System and method to control selective catalytic reduction systems in feedback

A system, comprising:

• an engine producing an exhaust stream as a byproduct of operation;
• an SCR catalyst component having a mid-bed position between two segments of SCR catalyst, the SCR catalyst component positioned to receive at least a portion of the exhaust stream;
• a mid-bed NOx sensor that provides a current mid-bed NOx amount, and a mid-bed NH3 sensor that provides a mid-bed NH3 amount, each of the mid-bed sensors operationally coupled to the exhaust stream at the mid-bed position;
• a controller, comprising:
• a system conditions module structured to interpret the current mid-bed NOx amount, the current mid-bed NH3 amount, and a current mid-bed ANR;
• a NOx modeling module structured to determine a feedforward mid-bed NOx target and a mid-bed ANR constraint;
• a NOx control module structured to provide an ANR command in response to the feedforward mid-bed NOx target;
• and
• a reductant injector operatively coupled to a reductant source and to the exhaust stream at a position upstream of the SCR catalyst component, wherein the reductant injector is responsive to the ANR command.

A method, comprising:

• determining a current mid-bed NH3 amount, the determining the mid-bed NH3 amount including operating an NH3 sensor positioned at a mid-bed location for an engine aftertreatment system having at least two SCR catalyst beds;
• operating a NOx sensor positioned at the mid-bed location;
• interpreting a current mid-bed ANR and a current mid-bed NOx in response to the mid-bed NH3 amount and the operating the NOx sensor, the interpreting the current mid-bed ANR and a current mid-bed NOx further including correcting an output value of the NOx sensor for cross-sensitivity to NH3;
• determining a mid-bed ammonia to NOx ratio (ANR) constraint;
• determining a feedforward mid-bed NOx target;
• and
• in response to the current mid-bed ANR, the current mid-bed NOx, the ANR constraint, and the feedforward mid-bed NOx target, providing a reductant injector command.

A system, comprising:

• an engine producing an exhaust stream as a byproduct of operation;
• an SCR catalyst component having a mid-bed position between two segments of SCR catalyst, the SCR catalyst component positioned to receive at least a portion of the exhaust stream;
• a mid-bed NOx sensor that provides a current mid-bed NOx amount, and a mid-bed NH3 sensor that provides a mid-bed NH3 amount, each of the mid-bed sensors operationally coupled to the exhaust stream at the mid-bed position;
• a reductant injector operatively coupled to a reductant source and to the exhaust stream at a position upstream of the SCR catalyst component;
• a means for determining a mid-bed NOx target in response to the mid-bed NOx amount and the mid-bed NH3 amount;
• and
• a means for controlling the reductant injector in response to the mid-bed NOx target.