Modelling Diesel Combustion


Book Description

This book comprehensively discusses diesel combustion phenomena like ignition delay, fuel-air mixing, rate of heat release, and emissions of smoke, particulate and nitric oxide. It enables quantitative evaluation of these important phenomena and parameters. Most importantly, it attempts to model them with constants that are independent of engine types and hence they could be applied by the engineers and researchers for a general engine. This book emphasizes the importance of the spray at the wall in precisely describing the heat release and emissions for most of the engines on and off-road. It gives models for heat release and emissions. Every model is thoroughly validated by detailed experiments using a broad range of engines. The book describes an elegant quasi-one-dimensional model for heat release in diesel engines with single as well as multiple injections. The book describes how the two aspects, namely, fuel injection rate and the diameter of the combustion bowl in the piston, have enabled meeting advanced emission, noise, and performance standards. The book also discusses the topics of computational fluid dynamics encompassing RANS and LES models of turbulence. Given the contents, this book will be useful for students, researchers and professionals working in the area of vehicle engineering and engine technology. This book will also be a good professional book for practising engineers in the field of combustion engines and automotive engineering.




A Multi-dimensional Flamelet Model for Ignition in Multi-feed Combustion Systems


Book Description

This work develops a computational framework for modeling turbulent combustion in multi-feed systems that can be applied to internal combustion engines with multiple injections. In the first part of this work, the laminar flamelet equations are extended to two dimensions to enable the representation of a three-feed system that can be characterized by two mixture fractions. A coupling between the resulting equations and the turbulent flow field that enables the use of this method in unsteady simulations is then introduced. Models are developed to describe the scalar dissipation rates of each mixture fraction, which are the parameters that determine the influence of turbulent mixing on the flame structure. Furthermore, a new understanding of the function of the joint dissipation rate of both mixture fractions is discussed. Next, the extended flamelet equations are validated using Direct Numerical Simulations (DNS) of multi-stream ignition that employ detailed finite-rate chemistry. The results demonstrate that the ignition of the overall mixture is influenced by heat and mass transfer between the fuel streams and that this interaction is manifested as a front propagation in two-dimensional mixture fraction space. The flamelet model is shown to capture this behavior well and is therefore able to accurately describe the ignition process of each mixture. To provide closure between the flamelet chemistry and the turbulent flow field, information about the joint statistics of the two mixture fractions is required. An investigation of the joint probability density function (PDF) was carried out using DNS of two scalars mixing in stationary isotropic turbulence. It was found that available models for the joint PDF lack the ability to conserve all second-order moments necessary for an adequate description of the mixing field. A new five parameter bivariate beta distribution was therefore developed and shown to describe the joint PDF more accurately throughout the entire mixing time and for a wide range of initial conditions. Finally, the proposed model framework is applied in the simulation of a split-injection diesel engine and compared with experimental results. A range of operating points and different injection strategies are investigated. Comparisons with the experimental pressure traces show that the model is able to predict the ignition delay of each injection and the overall combustion process with good accuracy. These results indicate that the model is applicable to the range of regimes found in diesel combustion.




Modeling Engine Spray and Combustion Processes


Book Description

The utilization of mathematical models to numerically describe the performance of internal combustion engines is of great significance in the development of new and improved engines. Today, such simulation models can already be viewed as standard tools, and their importance is likely to increase further as available com puter power is expected to increase and the predictive quality of the models is constantly enhanced. This book describes and discusses the most widely used mathematical models for in-cylinder spray and combustion processes, which are the most important subprocesses affecting engine fuel consumption and pollutant emissions. The relevant thermodynamic, fluid dynamic and chemical principles are summarized, and then the application of these principles to the in-cylinder processes is ex plained. Different modeling approaches for the each subprocesses are compared and discussed with respect to the governing model assumptions and simplifica tions. Conclusions are drawn as to which model approach is appropriate for a specific type of problem in the development process of an engine. Hence, this book may serve both as a graduate level textbook for combustion engineering stu dents and as a reference for professionals employed in the field of combustion en gine modeling. The research necessary for this book was carried out during my employment as a postdoctoral scientist at the Institute of Technical Combustion (ITV) at the Uni versity of Hannover, Germany and at the Engine Research Center (ERC) at the University of Wisconsin-Madison, USA.




