System and methods for controlling selective catalytic reduction systems

A method, comprising:

• generating an aging factor based on an age of a catalyst in a selective catalytic reduction (SCR) system, wherein the age indicates an amount of deterioration of the catalyst in the SCR system;
• comparing inlet and outlet temperatures of the SCR system to predetermined effective inlet and outlet temperatures of the SCR system, respectively, wherein the predetermined effective inlet and outlet temperatures are based on the aging factor;
• and
• controlling at least one of a throttle and a plurality of fuel injectors based on a first predetermined air/fuel (A/F) ratio when the inlet and outlet temperatures of the SCR system are greater than the predetermined effective inlet and outlet temperatures of the SCR system, respectively.

A method for controlling an engine, the method comprising:

• determining a degree of deterioration of a selective catalytic reduction (SCR) catalyst configured to treat exhaust gas produced by the engine;
• determining a minimum effective inlet temperature of the SCR catalyst based on (i) an initial effective inlet temperature of the SCR catalyst when the SCR catalyst was new and (ii) the degree of deterioration;
• determining a minimum effective outlet temperature of the SCR catalyst based on (i) an initial effective outlet temperature of the SCR catalyst when the SCR catalyst was new and (ii) the degree of deterioration;
• monitoring an inlet temperature of the SCR catalyst using a first temperature sensor;
• monitoring an outlet temperature of the SCR catalyst using a second temperature sensor;
• commanding the engine to operate based on a first air/fuel ratio when at least one of the inlet temperature is less than the minimum effective inlet temperature and the outlet temperature is less than the minimum effective outlet temperature;
• and
• commanding the engine to operate based on a second air/fuel ratio when both the inlet temperature is greater than or equal to the minimum effective inlet temperature and the outlet temperature is greater than or equal to the minimum effective outlet temperature, wherein the first air/fuel ratio is less than the second air/fuel ratio.