The stratified combustion model of direct-injection spark-ignition engines

This paper presents a new model for stratified combustion in direct-injection spark-ignition (DISI) engines, which considers the secondary diffusion flame in the burned region and the effect of mixturefraction fluctuation on the laminar burning velocity. For primary flame propagation, Weller's flame area evolution (FAE) model was adopted and extended to partially premixed combustion by implementing the variance of mixture fraction and the concept of probability density. A two-step reaction mechanism of water-gas shift and hydrogen oxidation was applied to a diffusion flame with equilibrium concentrations of CO, CO 2 , H 2 , and H 2 O in the burned gas. In addition to these models, a new correlation of the laminar burning velocity was adopted, which can be applicable to a much wider range of equivalence ratio, pressure, and temperature than the other models. The direct-injection gasoline spray model was implemented in order to form a stratified fuel/air mixture. Under stratified-charge conditions, three-dimensional simulation was performed in a direct-injection spark-ignition engine geometry by using STAR-CD. The simulation results can help us understand the combustion process in DISI engines. The present model simulates the characteristics of flame propagation, diffusion reaction, concentrations of products in the burned region, and burned-gas temperature.