Control-oriented modeling of spark assisted compression ignition using a double Wiebe function

Spark assisted compression ignition (SACI) is currently under exploration as a combustion strategy to extend the operating range of homogeneous charge compression ignition (HCCI), which provides efficiency benefits over standard spark ignition (SI) combustion. This paper presents a physics-based control-oriented approach to modeling combustion in SACI. A double-Wiebe function is developed to capture the two-stage energy release seen in SACI, where a portion of the fuel is burned through flame propagation initiated by a spark, which then initiates auto-ignition in the remaining fuel. This double-Wiebe function is incorporated into a previously developed continuous-time model of HCCI combustion, and correlations for the Wiebe function parameters are developed based on physical model states. A simpler cycle-by-cycle HCCI model is also extended with a two-step energy release description for SACI combustion. Both models accurately capture the behavior of SACI and its sensitivity to different actuators when compared to experimental data.