Aftertreatment system

Abstract

An aftertreatment system for an internal combustion engine includes a treatment device having a combined particulate filter and SCR catalyst. The combined particulate filter and SCR catalyst treats uncatalyzed exhaust from the internal combustion engine including between approximately 7 g NOx/kW-hr and approximately 10 g NOx/kW-hr.

1 . An aftertreatment system for an internal combustion engine, comprising:
 a treatment device including a combined particulate filter and SCR catalyst, the combined particulate filter and SCR catalyst treating uncatalyzed exhaust from the internal combustion engine comprising between approximately 7 g NOx/kW-hr and approximately 10 g NOx/kW-hr.   
     
     
         2 . The aftertreatment system of  claim 1 , further comprising a reductant injector disposed upstream of the treatment device and configured to inject a reductant into the uncatalyzed exhaust. 
     
     
         3 . The aftertreatment system of  claim 2 , further comprising a mixing tube connected to an inlet of the treatment device, the reductant injector being fluidly connected to the mixing tube. 
     
     
         4 . The aftertreatment system of  claim 3 , further comprising a mixer disposed within the mixing tube. 
     
     
         5 . The aftertreatment system of  claim 1 , further comprising an additional catalyst disposed downstream of the combined particulate filter and SCR catalyst. 
     
     
         6 . The aftertreatment system of  claim 5 , wherein the additional catalyst comprises an SCR catalyst. 
     
     
         7 . The aftertreatment system of  claim 6 , wherein the additional catalyst further comprises one of an ammonia oxidation catalyst and a diesel oxidation catalyst. 
     
     
         8 . The aftertreatment system of  claim 5 , wherein the combined particulate filter and SCR catalyst and the additional catalyst are disposed within a single canister. 
     
     
         9 . An aftertreatment system for an internal combustion engine, comprising:
 a treatment device including a first SCR catalyst disposed on a particulate filter substrate, and a second SCR catalyst downstream of the first SCR catalyst, the first SCR catalyst treating uncatalyzed exhaust from the internal combustion engine, wherein the treatment device is characterized by a NOx conversion efficiency greater than approximately 95 percent.   
     
     
         10 . The aftertreatment system of  claim 9 , wherein the first and second SCR catalysts are disposed within a single canister, the canister including at least one removable end portion configured to provide access to at least one of the first and second SCR catalysts. 
     
     
         11 . The aftertreatment system of  claim 9 , wherein and the first SCR catalyst is characterized by a NOx conversion efficiency of approximately 90 percent or less. 
     
     
         12 . The aftertreatment system of  claim 9 , wherein the second SCR catalyst is characterized by a NOx conversion efficiency between approximately 50 percent and approximately 80 percent. 
     
     
         13 . The aftertreatment system of  claim 9 , further comprising one of an ammonia oxidation catalyst and a diesel oxidation catalyst downstream of the second SCR catalyst. 
     
     
         14 . The aftertreatment system of  claim 9 , further comprising a substrate having an upstream region and a downstream region, the second SCR catalyst being disposed on the upstream region of the substrate, and one of an ammonia oxidation catalyst and a diesel oxidation catalyst being disposed on the downstream region of the substrate. 
     
     
         15 . The aftertreatment system of  claim 9 , further comprising a mixing tube connected to an inlet of the treatment device, and a reductant injector fluidly connected to the mixing tube upstream of the inlet. 
     
     
         16 . The aftertreatment system of  claim 15 , further comprising a mixer disposed within the mixing tube downstream of the reductant injector and upstream of the inlet. 
     
     
         17 . An exhaust treatment method, comprising:
 generating exhaust with an internal combustion engine, the exhaust comprising between approximately 7 g NOx/kW-hr and approximately 10 g NOx/kW-hr;   directing the exhaust uncatalyzed from the internal combustion engine to a combined particulate filter and SCR catalyst; and   catalytically reducing NOx in the exhaust with the combined particulate filter and SCR catalyst, the combined particulate filter and SCR catalyst forming a first treated exhaust.   
     
     
         18 . The method of  claim 17 , further comprising catalytically reducing the first treated exhaust with an additional SCR catalyst disposed downstream of the combined particulate filter and SCR catalyst, the additional SCR catalyst forming a second treated exhaust. 
     
     
         19 . The method of  claim 18 , further comprising catalytically oxidizing the second treated exhaust with one of an ammonia oxidation catalyst and a diesel oxidation catalyst. 
     
     
         20 . The method of  claim 17 , wherein the uncatalyzed exhaust generated by the engine is characterized by a NO 2  to NO ratio of approximately 1 to 2.