Stratified Mixture Formation and Combustion Process for Wall-guided Stratified-charge DISI Engines with Different Piston Bowls by Simulation 2010-01-0595

This paper presents the simulation of in-cylinder stratified mixture formation, spray motion, combustion and emissions in a four-stroke and four valves direct injection spark ignition (DISI) engine with a pent-roof combustion chamber by the computational fluid dynamics (CFD) code. The Extended Coherent Flame Combustion Model (ECFM), implemented in the AVL-Fire codes, was employed. The key parameters of spray characteristics related to computing settings, such as skew angle, cone angle and flow per pulse width with experimental measurements were compared.

The numerical analysis is mainly focused on how the tumble flow ratio and geometry of piston bowls affect the motion of charge/spray in-cylinder, the formation of stratified mixture and the combustion and emissions (NO and CO₂) for the wall-guided stratified-charge spark-ignition DISI engine. But due to the fuel injected during compression stroke, the effect of intake ports and exhaust ports were not taken into consideration in this study. It is found that the geometry of piston bowls has a major effect on the mixture stratification in-cylinder, the combustion process and others. In addition, the characteristics of the charge motion and combustion, such as mean in-cylinder pressure, heat release rate and accumulated heat release vary as a function of crank angle at different injection timings and tumble flow ratios, based on one of two combustion geometries. The results show that the injection timing and piston bowl shape play very important roles for the combustion process and mixture stratification. Furthermore, the simulation provides an insight into the interaction of charge flow, fuel spray, piston bowl as well as combustion.