Selective catalytic reduction steady state ammonia slip detection

An exhaust system for treating exhaust gas emitted by an internal combustion engine, configured to perform a selective catalytic reduction (SCR) of exhaust gas, the exhaust system comprising:

• a controller configured to perform ammonia slip detection by:
• comparing an NOx measurement from an NOx sensor of the exhaust system with a predicted NOx value;
• and
• in response to the NOx measurement exceeding the predicted NOx value by a threshold value, the threshold value being calibrated to a first predetermined value:
• calibrating the threshold value to a second predetermined value;
• and
• initiating a timer of a predetermined duration, wherein during the predetermined duration of the timer:
• in response to a second NOx measurement from the NOx sensor exceeding the predicted NOx value by the threshold value set to the second predetermined value, adapting a reductant dosing rate for the SCR according to the second predetermined value;
• wherein the second predetermined value is less than or equal to 50% of the first predetermined value.

A computer-implemented method for controlling a selective catalytic reduction (SCR) device of an exhaust system of an internal combustion engine, the method comprising:

• performing ammonia slip detection by:
• comparing an NOx measurement from an NOx sensor of the SCR device with a predicted NOx value;
• and
• in response to the NOx measurement exceeding the predicted NOx value by a threshold value, the threshold value being calibrated to a first predetermined value:
• calibrating the threshold value to a second predetermined value;
• and
• initiating a timer of a predetermined duration, wherein during the predetermined duration of the timer:
• in response to a second NOx measurement from the NOx sensor exceeding the predicted NOx value by the threshold value set to the second predetermined value, adapting a reductant dosing rate of the SCR device according to the second predetermined value;
• wherein the second predetermined value is less than or equal to 50% of the first predetermined value.