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

Method for monitoring injection of a reductant into an exhaust gas feedstream upstream of an ammonia-selective catalytic reduction device, comprising:

• commanding a reductant dispensing device to dispense reductant at a prescribed reductant flowrate ({dot over (U)}C)from a supply of pressurized reductant to achieve a stoichiometric ratio of reductant to NOx in the exhaust gas feedstream upstream of the selective catalytic reduction device;
• providing a control signal to a reductant delivery system to establish the supply of pressurized reductant at a desired pressure;
• monitoring fluidic pressure in the reductant delivery system;
• determining a ratio of an estimated reductant flowrate out of a reductant pump ( {dot over (U)}a) of the reductant delivery system and the prescribed reductant flowrate ({dot over (U)}C) corresponding to the desired fluidic pressure and the monitored fluidic pressure;
• and
• diagnosing operation of the reductant injection system based upon the prescribed reductant flowrate ({dot over (U)}C) and the estimated reductant flowrate out of the reductant pump ({dot over (U)}a).

A reductant injection system, comprising:

• a reductant dispensing device receiving a supply of pressurized reductant;
• a control module commanding the reductant dispensing device to dispense reductant at a prescribed reductant flowrate ({dot over (U)}C)from the supply of pressurized reductant to achieve a stoichiometric ratio of reductant to NOx in the exhaust gas feedstream upstream of an ammonia-selective catalytic reduction device;
• a reductant delivery system including a motor driving a reductant pump to establish the supply of pressurized reductant;
• a control module providing a control signal to control the motor driving the reductant pump to establish the supply of pressurized reductant at a desired pressure;
• and
• a control module monitoring fluidic pressure in the reductant delivery system, determining a ratio of an estimated reductant flowrate out of the reductant pump ({dot over (U)}a) and the prescribed reductant flowrate ({dot over (U)}C) corresponding to the desired fluidic pressure and the monitored fluidic pressure, determining the reductant flowrate out of the reductant pump ({dot over (U)}a) based upon the prescribed reductant flowrate ({dot over (U)}a) and the ratio of the estimated reductant flowrate out of the reductant pump ({dot over (U)}a) and the prescribed reductant flowrate ({dot over (U)}C), and diagnosing operation of the reductant injection system based upon the prescribed reductant flowrate ({dot over (U)}C) and the estimated reductant flowrate out of the reductant pump ({dot over (U)}a).