| abstract |
Internal combustion engine (ICE) exhaust gas treatment systems include the ICE having one or more cylinders configured to receive a mixture of air and fuel defined by an air to fuel ratio (AFR) for combustion therein, a control module configured to control the AFR, a diesel oxidation catalyst (DOC) configured to receive exhaust gas generated by the ICE and oxidize NOx species within the exhaust gas, and a selective catalytic reduction device (SCR) configured to receive exhaust gas from the DOC. Methods for operating and diagnosing such systems include determining, via the control module, a baseline value of a SCR performance parameter which is unsuitable, changing, via the control module, the AFR to change the DOC outlet NO2:NOx ratio, subsequently assessing a second value of the SCR performance parameter, and implementing a control action based on the second value of the SCR performance parameter. |