An Innovative 3D-CFD-Approach towards Virtual Development of Internal Combustion Engines

Acknowledgments

Table of Contents

Abstract

Zusammenfassung

Symbols, Subscripts and Abbreviations

Roman Symbols

Greek Symbols

Subscripts and Abbreviations

1 Introduction

1.1 Society and Transportation

1.2 The Fascination of Internal Combustion Engines

1.3 Internal Combustion Engines and Sustainable Transportation

1.3.1 Development Targets of Internal Combustion Engines in the Past

1.3.2 The Role of Alternative Engine Concepts

1.3.3 Development Targets of Internal Combustion Engines in the Future

1.3.3.1 General Improvement of actual Solutions

1.3.3.2 Downsizing and Turbo-Charging

1.3.3.3 Hybridization

1.3.3.4 Development of Innovative Combustion Solutions

1.3.3.5 Alternative Fuels

1.4 How to Face the Complexity of Future Internal- Combustion-Engines

2 Simulation of Internal Combustion Engines

2.1 Simulation towards Virtual Engine Development

2.1.1 One Tool for the Simulation of the Entire Engine?

2.1.1.1 Mechanical Numerical Analysis

2.1.1.2 Engine Operating Cycle Analyses

2.1.2 The Future Challenge: an improved Integration of Simulation Tools

2.2 Today’s Repartition of the Resources in Engine Development

2.3 Introduction to Engine Processes Modeling in the Simulation of the Operating Cycle

3 Engine Energy- Balance

3.1 Energy-Balance of the Combustion Chamber

3.2 Energy-Balance of the Entire Engine

3.3 The Role of Engine Energy-Balance in the Engine Development Process

4 Real Working-Process Analysis

4.1 Introduction

4.2 Fundamental Equations

4.3 Thermal State Equation of the Working Fluid

4.4 Engine Modeling (Engine-Specific Models)

4.4.1 Modeling of the Thermo-Physical Properties of the Working Fluid

4.4.2 Modeling of the Wall Heat-Transfer

4.4.3 Modeling of the Combustion Process

4.4.3.1 Empirical Models

4.4.3.2 Quasi-dimensional Models

4.5 Two Approaches in the Calculation of the Real Working-Process

4.5.1 Pressure Profile Calculation - Combustion Profile Supply

4.5.2 Combustion Profile Calculation - Pressure Profile Supply

4.6 The Role of Real Working-Process Analysis in the Engine Development Process

5 One-Dimensional Simulation (1D-CFD-Simulation)

5.1 Introduction

5.2 Engine Layout and Conservation Equations

5.3 The Role of the 1D-CFD-Simulation in the Engine Development Process

6 Three-Dimensional Simulation (3D-CFD Simulation)

6.1 Fundamental Equations

6.1.1 Mass Conservation Equation

6.1.2 Species Mass Conservation Equation

6.1.3 Momentum Conservation Equation (Navier-Stokes’ Equation)

6.1.4 Energy Conservation Equation

6.2 Engine Modeling

6.2.1 Universally-Valid 3D-CFD-Models

6.2.1.1 Modeling of the Thermo-physical Properties of the Working Fluid

6.2.1.2 Modeling of Non-Convective Processes

6.2.1.3 Turbulence Modeling

6.2.1.4 Combustion Models

6.2.1.5 Wall Heat-Transfer Models

6.2.2 Introduction to Engine-Specific 3D-CFD-Models

6.3 Discretization Practices (Numerical Implementation)

6.3.1 Spatial Flux Discretization

6.3.1.1 Low-Order Differencing Scheme – Upwind Differencing (UD)

6.3.1.2 Higher-Order Differencing Scheme

6.4 The Role of the 3D-CFD-Simulation in the Engine Development Process

7 Towards an improved 3D-CFD- Simulation

7.1 An innovative Fast-Response 3D-CFD-Tool: QuickSim

7.1.1 Fast Analysis

7.1.1.1 Mesh Discretization for DNS Simulations

7.1.1.2 Mesh Discretization for LES Simulations

7.1.1.3 Mesh Discretization for QuickSim Simulations

7.1.2 Reliable Calculation

7.1.3 User-Friendliness

7.1.4 Clear Representation of the Results

7.1.5 Cost Efficiency

7.1.5.1 Processor Utilization for QuickSim Simulations

7.2 Additional Features of QuickSim

7.2.1 Simulation of several successive Engine Operating Cycles

7.2.2 Extension of the 3D-CFD-Domain up to a Full-Engine Simulation

7.2.3 The Simulation of a Flow Test-Bench

