Exhaust system implementing in situ calibration

A method of operating a combustion engine, comprising:

• directing a flow of exhaust from the combustion engine through a reduction catalyst;
• determining an amount of NOX in the flow of exhaust upstream of the reduction catalyst;
• referencing a NOX/reductant relationship map to determine an initial amount of reductant that should be directed into the flow of exhaust based on the determined amount of NOX;
• determining a performance of the reduction catalyst;
• determining an adjusted amount of reductant based on the determined performance;
• directing the adjusted amount of reductant into the exhaust flow upstream of the reduction catalyst;
• and
• updating the NOX/reductant relationship map based on a difference between the initial amount of reductant and the adjusted amount of reductant, wherein updating includes periodically updating the NOX/reductant relationship map with time averaged values for the difference between the initial amount of reductant and the adjusted amount of reductant.

A power system, comprising:

• an engine configured to combust fuel and generate a flow of exhaust;
• an exhaust passageway leading from the engine to the atmosphere;
• an SCR catalyst disposed within the exhaust passageway;
• a first sensor located to generate a first signal indicative of a NOX production by the engine;
• a second sensor located downstream of the SCR catalyst to generate a second signal indicative of a residual amount of at least one of NOX and NH3;
• an injection device located to inject urea into the exhaust passageway upstream of the SCR catalyst;
• and
• a controller in communication with the engine, the first sensor, the second sensor, and the injection device, the controller being configured to:
• reference a NOX/urea relationship map to determine an initial amount of urea that should be directed into the exhaust passageway based on the first signal;
• reference a residual gas/urea relationship map to determine an adjustment to the initial amount of urea based on the second signal;
• regulate operation of the urea injector to direct an adjusted amount of urea into the exhaust passageway;
• periodically update the NOX/urea relationship map with time averaged values from the residual gas/urea relationship map;
• and
• periodically update the residual gas/urea relationship map with time averaged values from the second sensor.