A system and method controls auto-ignition of gasoline fuel within a cylinder of an internal combustion engine by varying an exhaust gas retaining duration. A generator provides a parameter indicative of combustion event within the cylinder. An engine controller adjusts an inlet control device and an outlet control device to retain exhaust gas for subjecting the retained exhaust gas to compression. In order to vary duration of the exhaust gas retaining phase, closing timing of the outlet control device is varied based on the parameter.