Computational study of the effects of the geometry of the piston bowl pip for a high-speed direct injection diesel engine

Abstract

The piston bowl design is one of the most important factors that affect the air/fuel mixing and the subsequent combustion and pollutant formation processes in a direct injection diesel engine. The bowl geometry and dimensions, such as the pip region, the bowl lip area and the torus radius, are all known to have an effect on the in-cylinder mixing and combustion process. In order to understand better the effect of the pip region, three piston bowls with different pip designs but with the same lip area and torus radius were designed and investigated using computational fluid dynamics (CFD) engine modelling. A commercial CFD KIVA3V with improved submodels was used to model the in-cylinder flows and combustion process, and it was validated on a high-speed direct injection (HSDI) engine with a second-generation common rail fuel injection system. The engine performance, in-cylinder flow and combustion and emission characteristics were analysed at maximum power and maximum torque conditions and at part-load operating conditions. Three injector protrusions and injection timings were investigated at full load conditions. The effect of injection timing and exhaust gas recirculation (EGR) at the part-load condition was considered.