Catalyst failure detection based combined ammonia to NOx ratios, conversion inefficiency values and ammonia slip values

A controller comprising:

• an ammonia to NOx ratio (ANR) circuit configured to determine an ANR value for an exhaust system including a selective catalytic reduction (SCR) catalyst;
• a deNOx conversion inefficiency circuit configured to calculate a conversion inefficiency value based on an actual conversion efficiency for the SCR catalyst and an estimated target conversion efficiency for the SCR catalyst;
• a NH3 slip circuit configured to determine an NH3 slip value for the exhaust system;
• and
• a combined ANR/conversion inefficiency/NH3 slip (ACN) circuit configured to:
• receive the NH3 slip value from the NH3 slip circuit, the ANR value from the ANR circuit, and the conversion inefficiency value from the deNOx conversion inefficiency circuit,
• determine an ACN value based on the NH3 slip value, the ANR value, and the conversion inefficiency value,
• compare the determined ACN value to a predetermined threshold value, and
• indicate a failure of the SCR catalyst responsive to the determined ACN value exceeding a predetermined threshold value.

A method for indicating a failure of a selective catalytic reduction (SCR) catalyst of an exhaust system, the method comprising:

• acquiring an ammonia to NOx ratio (ANR) value for exhaust gas flowing through the exhaust system;
• acquiring a conversion inefficiency value indicative of a conversion inefficiency of the SCR catalyst;
• acquiring an NH3 slip value indicative of an amount of NH3 slip through the exhaust system downstream of the SCR catalyst;
• calculating a combined ANR/conversion inefficiency/NH3 slip (ACN) value based on the acquired ANR value, the acquired conversion inefficiency value, and the acquired NH3 slip value;
• and
• indicating a failure of the SCR catalyst responsive to the calculated ACN value exceeding a predetermined threshold value.