In the last few decades, application of advanced combustion technologies, engine design modifications, after-treatment techniques, etc. have improved engine performance and reduced exhaust emissions. However, advancement in technologies introduced a large number of parameters, which need to be optimised for satisfactory results. This increases the system complexity therefore it become very difficult to perform experiments for optimization of each parameter. In recent years, simulation techniques have shown their potential to resolve this issue. Simulation techniques can optimize such complex systems and provide optimized solution with less effort involvement. Optical diagnostic techniques are the other important area for internal combustion engines. These techniques can provide information about in-cylinder conditions, spray parameters, fuel-air mixing and combustion, which is not possible with conventional techniques. This book is based on these simulation and optical diagnostic techniques and provides case studies to resolve several technical issues involved with internal combustion engines. Few chapters based on advanced topics such as microwave-assisted plasma ignition, laser ignition, etc. are the important aspect of this book. Chapters are based on review of state-of-the-art models for combustion, with special focus on the theory, development and applications of these combustion models in internal combustion systems make this book suitable for researchers, working in the area of alternative fuels and advanced combustion techniques.