HIGHLY EFFICIENT CONVERSION OF NITROGEN OXIDE IN EXHAUST AFTERTREATMENT DEVICE AT LOW TEMPERATURE

摘要

PROBLEM TO BE SOLVED: To activate lean NOx catalyst for treating lean exhaust emission at a high conversion efficiency in a temperature range lower than that allowed before. SOLUTION: In a system and a method, reducer is supplied to the lean NOx catalyst 30 receiving exhaust emission from an internal combustion engine 10 operating at a lean air/fuel ratio. The supplied amount of the reducer is determined based on the amount of the reducer occluded in the catalyst 30. The reducer is supplied under the predetermined conditions including that the NOx density of the exhaust emission on the upstream side of the catalyst 30 is less than 25 ppm or the temperature of the catalyst does not exceed 300 deg.C.