Simulation of SACI Autoignition Phasing Sensitivity for Production Controls Strategies 2020-01-1145
Spark-assisted compression ignition (SACI) is a combustion strategy that leverages flame propagation to trigger autoignition. The autoignition event is highly sensitive to several parameters, and thus, achieving SACI in production demands a robust response to variations in conditions. However, limited research is available to quantify the combustion response of SACI to these variations. A simulation study is performed to identify the sensitivity in autoignition timing as ethanol content, fuel RON, air-fuel ratio, EGR level, and the phasing of flame propagation are swept. An experimentally-validated one-dimensional simulation model provides the composition, state, and flow metrics at BDC. The results are applied to the Leeds diagram to ensure the conditions are viable for flame propagation. The conditions at BDC are then transferred to a chemical kinetics solver, where autoignition is modeled using a detailed chemical kinetics mechanism. These results are used to explore the SACI combustion controls space. The range of CA50 control authority is particularly important as combustion phasing is used to perform rapid torque changes. The steady-state combustion control authority is evaluated, and potential controls implications are described in detail. The analysis of combustion response is evaluated over simple transient maneuvers and potential challenges are identified. The chemical kinetics mechanism used in this analysis is unlikely to be computationally feasible for real-time control. Several empirical autoignition models are evaluated that have a lower computational load. The results of the empirical models are compared to those of the kinetics mechanism.