Using an ion-current sensor integrated in the ignition system to detect precursory phenomenon of pre-ignition in gasoline engines

To enhance the thermal efficiency, compression ratio in recent gasoline engines is becoming higher. In these engines, pre-ignition tends to occur due to higher temperature in the combustion chamber, that leads to lower engine performance and engine damage eventually. In order to detect pre-ignition and its precursory phenomenon, an ion-current sensor integrated in the ignition system is applied. Firstly, through the combustion analysis during the transition phase from normal combustion to pre-ignition cycles, the combustion characteristics of precursory cycles are identified in actual gasoline engine with high compression ratio. Next, a method for detecting pre-ignition and its precursory phenomenon by using ion-current sensor is considered. Although the pre-ignition cycle can be distinguished from normal cycles by simply using an integral value of the ion-signal intensity as an indicator, the precursory cycle cannot be identified clearly because the ion-current sensor cannot work during the spark ignition phase. Considering this issue, a new method that utilizes the spark-discharge duration measured by the ion-current sensor is proposed, and it is demonstrated that this method can accurately identify the precursory cycle of pre-ignition. It has the potential to be utilized for robust detection and control for higher thermal efficiency in the practical engines.