
13.4;6.4 Particulate matter emission in the diesel engine;151
13.4.1;6.4.1 Introduction;151
13.4.2;6.4.2 Polycyclic aromatic hydrocarbons (PAH);152
13.4.3;6.4.3 Soot development;153
13.4.4;6.4.4 Particle emission modeling;155
13.5;6.5 Nitrogen oxides;156
13.5.1;6.5.1 Thermal NO;157
13.5.2;6.5.2 Prompt NO;162
13.5.3;6.5.3 NO formed via N2O;164
13.5.4;6.5.4 Fuel nitrogen;164
14;7 Calculation of the real working process;165
14.1;7.1 Single-zone cylinder model;166
14.1.1;7.1.1 Fundamentals;166
14.1.2;7.1.2 Mechanical work;168
14.1.3;7.1.3 Determination of the mass flow through the valves / valve lift curves;168
14.1.4;7.1.4 Heat transfer in the cylinder;171
14.1.5;7.1.5 Heat transfer in the exhaust manifold;180
14.1.6;7.1.6 Wall temperature models;181
14.1.7;7.1.7 The heat release rate;184
14.1.8;7.1.8 Knocking combustion;198
14.1.9;7.1.9 Internal energy;202
14.2;7.2 The two-zone cylinder model;211
14.2.1;7.2.1 Modeling the high pressure range according to Hohlbaum;211
14.2.2;7.2.2 Modeling the high pressure phase according to Heider;214
14.2.3;7.2.3 Results of NOx calculation with two-zone models;217
14.2.4;7.2.4 Modeling the charge changing for a 2-stroke engine;219
14.3;7.3 Modeling the gas path;221
14.3.1;7.3.1 Modeling peripheral components;221
14.3.2;7.3.2 Model building;223
14.3.3;7.3.3 Integration methods;224
14.4;7.4 Gas dynamics;225
14.4.1;7.4.1 Basic equations of one-dimensional gas dynamics;225
14.4.2;7.4.2 Numerical solution methods;229
14.4.3;7.4.3 Boundary conditions;232
14.5;7.5 Charging;238
14.5.1;7.5.1 Flow compressor;238
14.5.2;7.5.2 The positive displacement charger;248
14.5.3;7.5.3 The flow turbine;249
14.5.4;7.5.4 Turbochargers;260
14.5.5;7.5.5 Charge air cooling;263
15;8 Total process analysis;269
15.1;8.1 General introduction;269
15.2;8.2 Thermal engine behavior;269
15.2.1;8.2.1 Basics;269
15.2.2;8.2.2 Modeling the pipeline system;270
15.2.3;8.2.3 The cooling cycle;272
15.2.4;8.2.4 The oil cycle;275
15.2.5;8.2.5 Physical properties of oil and coolant;280
15.3;8.3 Engine friction;281
15.3.1;8.3.1 Friction method for the warm engine;281
15.3.2;8.3.2 Friction method for the warm-up;282
15.4;8.4 Engine control;285
15.4.1;8.4.1 PID controller;285
15.4.2;8.4.2 Load control;285
15.4.3;8.4.3 Combustion control;286
15.4.4;8.4.4 Control of exhaust gas recirculation;286
15.4.5;8.4.5 Charger aggregate control;288
15.4.6;8.4.6 The driver controller;290
15.5;8.5 Representing the engine as a characteristic map;291
15.5.1;8.5.1 Procedure and boundary conditions;291
15.5.2;8.5.2 Reconstruction of the torque band;293
15.6;8.6 Stationary simulation results (parameter variations);296
15.6.1;8.6.1 Load variation in the throttled SI engine;297
15.6.2;8.6.2 Influence of ignition and combustion duration;298
15.6.3;8.6.3 Variation of the compression ratio, load, and peak pressure in the large diesel engine;300
15.6.4;8.6.4 Investigations of fully variable valve trains;301
15.6.5;8.6.5 Variation of the intake pipe length and the valve control times (SI engine, full load);303
15.6.6;8.6.6 Exhaust gas recirculation in the turbocharged diesel engine of a passenger car;303
15.6.7;8.6.7 Engine bypass in the large diesel engine;307
15.7;8.7 Transient simulation results;309
15.7.1;8.7.1 Power switching in the generator engine;309
15.7.2;8.7.2 Acceleration of a commercial vehicle from 0 to 80 km/h;311
15.7.3;8.7.3 Turbocharger intervention possibilities;313
15.7.4;8.7.4 Part load in the ECE test cycle;314
15.7.5;8.7.5 The warm-up phase in the ECE test cycle;316
15.7.6;8.7.6 Full load acceleration in the turbocharged SI engine;317
16;9 Fluid mechanical simulation;321
16.1;9.1 Three-dimensional flow fields;321
16.1.1;9.1.1 Basic fluid mechanical equations;321
16.1.2;9.1.2 Turbulence and turbulence models;327
16.1.3;9.1.3 Numerics;337
16.1.4;9.1.4 Computational meshes;344
16.1.5;9.1.5 Examples;345
16.2;9.2 Simulation of injection processes;350
16.2.1;9.2.1 Single-droplet processes;351
16.2.2;9.2.2 Spray statistics;355
16.2.3;9.2.3 Problems in the standard spray model;367
16.2.4;9.2.4 Solution approaches;371
16.3;9.3 Simulation of combustion;378
16.3.1;9.3.1 General procedure;378
16.3.2;9.3.2 Diesel combustion;381
16.3.3;9.3.3 The homogeneous SI engine (premixed combustion);389
16.3.4;9.3.4 The SI engine with stratified charge (partially premixed flames);404
17;Literature;406
18;Index;415

