Aftertreatment catalyst degradation compensation

Abstract

One embodiment is a method including providing an aftertreatment catalyst disposed in an exhaust stream of an internal combustion engine and a reductant that reacts with an amount of NOx in the exhaust stream in the presence of the aftertreatment catalyst. The method includes interpreting a catalyst degradation value corresponding to the aftertreatment catalyst, and interpreting a nominal reductant value. The method further includes determining an adjusted reductant value in response to the catalyst degradation value and the nominal reductant value, and injecting the reductant into the exhaust stream at a rate based on the adjusted reductant value.

What is claimed is: 
     
         1 . A method, comprising:
 providing an aftertreatment catalyst disposed in an exhaust stream of an internal combustion engine;   providing a reductant that reacts with an amount of NO x  in the exhaust stream in the presence of the aftertreatment catalyst;   interpreting a catalyst degradation value corresponding to the aftertreatment catalyst;   interpreting a nominal reductant value;   determining an adjusted reductant value in response to the catalyst degradation value and the nominal reductant value; and   injecting the reductant into the exhaust stream at a rate based on the adjusted reductant value.   
     
     
         2 . The method of  claim 1 , wherein the reductant comprises a reductant selected from the group consisting of urea, ammonia, and a hydrocarbon. 
     
     
         3 . The method of  claim 1 , wherein the catalyst degradation value comprises at least one value selected from the values consisting of a NO x  conversion efficiency value and a reductant storage value. 
     
     
         4 . The method of  claim 3 , wherein the catalyst degradation value further comprises a function of a temperature of the aftertreatment catalyst. 
     
     
         5 . The method of  claim 3 , wherein the catalyst degradation value further comprises a function of a space velocity of the exhaust stream in the aftertreatment catalyst. 
     
     
         6 . The method of  claim 1 , wherein the nominal reductant value comprises a molar ratio of the reductant to the amount of NO x . 
     
     
         7 . The method of  claim 1 , wherein:
 the catalyst degradation value comprises at least one value selected from the values consisting of a NO x  conversion efficiency value and a reductant storage value;   the catalyst degradation value further comprises a function of a temperature of the aftertreatment catalyst and a space velocity of the exhaust stream in the aftertreatment catalyst;   wherein the interpreting a nominal reductant value comprises determining a nominal reductant to NO x  ratio; and   wherein the determining an adjusted reductant value comprises determining an adjusted reductant to NO x  ratio.   
     
     
         8 . The method of  claim 1 , wherein:
 the catalyst degradation value comprises at least one value selected from the values consisting of a NO x  conversion efficiency value and a reductant storage value;   the catalyst degradation value further comprises a function of a temperature of the aftertreatment catalyst;   wherein the interpreting a nominal reductant value comprises determining a nominal reductant to NO x  ratio; and   wherein the determining an adjusted reductant value comprises determining an adjusted reductant to NO x  ratio.   
     
     
         9 . The method of  claim 8 , wherein the adjusted reductant value comprises a value between 0.5 and 1.6, inclusive. 
     
     
         10 . The method of  claim 8 , wherein the adjusted reductant value comprises a value greater than 0.3, inclusive. 
     
     
         11 . The method of  claim 8 , wherein the adjusted reductant value comprises a value less than 3, inclusive. 
     
     
         12 . The method of  claim 8 , wherein the adjusted reductant value comprises a value less than 5, inclusive. 
     
     
         13 . A system, comprising:
 an aftertreatment catalyst disposed in an exhaust stream of an internal combustion engine;   a reductant that reacts with an amount of NO x  in the exhaust stream in the presence of the aftertreatment catalyst;   an injector structured to inject the reductant into the exhaust stream at a position upstream of the aftertreatment catalyst;   a degradation module structured to interpret a catalyst degradation value corresponding to the aftertreatment catalyst;   an injection amount module structured to interpret a nominal reductant value comprising a nominal reductant to NO x  ratio;   a degradation compensation module structured to determine an adjusted reductant value in response to the catalyst degradation value and the nominal reductant value; and   an injection control module structured to provide an injection rate signal based on the adjusted reductant value; and   an injector structured to inject the reductant into the exhaust stream at a position upstream of the aftertreatment catalyst in response to the injection rate signal.   
     
