Development of a spark discharge model for predicting ignition stability in high EGR conditions in SI engines

Recently, EGR (Exhaust Gas Recirculation) combustion has been used to enhance the thermal efficiency of internal combustion engines. However, EGR combustion causes ignition instability, leading to increased cycle-to-cycle combustion variability and misfire rates. To improve ignition stability under high EGR conditions, it is essential to elucidate the ignition mechanism and develop a predictive model that incorporates this mechanism. In particular, short-circuiting and restriking of spark channels are critical elements to model, as they directly influence flame kernel formation. Experiments using the RCM (Rapid Compression Machine) has demonstrated that ignition stability varies with changes in the flow velocity near the spark plug and the EGR ratio. Additionally, when misfire occurs, the flame kernel forms in small pieces due to a spark short circuit and then extinguishes. The model developed in this study combines a space potential model and a discharge path search model, which can reproduce the flame kernel behavior and EGR limits observed in experiments.