INTERACTION OF FLAME PROPAGATION AND PRESSURE WAVES DURING KNOCKING COMBUSTION IN SPARK-IGNITION ENGINES

Knocking combustion in spark-ignition (SI) engines is a typical abnormal combustion phenomenon that severely limits engine performance and thermal efficiency. However, its mechanism has not so far been completely revealed, such as the origin of pressure oscillation with tremendous amplitude and broken mechanisms of the engine body when knock occurs. This article systematically reviews the series of physical and chemical phenomena involved in knocking combustion, including auto-ignition, gas-dynamic waves, cavity resonance, and auto-ignited flame propagation. Significant research has shown that the rapid heat release of end-gas auto-ignition and subsequent strong pressure waves play a crucial role during knocking combustion. A methodology of the interaction of flame propagation and pressure waves has been proposed to reveal knock formation in terms of positive feedback between strengthened pressure waves and auto-ignited flame propagation. Also, new suggestions on the weakness in prior research of knocking combustion have also been discussed in the present article.