7 - Design and optimization of gasoline direct injection engines using computational fluid dynamics

Abstract

This chapter discusses the role of computational fluid dynamics (CFD) modeling in gasoline direct injection (DI) engine combustion system design and development. It starts with a brief review of injector technologies and the impact of the spray characteristics on the combustion system optimization. The main challenges to the optimization of a homogeneous-charge DI combustion system are to improve volumetric efficiency and fuel–air mixing homogeneity with reduced surface fuel wetting. Examples are included to demonstrate how CFD modeling is utilized to optimize the intake port design for improved flow capacity while providing adequate in-cylinder flow motion, to optimize combustion chamber design to improve fuel–air mixing at high speed and high load condition by alleviating the impact of intake flow on fuel spray, and to optimize fuel injection and cam strategy for improved fuel–air mixing homogeneity. For stratified-charge operation, CFD modeling has been applied to optimize the matching between intake flow motion and the spray configuration to generate stable charge stratification with the least amount of smoke emissions over a wide operation window. The boosted DI combustion system promotes its unique challenges in fuel–air mixing, knock mitigation, and higher heat flux requirement for catalyst warm-up in turbo-charged Di engines. However, it also provides further opportunity for combustion system optimization with fewer requirements on intake flow capacity. CFD modeling has been applied to optimize the intake port design to improve in-cylinder flow motion and mixing homogeneity. This chapter also provides a perspective view of CFD modeling in future combustion system development. CFD computational speed and simulation accuracy are two equally important aspects of CFD simulation in combustion system development and optimization. Better physical models are essential to the development of future advanced combustion systems with better fuel economy, higher power density, and cleaner emissions.