Patent ID: 8857153

Claim:
An engine system, comprising: an engine including an exhaust passage; an ammonia injector positioned in the exhaust passage; a selective catalyst reaction (SCR) catalyst positioned downstream of the injector; a differential NOx and ammonia sensing device sensing exhaust gases upstream and downstream of the ammonia injector, the sensing device positioned upstream of the SCR, the sensing downstream of the ammonia injector is still upstream of the SCR; and a controller configured with a differential logic unit to determine the concentration of ammonia in the exhaust passage based on the sensed exhaust gases upstream and downstream of the ammonia injector, the controller further including instructions for adjusting engine operation in response to an output of the differential logic unit, including adjusting engine operation responsive to a deposition rate of ammonia in the exhaust passage calculated via a memory model, where adjusting engine operation increases an exhaust gas temperature to purge ammonia deposits in response to the deposition rate of ammonia calculated in the exhaust passage exceeding a threshold.