Ion Sensing for Combustion Stability Control of a Spark Ignited Direct Injected Engine

The combustion stability of a direct injected spark ignited engine depends on the injection timing and it is desirable to have controller that minimizes the combustion variability.

A novel approach for determining combustion stability in stratified mode is presented that rely on the ionization current and enables closed loop control of the injection timing. The co-efficient of variation for IMEP is used as a measure of combustion stability and a connection between maximum torque and low combustion variability is pointed out. The coefficient of variation of the ion current integral is well correlated with the coefficient of variation for IMEP. Furthermore, it is shown how the integral of the ion current together with COV(ion integral) can be used to determine the combustion stability and to distinguish high combustion stability from misfire.