Heating procedure for an exhaust catalyst of a lean Otto-engine with direct injection

Intake air is unthrottled during part load operation and dependent upon engine parameters. The fuel volume in a second fuel injection resp. after-injection, is regulated/controlled dependent upon intake air throttling in such a way, that a global Lambda area of 1,0 - 1,5 is maintained. Exhaust gas is returned via a unit for further reduction of the combustion speed of the lean burn mixture. Ignition is adjusted to 'late' between 30 degrees crankshaft angle before upper dead center and 15 degrees after upper dead center.