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About this book

Due to the large number of influencing parameters and interactions, the fuel injection and therewith fuel propagation and distribution are among the most complex processes in an internal combustion engine. For this reason, injection is usually the subject to highly detailed numerical modeling, which leads to unacceptably high computing times in the 3D-CFD simulation of a full engine domain. Marlene Wentsch presents a critical analysis, optimization and extension of injection modeling in an innovative, fast response 3D-CFD tool that is exclusively dedicated to the virtual development of internal combustion engines.

About the Author

Marlene Wentsch works as research associate in the field of 3D-CFD simulations of injection processes at the Institute of Internal Combustion Engines and Automotive Engineering (IVK), University of Stuttgart, Germany.

Table of Contents


Chapter 1. Introduction

The development of internal combustion engines is a very demanding task, which requires a deep understanding of thermodynamic processes and their influencing factors. The complexity and extensiveness, which has to be mastered, is additionally enhanced by constantly increasing requirements in terms of emissions, engine efficiency, performance and drivability as well as the introduction of new technologies like water injection and homogeneous charge compression ignition (HCCI) or test methods like real driving emissions (RDE). Shortened product life cycles and thus significantly reduced development times [47] moreover require time-saving processes in the development of new as well as the optimization of existing powertrain concepts.

Marlene Wentsch

Chapter 2. Simulation of Internal Combustion Engines

The virtual engine development is based on a well-considered integration of three main simulation tools: real working process calculation, one-dimensional (1D) CFD simulation and 3D-CFD simulation. Due to their strongly deviating temporal and spatial resolution, they have different modeling demands, input requirements and therefore fields of application. They highly differ in their degrees of complexity, predictive capability and computing time as illustrated in Figure 2.1.

Marlene Wentsch

Chapter 3. The 3D-CFD Tool QuickSim

The scope and focus of various 3D-CFD codes are just as diverse as their application areas. This can be the examination of an isolated process within a single cylinder on the one hand and the investigation of gas dynamics within the intake system of a turbocharged 4-cylinder engine on the other hand [75]. The present work does not aim at comparing different approaches and assessing their quality regarding simulation results accuracy, level of detail, etc.

Marlene Wentsch

Chapter 4. Fundamentals of Spray Modeling and Simulation

In preparation of the analyses discussed in Chapters 6 to 8, an introduction to the modeling of injection sub-processes as well as required terminologies and calculation formulas will be given in the following. This includes fuel properties, spray atomization processes and the numerical injection definition as influencing parameters on the spray development and mixture formation (compare Figure 1.2).

Marlene Wentsch

Chapter 5. Utilized Engine Models

The fuel injection analyses presented in this work were carried out on different project-specific engine models, which will be introduced in the following. Although some units have been modified during the tests, only the standard configurations are listed. Deviations from this will be stated separately, if relevant.

Marlene Wentsch

Chapter 6. Numerical Boundary Conditions

A comprehensive analysis of purely numerical influencing factors on the fuel injection forms the basis of this work. The majority of conducted simulations utilized variants of the virtual injection chamber, introduced in Chapter 5.1. This enables an isolated examination of the injection process and ensures a reliable reproduction of conditions for the purpose of comparability.

Marlene Wentsch

Chapter 7. Liquid Fuel Modeling

The modeling of highly complex in-cylinder processes is characterized by the employment of severe simplifications. This is done, in particular, in the numerical description of fuel. The fact that liquid fuel consists of a multitude of components, for example, is commonly neglected in most multi-dimensional models.

Marlene Wentsch

Chapter 8. Parametrization of Injector Properties

The previous chapters covered numerical boundary conditions as well as fuel modeling as basic influencing factors on the fuel injection simulation. In addition, application or project specific challenges may ensue which need to be mastered. Here, the major challenge is to utilize limited input as best as possible and derive the corresponding injection parameters for the simulation with QuickSim.

Marlene Wentsch

Chapter 9. Conclusion and Outlook

In the present work, sensitivities and specifics of the fuel injection modeling in conformity with the 3D-CFD Tool QuickSim could be determined and best practice solutions identified. These particularly related to numerical framework conditions, the modeling of fuel and parameterization of the injector geometry.

Marlene Wentsch


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