Simulation-Based Evaluation of Spark-Assisted Compression Ignition Control for Production

Spark-assisted compression ignition (SACI) leverages flame propagation to trigger autoignition in a controlled manner. The autoignition event is highly sensitive to several parameters, and thus, achieving SACI in production demands a high tolerance to variations in conditions. Limited research is available to quantify the combustion response of SACI to these variations. A simulation study is performed to establish trends, limits, and control implications for SACI combustion over a wide range of conditions. The operating space was evaluated with a detailed chemical kinetics model. Key findings were synthesized from these results and applied to a 1-D engine model. This model identified performance characteristics and potential actuator positions for a production-viable SACI engine. This study shows charge preparation is critical and can extend the low-load limit by strengthening flame propagation and the high-load limit by reducing ringing intensity. The simulation results also suggest that under certain operating conditions, there can be a significant disparity between the autoignition sensitivity to temperature and pressure. This may dictate different load control or combustion phasing control strategies, and these results are likely fuel specific. The simulation also indicates that production-feasible control actuator positions can achieve SACI from about 2-10 bar BMEP within flammability, ringing intensity, and knock constraints.