Patent ID: 8915062

Claim:
Method for monitoring a reductant injection system including a reductant delivery system fluidly coupled to a reductant dispensing device configured to dispense reductant into an exhaust gas feedstream of an internal combustion engine upstream of an ammonia-selective catalytic reduction device, comprising: commanding the reductant dispensing device to dispense reductant at a prescribed reductant flowrate ({dot over (U)} C ) that achieves a stoichiometric ratio of reductant to NOx in the exhaust gas feedstream upstream of the ammonia-selective catalytic reduction device; controlling the reductant delivery system to achieve a preferred operating state comprising a desired fluidic pressure in the reductant delivery system to dispense the reductant at the prescribed reductant flowrate ({dot over (U)} C ); monitoring fluidic pressure in the reductant delivery system; determining a ratio of an estimated reductant flowrate out of a reductant pump ( {dot over (U)} a ) and the prescribed reductant flowrate ({dot over (U)} C ) corresponding to the desired fluidic pressure and the monitored fluidic pressure; and diagnosing operation of the reductant injection system based upon the prescribed reductant flowrate {dot over (U)} C ) and the estimated reductant flowrate out of the reductant pump {dot over (U)} a ).