Transient combustion timing management in controlled auto-ignition engine based on ion current signal

This study investigates the effects of mixture stratification on ion current signal from combustion chamber of controlled auto-ignition (CAI) engine fueled with gasoline. The CAI combustion mode was achieved by application of exhaust gas retention obtained via negative valve overlap. Split direct fuel injection technique was applied to achieve different degrees of fuel stratification, maintaining constant global mixture composition. As expected, mixture distribution within combustion chamber had strong effect on levels of recorded ion current. The aim of the study was verification of possibilities of using ion current measurements for transient control of combustion timing. It was yielded by analysis of characteristic phases of heat release rate and ion current signal. Correlations of combustion timing derived from in-cylinder pressure analysis and ion-current proved applicability of this measurement technique for CAI combustion control.