A Review of Spark-Assisted Compression Ignition (SACI) Research in the Context of Realizing Production Control Strategies

This paper seeks to identify key input parameters needed to achieve a production-viable control strategy for spark-assisted compression ignition (SACI) engines. SACI is a combustion strategy that uses a spark plug to initiate a deflagration flame that generates sufficient ignition energy to trigger autoignition in the remaining charge. The flame propagation phase limits the rate of cylinder pressure rise, while autoignition rapidly completes combustion. High dilution within the autoignited charge is generally required to maintain reaction rates feasible for production. However, this high dilution may not be reliably ignited by the spark plug. These competing constraints demand novel mixture preparation strategies for SACI to be feasible in production. SACI with charge stratification has demonstrated sufficiently stable flame propagation to reliably trigger autoignition across much of the engine operating map. A key controls challenge of SACI is the two regimes of combustion are near several constraints that may be competing. This work summarizes key findings from decades of research that can help enable production control strategies for SACI engines. A summary and analysis of the broad research of SACI is included, along with an examination of the relevant factors that must be considered while developing a control strategy. Additionally, a discussion of how production-intent SACI designs extend or innovate upon previous decades of research is included. Key control actuators and design parameters are synthesized along with their sensitivity on several SACI combustion metrics.