Combustion Simulations In Diesel Engines Using Reduced Reaction Mechanisms

Three models were implemented, which are important for pollutant prediction in Diesel engines: ignition, chemistry and radiation. Ignition was tracked by means of a representative species (here CO), whose concentration remains small during the ignition period and which shows an increase at ignition. Its reaction rate was obtained from a detailed mechanism and combined with a presumed probability density function (pdf). The intrinsic low-dimensional manifold (ILDM) method was used as a chemistry model. It is an automatic reduction of a detailed chemical mechanism based on a local timescale analysis. It was also combined with a presumed pdf method. NOx and soot were predicted using a Zeldovich model and a phenomenological two-equation model, respectively. The radiative properties of the gases were described with a weighted sum of grey gases model (WSGGM). The radiative properties of soot were described by a grey model. The RTE was solved using the discrete ordinates method (DOM), which involves solving the RTE in discrete directions. The ignition and chemistry models were implemented in a standard CFD code, KIVA and used to simulate the combustion in a Caterpillar engine, for which experimental data were available. Ignition was observed to occur at the edge of the spray, in the lean region. Simulated pressure curves and mean NO concentrations were compared to experimental data and showed good agreement. Soot was strongly under-predicted due to the inability to identify the ILDM in the rich region. The DOM radiation model was tested in a furnace, and the wall fluxes were compared to analytical data. It was not used in the engine due to low quantities of soot predicted. Instead, an optically thin model was used in the engine and the radiative losses were seen to be negligible.

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.

Combustion has played a central role in the development of our civilization which it maintains today as its predominant source of energy. The aim of this book is to provide an understanding of both fundamental and applied aspects of low-temperature combustion chemistry and autoignition. The topic is rooted in classical observational science and has grown, through an increasing understanding of the linkage of the phenomenology to coupled chemical reactions, to quite profound advances in the chemical kinetics of both complex and elementary reactions. The driving force has been both the intrinsic interest of an old and intriguing phenomenon and the centrality of its applications to our economic prosperity. The volume provides a coherent view of the subject while, at the same time, each chapter is self-contained.

Computational Optimization of Internal Combustion Engines presents the state of the art of computational models and optimization methods for internal combustion engine development using multi-dimensional computational fluid dynamics (CFD) tools and genetic algorithms. Strategies to reduce computational cost and mesh dependency are discussed, as well as regression analysis methods. Several case studies are presented in a section devoted to applications, including assessments of: spark-ignition engines, dual-fuel engines, heavy duty and light duty diesel engines. Through regression analysis, optimization results are used to explain complex interactions between engine design parameters, such as nozzle design, injection timing, swirl, exhaust gas recirculation, bore size, and piston bowl shape. Computational Optimization of Internal Combustion Engines demonstrates that the current multi-dimensional CFD tools are mature enough for practical development of internal combustion engines. It is written for researchers and designers in mechanical engineering and the automotive industry.