Experimental Investigation of Spark Assisted Auto-Ignition Combustion in a Small Two-Stroke Engine

The local temperature of the in-cylinder mixture before combustion is critical to enable auto-ignition (AI) in a gasoline engine. Spark assistance is one of the methods to ensure the critical temperature required for auto-ignition. The application of the spark gives a time controlled initiation to the onset of ignition. In the work reported in this paper, spark assisted AI was experimentally investigated on a small two-stroke engine. The spark assistance and internal exhaust gas recirculation (EGR) were jointly applied to achieve and control AI. The results showed that at higher engine load, the onset timing of AI had a clear dependence on the timing of the spark and was consistent from cycle to cycle. At lower engine load, the assistance of the spark became necessary for keeping the AI operation to continue.