System and method for injection control of urea in selective catalyst reduction

A system, comprising:

• an exhaust aftertreatment system configured to treat emissions from a combustion engine, wherein the exhaust aftertreatment system comprises:
• a selective catalytic reduction (SCR) catalyst assembly configured to receive a fluid from the combustion engine, wherein the SCR catalyst assembly has an inlet and an outlet;
• at least one radio frequency (RF) probe disposed within the SCR catalyst and configured to measure ammonia (NH3) storage of the SCR catalyst;
• an injection system configured to inject NH3 or urea into the fluid upstream of the inlet of the SCR catalyst;
• a controller communicatively coupled to the exhaust aftertreatment system, wherein the controller is configured to control operations of the exhaust aftertreatment system and to receive signals representative of the measured concentrations of nitrogen oxides (NOx) or NH3 in the fluid upstream of the SCR catalyst, to receive signals representative of the measured concentrations of NOx or NH3 in the fluid downstream of the SCR catalyst, or any combination thereof;
• and a signal representative of the NH3 storage measurement from the at least one RF probe;
• and
• an NH3 storage estimate model configured to determine an NH3 storage estimate based on at least the signals representative of the measured concentrations of NOx or NH3 in the fluid upstream of the SCR catalyst or the signals representative of the measured concentrations of NOx or NH3 in the fluid downstream of the SCR catalyst, or any combination thereof;
• wherein the controller is configured to utilize at least both the estimated NH3 storage estimate and the NH3 storage measurement to output a control action for the injection system.