Patent ID: 8448423

Claim:
Method for operating a multi-cylinder, spark-ignition, direct-injection, internal combustion engine having an exhaust outlet providing an exhaust gas feedstream fluidly connected to an exhaust aftertreatment system comprising a particulate filter device upstream of a first aftertreatment device fluidly connected upstream of a second aftertreatment device, the first aftertreatment device comprising an oxidation catalytic device, wherein the particulate filter device and the oxygen catalytic device are closely coupled to the exhaust outlet and the second aftertreatment device comprising a selective catalyst reduction device having a capacity to store an ammonia reductant, the method comprising: detecting a start and run event for the engine; and then initially controlling the engine at a stoichiometric air/fuel ratio using a multiple pulse fuel injection strategy wherein a portion of the fuel is injected late in the combustion cycle and retarding spark ignition timing relative to mean-best-torque timing for a period of time associated with achieving light-off temperature in the first aftertreatment device; and then controlling the engine at a lean air/fuel ratio using the multiple pulse fuel injection strategy wherein a portion of the fuel is injected late in the combustion cycle and retarding the spark ignition timing relative to mean-best-torque timing for a period of time associated with achieving an efficient NOx conversion rate in the second aftertreatment device; and then operating the engine at a lean air/fuel ratio and controlling spark ignition timing to a preferred timing; and then operating the engine in a first combustion mode comprising operating at a rich air/fuel ratio and advancing the spark ignition timing to generate reformates that form an ammonia reductant in the first aftertreatment device and storing the ammonia reductant on the second aftertreatment device until ammonia slip from the second aftertreatment device exceeds a predetermined level; and then operating the engine at a preferred air/fuel ratio and controlling spark ignition timing to a preferred timing until the stored ammonia reductant is depleted.