Ion Current During the Exhaust Process Under the Idling Condition in a Spark Ignition Engine

Recently, in order to warm up the catalyst temperature rapidly, the retard ignition management has been developed. However, the excess retard of ignition causes the combustion instability and misfire. In this case, the ion sensor has been used for detecting the combustion quality for the late burned cycle under the idling condition. Several researchers have focused on the potential of ion-current measurement for the retard ignition management. However, the interpretation of ion-current during the exhaust process under the idling condition is not clear. In this study the source of ion-current for the late burned cycle during the exhaust process is focused. In order to measure the flame propagation process in the cylinder and the exhaust pipe, the single-cylinder test engine was used instead of production engine. Several ion probes were mounted on the cylinder head gasket, the piston head and the exhaust pipe for detecting the flame front. There are significant signals in the spark ion current, the gasket ion current and the piston ion current after the exhaust valve is opened for partial burn cycle. Then the flame area which contacts the chamber wall and the exhaust pipe, and the ion density control the waveforms of ion current obtained from the spark plug. In order to investigate the correlation between the combustion quality and the ion current obtained from the spark plug, two characteristic values of ion current for partial burn cycle were defined. Detecting the occurrence time of ion current and the integral value of ion current during exhaust process are useful for distinguishing the combustion quality under partial burn condition. The findings obtained from this paper are useful for analyzing the signal for late burned cycles under idling conditions when the retard ignition management is applied.