Understanding highly complex nature of flow in an IC engine is essential to optimize its performance. However, the events like reciprocating motion of piston, motion of valves, turbulence generation, spray and mixing lead to a complex flow pattern. CFD is very useful in computing and understanding this complex flow pattern. In this book, all aspects of CFD technique to simulate the mixing of fuel with air in GDI engines are explained. The book covers the governing equations, numerical techniques for solving them, method of analysis of data (in the context of mixing processes) and programming techniques. The book will be useful for professionals who are performing CFD analysis using CFD softwares for thermal systems specifically reciprocating systems like engines, compressors and systems involving sprays, mixing etc. It is also useful for those who are developing CFD tools.