Patent ID: 8387448

Claim:
A method for monitoring performance of a passive selective catalytic reduction system configured to treat an exhaust gas feedstream from an internal combustion engine, the passive selective catalytic reduction system including a three-way catalytic device fluidly coupled upstream of a selective catalytic reduction catalyst, the method comprising: operating the internal combustion engine in a preconditioning mode; and then introducing an air/fuel excursion into the exhaust gas feedstream and monitoring a signal output from a sensor monitoring the exhaust gas feedstream in the passive selective catalytic reduction system during the air/fuel excursion; and determining an operating effectiveness for the passive selective catalytic reduction system correlated to the signal output from the sensor monitoring the exhaust gas feedstream, comprising: determining an operating effectiveness for the three-way catalytic device correlated to the signal output from the sensor monitoring the exhaust gas feedstream subsequent to introducing the air/fuel excursion; and determining an operating effectiveness for the selective catalytic reduction catalyst correlated to the signal output from the sensor monitoring the exhaust gas feedstream subsequent to introducing the air/fuel excursion.