Systems and methods to mitigate nox and hc emissions at low exhaust temperatures

Abstract

Systems and methods are provided for managing low temperature NO x and HC emissions, such as during a cold start of an internal combustion engine. The systems and methods include storing NO x and HC emissions at low temperatures and passively releasing these emissions as the temperature of the exhaust system increases.

What is claimed is: 
     
         1 . A method, comprising:
 storing in an exhaust flowpath, upstream of a NO x  reduction catalyst, hydrocarbon (HC) and oxides of nitrogen (NO x ) emissions from an internal combustion engine during low exhaust temperature operation;   releasing the stored HC and NO x  emissions into the exhaust flowpath as the exhaust temperature increases toward an effective operating temperature; and   treating the released HC and NO x  emissions with an oxidation catalyst and the NO x  reduction catalyst.   
     
     
         2 . The method of  claim 1 , wherein the NO x  reduction catalyst is a selective catalytic reduction catalyst. 
     
     
         3 . The method of  claim 1 , wherein the oxidation catalyst is a hydrocarbon storage device catalyst and storing HC emissions includes storing HC emissions on the surface of the hydrocarbon storage device catalyst. 
     
     
         4 . The method of  claim 3 , further comprising oxidizing the stored HC with the hydrocarbon storage device catalyst. 
     
     
         5 . The method of  claim 1 , wherein storing NO x  emissions includes storing NO x  emissions on the surface of a NO x  storage device catalyst. 
     
     
         6 . The method of  claim 5 , wherein the NO x  storage device is a NO x  adsorber. 
     
     
         7 . The method of  claim 1 , wherein the effective operating temperature is around 200° Celsius. 
     
     
         8 . The method of  claim 1 , further comprising delaying reductant dosing during the low exhaust temperature operation so that a reductant amount dosed into the exhaust flowpath during low exhaust temperature operation is insufficient for the NO x  reduction catalyst to treat the NO x  emissions from the internal combustion engine. 
     
     
         9 . A method, comprising:
 operating an internal combustion engine to produce hydrocarbon (HC) and oxides of Nitrogen (NO x ) emissions into an exhaust flowpath during low exhaust temperature operation;   storing, upstream of a NO x  reduction catalyst, HC and NO x  emissions from the internal combustion engine during low exhaust temperature operation; and   providing a reductant dosing command that treats the NO x  emissions with the NO x  reduction catalyst when the exhaust temperature reaches an effective operating temperature that releases the stored HC and NO x  emissions.   
     
     
         10 . The method of  claim 9 , further comprising delaying reductant dosing during the low exhaust temperature operation so that a reductant amount dosed into the exhaust flowpath during low exhaust temperature operation is insufficient for a NO x  reduction catalyst to treat the NO x  emissions from the internal combustion engine. 
     
     
         11 . The method of  claim 9 , wherein storing HC emissions includes storing HC emissions on the surface of a hydrocarbon storage device catalyst and wherein releasing the stored HC emissions includes oxidizing the HC as the exhaust temperature increases toward the effective operating temperature. 
     
     
         12 . The method of  claim 11 , wherein storing NO x  emissions includes storing NO x  emissions on the surface of a NO x  storage device catalyst. 
     
     
         13 . The method of  claim 12 , wherein the NO x  storage device is a NO x  adsorber. 
     
     
         14 . The method of  claim 9 , wherein the effective operating temperature is around 200° Celsius. 
     
     
         15 . The method of  claim 9 , wherein the NO x  reduction catalyst is a selective catalytic reduction catalyst. 
     
     
         16 . A system, comprising:
 an internal combustion engine;   an exhaust conduit fluidly coupled to the internal combustion engine;   a hydrocarbon storage device fluidly coupled to the exhaust conduit;   a NO x  adsorber fluidly coupled to the exhaust conduit;   a NO x  reduction catalyst downstream of the NO x  adsorber; and   a reductant doser operationally coupled to the exhaust conduit upstream of the NO x  reduction catalyst and downstream of the NO x  adsorber.   
     
     
         17 . The system of  claim 16 , wherein the NO x  reduction catalyst is downstream of the hydrocarbon storage device. 
     
     
         18 . The system of  claim 17 , wherein the reductant doser is operationally coupled to the exhaust conduit downstream of the hydrocarbon storage device and the NO x  adsorber. 
     
     
         19 . The system of  claim 16 , wherein the reductant doser is operationally coupled to the exhaust conduit downstream of the hydrocarbon storage device and the NO x  adsorber. 
     
     
         20 . The system of  claim 16 , further comprising a controller, comprising:
 a NO x  ratio determination module structured to determine an NO x  amount at an outlet of the NO x  reduction catalyst;   a temperature determination module structured to determine a present operating temperature of the exhaust gas in the exhaust flowpath;   a dosing control module structured to determine a reductant doser command in response to the NO x  amount to achieve a desired NO x  emissions from the NO x  reduction catalyst.   
     
     
         21 . The system of  claim 20 , wherein the controller is configured to provide a delayed reductant doser command during low exhaust temperature operating conditions 
     
     
         22 . The system of  claim 16 , wherein the hydrocarbon storage device includes a catalyst configured to store hydrocarbon (HC) emissions thereon during low exhaust temperature operating conditions and to oxidize the stored HC when the exhaust temperature reaches an effective temperature. 
     
     
         23 . The system of  claim 22 , wherein the NO x  adsorber is structured to adsorb NO x  emissions during low exhaust temperature operating conditions and release and oxidize NO x  emissions when the exhaust temperature reached an effective temperature for NO x  conversion over the NO x  reduction device. 
     
     
         24 . The system of  claim 16 , further comprising a first NO x  sensor at an inlet of the hydrocarbon storage device and a second NO x  sensor at an outlet of the NO x  reduction catalyst. 
     
     
         25 . The system of  claim 16 , further comprising a NO x  sensor between the NO x  adsorber and the NO x  reduction catalyst. 
     
     
         26 . The system of  claim 16 , further comprising a NO x  sensor upstream of the NO x  reduction catalyst.