Method for managing ammonia slip

Method for operating an internal combustion engine including an exhaust aftertreatment system comprising an ammonia-selective catalytic reduction device, the method comprising:

• monitoring engine operation;
• determining a present engine NOx generation rate corresponding to the monitored engine operation;
• determining an actual NOx reduction rate of the ammonia-selective catalytic reduction device;
• determining a rate of ammonia slip output from the ammonia-selective catalytic reduction device based upon a difference between the actual NOx reduction rate and the present engine NOx generation rate;
• and
• adjusting, by a controller, the engine NOx generation rate in response to the rate of ammonia slip output from the ammonia-selective catalytic reduction device, comprising:
• determining an actual ammonia storage trajectory for the ammonia-selective catalytic reduction device corresponding to the present engine NOx generation rate,
• adjusting the present engine NOx generation rate to achieve a preferred ammonia storage trajectory associated with a setpoint amount of stored ammonia to prevent said ammonia slip, the setpoint amount of stored ammonia determined in relation to an inlet temperature of the ammonia-selective catalytic reduction device,
• employing an inverse engine NOx generation model to determine a fraction of externally recirculated exhaust gas that achieves the adjusted engine NOx generation rate, and
• controlling a flowrate of the externally recirculated exhaust gas to achieve the fraction of externally recirculated exhaust gas that achieves the adjusted engine NOx generation rate.

Method for operating an internal combustion engine coupled to an exhaust aftertreatment system consisting of a three-way catalytic converter and an ammonia-selective catalytic reduction device, the method comprising:

• determining a NOx reduction rate in the ammonia-selective catalytic reduction device;
• determining an ammonia slip rate from the ammonia-selective catalytic reduction device corresponding to the NOx reduction rate of the ammonia-selective catalytic reduction device;
• and
• controlling, by a controller, an engine NOx generation rate in response to the ammonia slip rate from the ammonia-selective catalytic reduction device, comprising:
• determining an actual ammonia storage trajectory for the ammonia-selective catalytic reduction device corresponding to a present engine NOx generation rate,
• adjusting the present engine NOx generation rate to achieve a preferred ammonia storage trajectory associated with a setpoint amount of stored ammonia to prevent said ammonia slip, the setpoint amount of stored ammonia determined in relation to an inlet temperature of the ammonia-selective catalytic reduction device,
• employing an inverse engine NOx generation model to determine a fraction of externally recirculated exhaust gas that achieves the adjusted engine NOx generation rate, and
• controlling flow of the externally recirculated exhaust gas to the engine to achieve the fraction of externally recirculated exhaust gas that achieves the adjusted engine NOx generation rate.