7.3 Summary of the QuickSim Features

7.4 QuickSim’s Calculation Layout

8 3D-CFD-Modeling of the Thermodynamic Properties of the Working Fluid

8.1 Introduction

8.2 Chemical Composition of the Working Fluid Mixture

8.2.1 One-Step Fuel-Oxidation Reaction Mechanism

8.2.2 The Reality: More than Thousand Intermediate Products

8.3 Traditional Approach

8.4 QuickSim’s Approach: Few Species for the Description of the Working Fluid

8.4.1 QuickSim’s Approach: A universally-valid Chemical Reaction Scheme for the Description of Burned Gas

8.4.1.1 Chemical Equilibrium Assumption

8.4.1.2 The proposed Chemical Reaction Scheme

8.4.1.3 A “frozen” Composition at low Temperatures

8.4.1.4 Results: The Chemical Composition of Burned Gas

8.4.2 QuickSim’s Approach: Conclusive Modeling of the Thermodynamic Properties of Burned Gas

8.4.2.1 Heat Release at the Flame Front and Post-Oxidation of Exhaust Gas with Fresh Gas

8.4.2.2 Heat Exchange due to Dissociation Effects and Post-Oxidation within Exhaust Gas

8.4.2.3 Combustion Conversion Efficiency

9 3D-CFD-Modeling of the Combustion for SI-Engines

9.1 Introduction

9.2 Flame Propagation Modeling (Weller Model)

9.3 QuickSim’s Approach: Implementation Improvement

9.3.1 Numerical Implementation of the Flame Propagation Model

9.3.2 Numerical Inconsistencies at the Flame Front

9.3.2.1 Expedients for the Numerical Inconsistencies at the Flame Front

9.3.3 Local Two-Zones Model

9.3.4 Ignition Model

9.3.5 Final Implementation Procedure

9.4 Results

10 3D-CFD-Modeling of the Wall Heat-Transfer

10.1 Introduction

10.1.1 Phenomena Understanding, Calculation Approach and Considerations

10.2 State-of the-Art of Engine Heat-Transfer Calculationin the 3D-CFD-Simualtion

10.2.1 The Wall Function Approach

10.2.2 Low Reynolds Number Models

10.2.3 Phenomenological Heat-Transfer Models in the Real Working-Process Analysis (WP)

10.2.3.1 Motivation for a Phenomenological Approach

10.2.3.2 Woschni’s Correlation

10.2.3.3 Hohenberg’s Correlation

10.2.3.4 Bargende’s Correlation

10.2.4 Comparison between the 3D-CFD-Heat-Transfer (Wall- Function Model) and the Real Working-Process Analysis

10.2.4.1 Sensitivity Analysis of the 3D-CFD-Heat-Transfer calculated with a Wall-Function Model

10.2.5 QuickSim’s Approach: A new Phenomenological Heat- Transfer Model in the 3D-CFD-Simulation

10.2.5.1 The Heat-Transfer during the Working Cycle

10.2.5.2 The Heat-Transfer during the Charge Changing Period

10.3 Results

10.4 Influence of 3D-CFD-Heat-Transfer-Models on the Engine Energy-Balance

11 A Way towards Virtual Engine Development

11.1 Introduction

11.2 The Hardware: a turbocharged CNG Race-Engine

11.3 Setting of the 3D-CFD-Simulation

11.3.1 Initial Conditions and Properties of the Working Fluid

11.3.2 Boundary Conditions

11.4 CNG-Injector Model

11.4.1 Traditional Gas Injection Modeling

11.4.2 Gas Injection Modeling in QuickSim

11.5 3D-CFD-Domains limited to the Cylinder

11.5.1 3D-CFD-Simulation excluding the Fuel Injectors

11.5.2 3D-CFD-Simulation including the Fuel Injectors

11.6 Extension of the 3D-CFD-Domain: One Cylinder with the Airbox

11.6.1 Between Predictability and Results Consistency

11.6.1.1 QuickSim’s Improved Approach: The integrated 0D- and1D-CFD Simulationof the missing Cylinders

11.7 3D-CFD-Simulation of the Full Engine

11.7.1 Results and 3D-CFD-Flow Field Investigations on the Full Engine

11.7.1.1 Mixture Formation

11.7.1.2 Residual Gas Distribution

11.7.1.3 Turbulence

11.7.1.4 Combustion

11.7.1.5 Convergence of the Results

11.7.2 Result Comparison among different Operating Conditions

11.8 The Simulation of successive Operating Cycles

11.9 Result Comparison among the different Extensions of the 3D-CFD-Domain

12 Conclusion

13 Outlook

Appendix A

A.1 Vector and Matrix Analysis

Appendix B

B.1 Thermodynamic Properties of the Working Fluid

References