Patent ID: 8004695

Claim:
A method for comparing a thickness of a film of a reductant for nitrogen oxides on an interior surface of an exhaust pipe system to exhaust pipe system conditions, wherein the exhaust pipe system comprises an exhaust pipe connected to an exhaust port of a nitrogen-oxides producing engine and a selective catalytic reduction injector configured to introduce a reductant solution of the reductant into the exhaust pipe, the method comprising: (a) measuring a first thickness of the film at a measurement location within the exhaust pipe system at a first measurement time; (b) introducing a reductant solution from the injector into the exhaust pipe during operation of the engine; (c) measuring a second thickness of the film at the measurement location at a second measurement time; (d) using a control unit to determine at least one exhaust pipe system condition, wherein the control unit comprises one or more computers, computing devices, microcontrollers, programmable logic controllers, or combinations thereof; and (e) using the control unit to compare the first thickness of the film and the second thickness of the film with the at least one exhaust pipe system condition between the first measurement time and the second measurement time.