Optimization of ammonia dosing during regeneration

Abstract

A method for managing ammonia dosing during a regeneration event for a nitrogen oxide particulate filter in (NPF) includes a selective catalytic reduction system and a particulate filter. Embodiments include utilizing monitored pressure changes across the NPF to predict the soot load and when the soot load will reach a level that triggers a regeneration event. The predicted timing of the regeneration event is used to utilize ammonia absorbed on the NPF and adjust the amount or rate of dosing ammonia to manage ammonia levels in the NPF during the regeneration event. Prior to the regeneration event, the amount of dosing ammonia may be reduced so that ammonia released from the NPF is utilized in converting nitrogen oxides to nitrogen gas and water. After the released ammonia has been utilized, the amount of dosing ammonia may be increased so that the conversion of the nitrogen oxides continues.

1 . A method for managing an ammonia dosing strategy for the conversion of nitrogen oxides in a nitrogen oxide particulate filter that includes a selective catalytic reduction system and particulate filter for a combustion engine, the method comprising:
 monitoring a change in pressure across at least a portion of the nitrogen oxide particulate filter;   predicting when a regeneration event within the nitrogen oxide particulate filter will be initiated based on the monitored change in pressure across the nitrogen oxide particulate filter; and   adjusting the amount of dosing ammonia provided to the nitrogen oxide particulate filter when the regeneration event is predicted to be initiated.   
     
     
         2 . The method of  claim 1 , further comprising determining a soot load within the nitrogen oxide particulate filter based on the monitored changed in pressure. 
     
     
         3 . The method of  claim 2 , wherein the step of determining when the regeneration event will be initiated includes determining when the soot load in the nitrogen oxide particulate filter will reach a predetermined level. 
     
     
         4 . The method of  claim 1 , further comprising manipulating operation of the combustion engine to reduce the amount of nitrogen oxide produced by the combustion engine during the regeneration event. 
     
     
         5 . The method of  claim 1 , wherein the step of adjusting the amount of dosing ammonia includes reducing the amount of dosing ammonia present in the nitrogen oxide particulate filter in advance of the predicted regeneration event so that ammonia released from the nitrogen oxide particulate filter is utilized for the conversion of nitrogen oxides in the selective catalytic reduction system. 
     
     
         6 . The method of  claim 5 , wherein the step of adjusting the amount of dosing ammonia further includes increasing the amount of dosing ammonia present in the nitrogen oxide particulate filter after the released ammonia that was stored in the nitrogen oxide particulate filter has been at least partially depleted through the conversion of nitrogen oxides in the selective catalytic reduction system. 
     
     
         7 . A method for managing an ammonia dosing strategy for the conversion of nitrogen oxides in a nitrogen oxide particulate filter that includes a selective catalytic reduction system and particulate filter for a combustion engine, the method comprising:
 monitoring a change in pressure across at least a portion of the nitrogen oxide particulate filter;   predicting a soot load level in the nitrogen oxide particulate filter using the monitored change in pressure across the nitrogen oxide particulate filter;   predicting when the predicted soot load level will reach a predetermine level that will trigger a regeneration event;   reducing the amount of dosing ammonia provided to the nitrogen oxide particulate filter in advance of the regeneration event to prevent the accumulation of excess ammonia in the nitrogen oxide particulate filter during the regeneration event; and   releasing ammonia stored on the nitrogen oxide particulate filter, the released ammonia being used in the conversion of the nitrogen oxides in the selective catalytic reduction system.   
     
     
         8 . The method claim of  claim 7 , further including increasing the amount of dosing ammonia after the released ammonia has been depleted by the conversion of nitrogen oxides in the selective catalytic reduction system. 
     
     
         9 . The method of  claim 8 , wherein the amount of dosing ammonia is increased in advance of the regeneration event. 
     
     
         10 . The method of  claim 8 , wherein the amount of dosing ammonia is increased during the regeneration event. 
     
     
         11 . The method of  claim 7 , further comprising manipulating operation of the combustion engine to reduce the amount of nitrogen oxide produced by the combustion engine during the regeneration event. 
     
     
         12 . A method for managing an ammonia dosing strategy for the conversion of nitrogen oxides in a nitrogen oxide particulate filter that includes a selective catalytic reduction system and particulate filter for a combustion engine, the method comprising:
 predicting when a regeneration event within the nitrogen oxide particulate filter will be initiated, the regeneration event configured to combust soot that has accumulated in the nitrogen oxide particulate filter;   releasing ammonia stored in the nitrogen oxide particulate filter in advance of the regeneration event, the released ammonia being used in the selective catalytic reduction system for the conversion of nitrogen oxides;   decreasing the amount of reductant injected into the exhaust gas entering the nitrogen oxide particulate filter while the released ammonia is being used in the conversion of nitrogen oxides in the selective reduction system; and   increasing the amount of reductant injected into the exhaust gas after the released ammonia has been at least partially depleted to continue the conversion of nitrogen oxides in the selective reduction system.   
     
     
         13 . The method of  claim 12 , wherein the step of predicting when the regeneration event will be initiation includes monitoring changes in pressure across the nitrogen oxide particulate filter. 
     
     
         14 . The method of  claim 13 , wherein the monitored pressure changes and predicted soot load are used to predict when the soot level will reach a predetermined triggering level. 
     
     
         15 . The method of  claim 12 , further comprising manipulating operation of the combustion engine to reduce the amount of nitrogen oxide produced by the combustion engine during the regeneration event.