     
         14 . The system of  claim 13 , wherein the catalyst degradation value comprises at least one value selected from the values consisting of a NOx conversion efficiency value and a reductant storage value. 
     
     
         15 . The system of  claim 14 , wherein the catalyst degradation value further comprises a function of a temperature of the aftertreatment catalyst. 
     
     
         16 . The system of  claim 14 , wherein the catalyst degradation value further comprises a function of a space velocity of the exhaust stream in the aftertreatment catalyst. 
     
     
         17 . The system of  claim 13 , wherein the degradation module is further structured to define a first compensation region, a second compensation region, and an efficient catalyst region on a space-velocity temperature map in response to the catalyst degradation value, and wherein the degradation compensation module is further structured to:
 determine the adjusted reductant value as a value higher than the nominal reductant value in the first compensation region; and   determine the adjusted reductant value as a value lower than the nominal reductant value in the second compensation region.   
     
     
         18 . The system of  claim 13 , wherein the degradation compensation module is further structured to determine the adjusted reductant value according to one of the determination schemes selected from the schemes consisting of:
 determining an adjusted reductant value that provides a NO x  reduction amount achievable by a non-degraded catalyst with the nominal reductant value;   determining an adjusted reductant value that provides a NO x  reduction amount achievable by a non-degraded catalyst with the nominal reductant value limited by an ammonia slip amount;   determining an adjusted reductant value that provides at least a minimum NO x  reduction amount; and   determining an adjusted reductant value that does not exceed an ammonia slip amount.   
     
     
         19 . An apparatus, comprising:
 a degradation module structured to interpret a catalyst degradation value corresponding to an aftertreatment catalyst;   an injection amount module structured to interpret a nominal reductant value comprising a nominal reductant to NO x  ratio;   a degradation compensation module structured to determine an adjusted reductant value in response to the catalyst degradation value and the nominal reductant value; and   an injection control module structured to provide an injection rate signal based on the adjusted reductant value.   
     
     
         20 . The apparatus of  claim 19 , wherein the degradation module is further structured to define a first compensation region, a second compensation region, and an efficient catalyst region on a space-velocity temperature map in response to the catalyst degradation value, and wherein the degradation compensation module is further structured to:
 determine the adjusted reductant value as a value higher than the nominal reductant value in the first compensation region; and   determine the adjusted reductant value as a value lower than the nominal reductant value in the second compensation region.   
     
     
         21 . The apparatus of  claim 19 , wherein the degradation compensation module is further structured to determine the adjusted reductant value according to one of the determination schemes selected from the schemes consisting of:
 determining an adjusted reductant value that provides a NO x  reduction amount achievable by a non-degraded catalyst with the nominal reductant value;   determining an adjusted reductant value that provides a NO x  reduction amount achievable by a non-degraded catalyst with the nominal reductant value limited by an ammonia slip amount;   determining an adjusted reductant value that provides at least a minimum NO x  reduction amount; and   determining an adjusted reductant value that does not exceed an ammonia slip amount.   
     
     
         22 . A method, comprising:
 interpreting a catalyst degradation value corresponding to an aftertreatment catalyst;   interpreting a nominal reductant value comprising a nominal reductant to NO x  ratio;   determining an adjusted reductant value in response to the catalyst degradation value and the nominal reductant value;   providing an injection rate signal based on the adjusted reductant value; and   injecting an amount of reductant into an exhaust stream in response to the injection rate signal.   
     
     
         23 . The method of  claim 22 , wherein determining the adjusted reductant value comprises determining an adjusted reductant value that provides a NO x  reduction amount achievable by a non-degraded catalyst with the nominal reductant value. 
     
     
         24 . The method of  claim 22 , wherein determining the adjusted reductant value comprises determining an adjusted reductant value that provides a NO x  reduction amount achievable by a non-degraded catalyst with the nominal reductant value limited by an ammonia slip amount. 
     
     
         25 . The method of  claim 22 , wherein determining the adjusted reductant value comprises determining an adjusted reductant value that provides at least a minimum NO x  reduction amount. 
     
     
         26 . The method of  claim 22 , wherein determining the adjusted reductant value comprises determining an adjusted reductant value that does not exceed an ammonia slip amount.