Method and apparatus for monitoring a urea injection system in an exhaust aftertreatment system

Monitoring system for an exhaust aftertreatment system comprising an injecting device operable to inject reductant into an exhaust gas feedstream upstream of a selective catalyst reduction device, comprising:

• a control module, adapted to:
• determine a stoichiometric reductant/NOx ratio;
• control a rate of reductant dosing from the injecting device to a non-stoichiometric reductant/NOx dosing rate;
• monitor inputs from a sensing device that monitors the exhaust gas feedstream subsequent to passing though at least a portion of the selective catalytic reduction device, and,
• detect a fault in the exhaust aftertreatment system based upon the monitored inputs solely from the sensing device subsequent to controlling the rate of reductant dosing from the injecting device to the non-stoichiometric reductant/NOx dosing rate.

Monitoring system for an exhaust aftertreatment system comprising an injecting device operable to inject reductant into an exhaust gas feedstream upstream of a selective catalyst reduction device, comprising:

• a control module, adapted to:
• control a rate of reductant dosing from the injecting device;
• monitor inputs from a sensing device operative to monitor the selective catalyst reduction device;
• determine a closed loop correction factor to control the rate of reductant dosing from the injecting device based upon the monitored signal inputs from the sensing device;
• monitor refilling events of a reductant storage tank;
• and,
• identify a fault in reductant quality when a change in the closed loop correction factor exceeds a threshold after a refilling event of the reductant storage tank.

Monitoring system for an exhaust aftertreatment system comprising an injecting device operable to inject reductant into an exhaust gas feedstream upstream of a selective catalyst reduction device, comprising:

• a control module, adapted to:
• control a rate of reductant dosing from the injecting device;
• monitor inputs from a sensing device operative to monitor the selective catalyst reduction device;
• determine a plurality of closed-loop correction factors to control the rate of reductant dosing by the injecting device, each closed-loop correction factor based upon the monitored signal inputs from the sensing device in an engine speed/load operating region;
• and,
• identify a fault in reductant quality when a change in one of the closed loop correction factors exceeds a predetermined threshold for the engine speed/load operating region.