Patent ID: 7481039

Claim:
A method for controlling an engine having at least a first and second group of cylinders, comprising: operating the engine in a first mode wherein the first cylinder group operates with air and substantially no injected fuel and the second cylinder group operates to combust air and injected fuel; during a first condition, transitioning the engine to operating in a second mode wherein both the first cylinder group and the second cylinder group operate to combust air and injected fuel, combustion in both said first and second cylinder group being lean of stoichiometry at a lean combustion limit with retarded ignition timing; and during a second condition, transitioning the engine to operating in a third mode wherein both the first cylinder group and the second cylinder group operate to combust air and injected fuel, combustion in both said first and second cylinder group being lean of stoichiometry less lean than the lean combustion limit without retarded ignition timing.