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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.
The virtual development of future Spark Ignition (SI) engine combustion processes in three-dimensional Computational Fluid Dynamics (3D-CFD) demands for the integration of detailed chemistry, enabling - additionally to the 3D-CFD modelling of flow and mixture formation - the prediction of fuel-dependent SI engine combustion in all of its complexity. This work presents an approach, which constitutes a coupled solution for flame propagation, auto-ignition, and emission formation modelling incorporating detailed chemistry, while exhibiting low computational costs. For modelling the regular flame propagation, a laminar flamelet approach, the G-equation is used. Auto-ignition phenomena are addressed using an integrated flamelet approach, which bases on the tabulation of fuel-dependent reaction kinetics. By introducing a progress variable for the auto-ignition - the Ignition Progress Variable (IPV) - detailed chemistry is integrated in 3D-CFD. The modelling of emission formation bases on an interactively coupled flamelet approach, the Transient Interactive Flamelet (TIF) model. The functionality of the combined approach to model the variety of SI engine combustion phenomena is proved first in terms of fundamentals and standalone sub-model functionality studies by introducing a simplified test case, which represents an adiabatic pressure vessel without moving meshes. Following the basic functionality studies, the sub-model functionalities are investigated and validated in adequate engine test cases. It is shown, that the approach allows to detect locally occurring auto-ignition phenomena in the combustion chamber, and to model their interaction with regular flame propagation. Moreover, the approach enables the prediction of emission formation on cell level.
Downsizing of modern gasoline engines with direct injection is a key concept for achieving future CO22 emission targets. However, high power densities and optimum efficiency are limited by an uncontrolled autoignition of the unburned air-fuel mixture, the so-called spark knock phenomena. By a combination of three-dimensional Computational Fluid Dynamics (3D-CFD) and experiments incorporating optical diagnostics, this work presents an integral approach for predicting combustion and autoignition in Spark Ignition (SI) engines. The turbulent premixed combustion and flame front propagation in 3D-CFD is modeled with the G-equation combustion model, i.e. a laminar flamelet approach, in combination with the level set method. Autoignition in the unburned gas zone is modeled with the Shell model based on reduced chemical reactions using optimized reaction rate coefficients for different octane numbers (ON) as well as engine relevant pressures, temperatures and EGR rates. The basic functionality and sensitivities of improved sub-models, e.g. laminar flame speed, are proven in simplified test cases followed by adequate engine test cases. It is shown that the G-equation combustion model performs well even on unstructured grids with polyhedral cells and coarse grid resolution. The validation of the knock model with respect to temporal and spatial knock onset is done with fiber optical spark plug measurements and statistical evaluation of individual knocking cycles with a frequency based pressure analysis. The results show a good correlation with the Shell autoignition relevant species in the simulation. The combined model approach with G-equation and Shell autoignition in an active formulation enables a realistic representation of thin flame fronts and hence the thermodynamic conditions prior to knocking by taking into account the ignition chemistry in unburned gas, temperature fluctuations and self-acceleration effects due to pre-reactions. By the modeling approach and simulation methodology presented in this work the overall predictive capability for the virtual development of future knockproof SI engines is improved.
The present work is based on the need for understanding the in-cylinder flow and its subsequent effects on combustion in a valved-two-stroke spark ignition engine with fuel injection using Computational Fluid Dynamics (CFD) and experimental techniques. In this context, the CFD code KIVA-II has been modified to model the two-stroke engine gas exchange and combustion processes. A 3-D Cartesian grid generation program for complex engine geometry has been added to the KIVA code which has been modified to include intake and exhaust flow processes with valves. New and improved sub models for wall jet interaction, mixing controlled combustion and one dimensional wave action have also been incorporated. The modified version of the program has been used to simulate a fuel injected two-stroke spark ignition engine and parametric studies have been undertaken. The simulated flow, combustion and exhaust emission characteristics over a wide range of operating conditions show the expected trends in behaviour observed in actual engines. In the second phase of this study, the air-assisted-fuel-injection (AAFI) process into a cylinder has been simulated with a high resolution computational grid. The simulation results are presented and compared with experimental data obtained using the Schlieren optical technique. An approximate method based on the conservation of mass, momentum and energy of the spray jet and using a comparatively coarse grid has been suggested for simulating the AAFI process. The simulation study predicts a high degree of atomisation of fuel spray with Sauter mean diameter around 10 μm even with moderate air and fuel pressures. The penetration and width of spray are simulated within 15% of the experimental values. In the last phase of this study, the flow and combustion processes have been studied for a four-stroke spark ignition engine with the AAFI process. The simulation results obtained using this approximate method have been validated with experimental data ge.
The book provides a comprehensive overview of combustion models used in different types of spark ignition engines. In the first generation of spark ignition (SI) engines, the turbulence is created by the shear flow passing through the intake valves, and significantly decays during the intake and compression strokes. The residual turbulence enhances the laminar flame velocity, which is characteristic of the fuel and increases the relative effectiveness of the engine. In this simple two-zone model, the turbulence is estimated empirically; the spherical flame propagation model considers ignition delay, thermodynamics, heat transfer and chemical equilibrium, to obtain the performance and emissions of an SI engine. The model is used extensively by designers and research engineers to handle the fuel-air mixture prepared in the inlet and different geometries of open combustion chambers. The empiricism of the combustion model was progressively dismantled over the years. New 3D models for ignition considering the flow near a spark plug and flame propagation in the bulk gases were developed by incorporating solutions to Reynolds-averaged Navier-Stokes (RANS) equations for the turbulent flow with chemical reactions in the intense computational fluid dynamics. The models became far less empirical and enabled treating new generation direct-injection spark-ignition (DISI) gasoline and gas engines. The more complex layout of DISI engines with passive or active prechamber is successfully handled by them. This book presents details of models of SI engine combustion progressively increasing in complexity, making them accessible to designers, researchers, and even mechanical engineers who are curious to explore the field. This book is a valuable resource for anyone interested in spark ignition combustion.