Leseproben

1 Introduction (p. 1-2)

1.1 Preface

One of the central tasks of engineering sciences is the most possibly exact description of technical processes with the goal of understanding the dynamic behavior of complex systems, of recognizing regularities, and thereby of making possible reliable statements about the future behavior of these systems. With regard to combustion engines as propelling systems for land, water, and air vehicles, for permanent and emergency generating sets, as well as for air conditioning and refrigeration, the analysis of the entire process thus acquires particular importance.

In the case of model-based parameter-optimization, engine behavior is described with a mathematical model. The optimization does not occur in the real engine, but rather in a model, which takes into account all effects relevant for the concrete task of optimization. The advantages of this plan are a drastic reduction of the experimental cost and thus a clear saving of time in developmental tasks, see Kuder and Kruse (2000).

The prerequisite for simulation are mechanical, thermodynamic, and chemical models for the description of technical processes, whereby the understanding of thermodynamics and of chemical reaction kinetics are an essential requirement for the modeling of motor processes.

1.2 Model-building

The first step in numeric simulation consists in the construction of the model describing the technical process. Model-building is understood as a goal-oriented simplification of reality through abstraction. The prerequisite for this is that the real process can be divided into single processual sections and thereby broken down into partial problems. These partial problems must then be physically describable and mathematically formulatable. A number of demands must be placed upon the resulting model:

• The model must be formally correct, i.e. free of inconsistencies. As regards the question of "true or false", it should be noted that models can indeed be formally correct but still not describe the process to be investigated or not be applicable to it. There are also cases in which the model is physically incorrect but nevertheless describes the process with sufficient exactness, e.g. the Ptolemaic model for the simulation of the dynamics of the solar system, i.e. the calculation of planetary and lunar movement.

• The model must describe reality as exactly as possible, and, furthermore, it must also be mathematically solvable. One should always be aware that every model is an approximation to reality and can therefore never perfectly conform with it. • The cost necessary for the solution of the model with respect to the calculation time must be justifiable in the context of the setting of the task.

• With regard to model-depth, this demand is applicable: as simple as possible and as complex as necessary. So-called universal models are to be regarded with care.

It is only by means of the concept of model that we are in the position truly to comprehend physical processes.

In the following, we will take a somewhat closer look into the types of models with regard to the combustion engine. It must in the first place be noted that both the actual thermodynamic cycle process (particularly combustion) and the change of load of the engine are unsteady processes. Even if the engine is operated in a particular operating condition (i.e. load and rotational speed are constant), the thermodynamic cycle process runs unsteadily. With this, it becomes obvious that there are two categories of engine models, namely, such that describe the operating condition of the engine (total-process models) and such that describe the actual working process (combustion models).

With respect to types of models, one distinguishes between:

• linguistic models, i.e. a rule-based method built upon empirically grounded rules, which cannot be grasped by mathematical equations, and
• mathematical models, i.e. a method resting on mathematical formalism.

Linguistic models have become known in recent times under the concepts "expert systems" and "fuzzy-logic models". Yet it should thereby be noted that rule-based methods can only interpolate and not extrapolate. We will not further go into this type of model. Mathematical models can be subdivided into:

• parametric, and
• non-parametric

models. Parametric models are compact mathematical formalisms for the description of system behavior, which rests upon physical and chemical laws and show only relatively few parameters that are to be experimentally determined. These models are typically described by means of a set of partial or normal differential equations.

Non-parametric models are represented by tables that record the system behavior at specific test input signals. Typical representatives of this type of model are step responses or frequency responses. With the help of suitable mathematical methods, e.g. the Fourier transformation, the behavior of the system can be calculated at any input signal.

Like linguistic models, non-parametric models can only interpolate. Only mathematical models are utilized for the simulation of the motor process. But because the model parameters must be adjusted to experimental values in the case of these models as well, they are fundamentally error-prone. These errors are to be critically evaluated in the analysis of simulation results. Here too, it becomes again clear that every model represents but an approximation of the real system under observation.

1.3 Simulation

For the construction of parametric mathematical models for the simulation of temporally and spatially variable fluid, temperature, and concentration fields with chemical reactions, the knowledge of thermodynamics, fluid dynamics, and of combustion technology is an essential prerequisite, see Fig. 1.1.