Pre-ignition-prevention control method in spark-ignition engines by detecting precursory cycles with an ion-current sensor

Abstract

In gasoline engines with a higher compression ratio, abnormal combustion, such as pre-ignition and knocking, tends to occur due to higher temperature in the combustion chamber, which leads to lower engine performance. To prevent pre-ignition from occurring, we propose a pre-ignition-prevention control method that involves using an ion-current sensor integrated in an ignition system. The pre-ignition and precursory cycles are detected from the ion-current intensity and spark-discharge duration estimated from ion-current signals. Fuel-injection is increased to cool the mixture in the combustion chamber after the abnormal combustion (precursory) cycle is detected. In a commercial gasoline engine, it was demonstrated that our method can prevent pre-ignition combustion by setting a proper threshold for precursory-cycle detection. The effectiveness of the fuel-injection control was analyzed.