Emission control system

An engine exhaust aftertreatment system is described in which lean NOx exhaust aftertreatment devices are employed. Because temperature in the exhaust line (38) varies as a function of distance from the engine and engine operating condition, exhaust aftertreatment devices (20,26) are situated along the exhaust line to ensure that at least one of said exhaust aftertreatment devices operates at a temperature of high NOx conversion efficiency. Reductant quantity is scheduled by the engine's control unit (40) to be supplied to the exhaust aftertreatment devices (20,26) based on available information provided by sensors (16,24,30,32,34) or embedded engine control unit models, including: temperature in the exhaust aftertreatment devices (20,26), available reductant in the exhaust stream, reductant storage in the exhaust aftertreatment devices, maximum adsorption capacity of the exhaust aftertreatment devices, engine operating conditions, and NOx concentration.