Highly efficient conversion of nitrogen oxides in exhaust aftertreatment at low temperatures

摘要

A system and method for delivering reductant to a lean NOx catalyst receiving exhaust gases from an internal combustion engine operating at a lean air-fuel ratio in disclosed. Reductant supply is based on an amount of reductant stored within the catalyst. Furthermore, reductant is supplied under prescribed conditions including an exhaust gas concentration upstream of the catalyst of less than 25 ppm NOx or the catalyst at a temperature greater than 300° C.