Fundamentals of Fuel Injection and Emission in Two-Stroke Engines


Book Description

The main goal of the book is the presentation of the last theoretical and experimental works concerning fuel injection systems, mainly in small power two-stroke engines as well as in marine engines. This book includes thirteen chapters devoted to the processes of fuel injection and the combustion that takes place in a stratified charge within the cylinders of two-stroke engines. In the first two chapters, the division into different injection systems in two-stroke engines and each injection system is briefly described. Various theoretical and practical solutions of fueling system designs are described. In Chapter Three, mathematical models, the spatial movement of gas in the cylinder and the combustion chamber are introduced, taking into account the turbulence of the charge. Chapter Four relates to the behavior of fuel injected into the gaseous medium, including evaporation processes, disintegration and processes occurring while the fuel drops connect with the wall. The next section describes the zero-dimensional model of fuel injection in two-stroke engines along with examples of numerical calculations. The sixth chapter is devoted to CFD multi-dimensional models of movement and evaporation of the fuel in a closed gaseous medium, occurring also in other engine types. Chapter Seven describes a two-zone model of the combustion process and the effect of the geometry of the combustion chamber on the flame propagation with a simplified verification model of combustion. Chapter Eight compares the propagation phase of gas and liquid fuels concerning direct fuel injection as well as the direct fuel injection from the cylinder head and the thermodynamic parameters of the charge. The formation of the components during the combustion process in the direct fuel injection two-stroke engine was obtained by numerical calculations and results are discussed in Chapter Nine. Chapter Ten describes the parameters of the two-stroke engine with a direct fuel injection carried out at the Cracow University of Technology. Additionally, the chapter presents CFD simulations of fuel propagation and combustion processes, taking into account the formation of toxic components and exhaust gas emission. The processes of two direct rich mixture injection systems FAST and RMIS developed in CUT are presented in Chapter Eleven. Miscellaneous problems of direct fuel injection, such as characteristics of fuel injectors, problems of direct gaseous fuel injection, and the application of fuelling systems in outboard engines and snowmobile vehicles are presented in Chapter Twelve. A comparison of working parameters in two- and four stroke engines is also mapped out. The last chapters contain the final conclusions and remarks concerning fuel injection and emission of exhaust gases in small two-stroke engines. This book is a comprehensive monograph on fuel injection. The author presents a series of theoretical and design information from his own experience and on the basis of the works of other authors. The main text intends to direct fuel injection with respect to gas motion in the combustion chamber and influence the injection parameters for exhaust emission. The book presents its own theoretical work and experimental tests concerning a two-stroke gasoline engine with electrically controlled direct fuel injection. The book describes the processes of a general nature also occurring in other types of engines and presents a comparison of different injection systems on working parameters and gas emission. The book contains 294 images, 290 equations and 16 tables obtained from the CFD simulation and experimental works.




Modelling Diesel Combustion


Book Description

Phenomenology of Diesel Combustion and Modeling Diesel is the most efficient combustion engine today and it plays an important role in transport of goods and passengers on land and on high seas. The emissions must be controlled as stipulated by the society without sacrificing the legendary fuel economy of the diesel engines. These important drivers caused innovations in diesel engineering like re-entrant combustion chambers in the piston, lower swirl support and high pressure injection, in turn reducing the ignition delay and hence the nitric oxides. The limits on emissions are being continually reduced. The- fore, the required accuracy of the models to predict the emissions and efficiency of the engines is high. The phenomenological combustion models based on physical and chemical description of the processes in the engine are practical to describe diesel engine combustion and to carry out parametric studies. This is because the injection process, which can be relatively well predicted, has the dominant effect on mixture formation and subsequent course of combustion. The need for improving these models by incorporating new developments in engine designs is explained in Chapter 2. With “model based control programs” used in the Electronic Control Units of the engines, phenomenological models are assuming more importance now because the detailed CFD based models are too slow to be handled by the Electronic Control Units. Experimental work is necessary to develop the basic understanding of the pr- esses.