5. Modeling and Simulation of Diesel Engines Using CFD and Its Applications in Optimizing Various In-Cylinder Techniques

A four-stroke IC engine cycle undergoes the following processes—intake, compression, combustion, expansion and exhaust, which are governed by complex fluid dynamics, chemical kinetics and heat transfer phenomena and occur in milli/nanosecond timescales inside the engine cylinder making it difficult to visualize experimentally. A better understanding of the in-cylinder phenomena helps design better engines in terms of performance, fuel consumption and emissions. Optimization of the engine processes through physical testing can be time and cost intensive. CFD analysis helps visualize the various in-cylinder processes, analyze them better and evaluate various engine optimization parameters without having to test on an actual engine, hence it is comparatively effortless to do back-to-back comparisons to identify the effect of a single parameter, which reduces the engine development time and cost drastically. CFD analysis of Diesel engines is particularly useful since there are many in-cylinder optimization parameters in a diesel engine in comparison with a conventional gasoline engine, due to the direct injection and heterogeneous nature of combustion. This chapter aims to give an overview of the general methodology followed in performing CFD simulations in diesel engines towards the objective of enhancing the performance and minimizing the fuel consumption and emissions. Here a comprehensive coverage of the complete process of modeling and simulation is attempted, starting with the basic input data required, typical assumptions used, fundamental governing equations and discretization, model formulation, initial conditions, boundary conditions, model validation, various sub-models used and the analysis of results. The effect of in-cylinder techniques like combustion chamber geometry, injection timing, multiple injections and exhaust gas recirculation on performance and emissions is discussed through a brief review of published literature. It is hoped that the reader will get an insight into the procedure followed in diesel engine CFD analysis and some of its applications in the optimization through various in-cylinder techniques.