Retarding engine timing and adding air to exhaust system

摘要

A method for operating an engine with an emission control device in an exhaust system of the engine, and an air introduction device coupled to the exhaust system, comprises operating the engine in a first mode in which the engine timing is retarded from the optimal torque timing and the engine combusts a lean air-fuel mixture, and continuing said operating in the first mode until a first threshold is reached. After the first threshold is reached the engine is operated in a second mode in which the engine combusts a rich air-fuel mixture and air is added to the exhaust system via the air introduction device. The predetermined threshold may be a pre-selected exhaust system temperature. A second threshold may be determined above the first threshold, above which the engine operates in a third mode, wherein the engine is operated with a substantially stoichiometric air-fuel ratio.