Spark ignition internal combustion engine and control method of spark ignition internal combustion engine

Abstract

A spark ignition internal combustion engine includes an exhaust gas reflux device capable of refluxing exhaust gas having passed through a catalyst for exhaust gas purification to an intake passage, an ignition timing control means for setting an ignition timing retard amount capable of preventing knocking according to a NOx concentration in the exhaust gas while the exhaust gas is refluxed, a NOx concentration estimation means for estimating the NOx concentration in the exhaust gas, and a purification performance reduction determination means for determining a reduction in purification performance of the catalyst. The ignition timing control means sets the ignition timing retard amount based on the NOx concentration in the exhaust gas before passage through the catalyst if the purification performance reduction determination means determines that the purification performance of the catalyst has been reduced to a state set in advance.