METHOD FOR OPERATING A SPARK IGNITED ENGINE

A method includes forming a combustible mixture by mixing generally homogeneously a first fuel and air and introducing this mixture into a cylinder, compressing the combustible mixture with a piston in a compression stroke, introducing a second fuel into a prechamber at an introduction-time before start of combustion thus creating a prechamber charge, in which the second fuel being of the same or different chemical composition and/or concentration with respect to the first fuel, and spark igniting the prechamber charge. Emission of the cylinder and/or mechanical stress of the cylinder caused by the combustion are monitored. If emissions and/or mechanical stress are above respective predetermined thresholds, individually for the at least one cylinder, the chemical composition and/or the amount of second fuel introduced into the prechamber, and/or temperature of the cylinder charge and/or spark timing , are changed.