Patent ID: 7485272

Claim:
A method of controlling nitric oxides emissions, comprising: producing an exhaust gas stream containing NOx; supplying the exhaust gas stream to an exhaust passage; producing a second exhaust gas stream containing NOx by combustion of a fuel within at least one engine cylinder and converting at least a portion of the NOx in the second exhaust gas stream into ammonia to produce an ammonia-containing exhaust gas stream; supplying the ammonia-containing exhaust gas stream to the exhaust passage at a location upstream of a first selective catalytic reduction catalyst, wherein the amount of ammonia supplied at the first location is less than about 90% of the effective amount of ammonia needed for reduction of all NOx at the first location; and supplying urea to the exhaust passage at a second location downstream of the first selective catalytic reduction catalyst and upstream of a second selective catalytic reduction catalyst.