Exhaust system utilizing a low-temperature oxidation catalyst

Abstract

An exhaust treatment system is provided having a first exhaust passageway fluidly connected to an engine. A particulate filter and a selective catalytic reduction catalyst are situated within the first exhaust passageway. In addition, the system has a first oxidation catalyst located within the first exhaust passageway upstream of the particulate filter and the selective catalytic reduction catalyst. The system also has a second exhaust passageway fluidly connected to the first exhaust passageway upstream and downstream of the first oxidation catalyst. The exhaust treatment system further has a sensor configured to sense a parameter indicative of an exhaust gas temperature. Furthermore, the system has a controller configured to direct exhaust gas through the first oxidation catalyst when the exhaust gas temperature is below a threshold temperature and direct the exhaust gas through the second exhaust passageway when the exhaust gas temperature is above the threshold temperature.

1 . An exhaust treatment system, comprising:
 a first exhaust passageway fluidly connected to an engine;   a particulate filter located within the first exhaust passageway;   a selective catalytic reduction catalyst situated within the first exhaust passageway;   a first oxidation catalyst located within the first exhaust passageway upstream of the particulate filter and the selective catalytic reduction catalyst;   a second exhaust passageway fluidly connected to the first exhaust passageway upstream and downstream of the first oxidation catalyst;   a sensor configured to sense a parameter indicative of an exhaust gas temperature; and   a controller configured to direct exhaust gas through the first oxidation catalyst when the exhaust gas temperature is below a threshold temperature, and direct the exhaust gas through the second exhaust passageway when the exhaust gas temperature is above the threshold temperature.   
   
   
       2 . The exhaust treatment system of  claim 1 , wherein the threshold temperature is approximately 250 degrees Celsius. 
   
   
       3 . The exhaust treatment system of  claim 2 , wherein the first oxidation catalyst has a light-off temperature below approximately 200 degrees Celsius. 
   
   
       4 . The exhaust treatment system of  claim 3 , further including a second oxidation catalyst located within the second exhaust gas passageway and having a light-off temperature above approximately 200 degrees Celsius. 
   
   
       5 . The exhaust treatment system of  claim 4 , wherein the controller is configured to direct exhaust gas in parallel through both the first and second exhaust passageways when the exhaust gas temperature is within a predetermined temperature range. 
   
   
       6 . The exhaust treatment system of  claim 5 , wherein the predetermined temperature range is between approximately 200 degrees Celsius and approximately 250 degrees Celsius. 
   
   
       7 . The exhaust treatment system of  claim 1 , wherein the first oxidation catalyst has a light-off temperature of approximately 150 degrees Celsius. 
   
   
       8 . The exhaust treatment system of  claim 1 , wherein the first oxidation catalyst has a platinum based catalyst supported on a platform including cerium. 
   
   
       9 . The exhaust treatment system of  claim 1 , wherein the first oxidation catalyst has a gold based catalyst supported on a titanium or iron platform. 
   
   
       10 . A method for generating NO 2 , comprising:
 sensing a temperature of an exhaust gas; and   oxidizing the exhaust gas at a first location only when the exhaust gas temperature is below a threshold temperature.   
   
   
       11 . The method of  claim 10 , wherein the threshold temperature is approximately 250 degrees Celsius. 
   
   
       12 . The method of  claim 10 , further including oxidizing the exhaust gas at a second location only when the exhaust gas temperature is above the threshold temperature. 
   
   
       13 . The method of  claim 12 , wherein the threshold temperature is approximately 200 degrees Celsius. 
   
   
       14 . A power system, comprising:
 an engine configured to combust a fuel/air mixture and produce a flow of exhaust;   a first exhaust passageway fluidly connected to receive the flow of exhaust from the engine;   a particulate filter situated within the first exhaust passageway;   a selective catalytic reduction catalyst situated within the first exhaust passageway;   a first oxidation catalyst located within the first exhaust passageway upstream of the particulate filter and the selective catalytic reduction catalyst;   a second exhaust passageway fluidly connected to the first exhaust passageway upstream and downstream of the first oxidation catalyst;   a sensor configured to sense a parameter indicative of an exhaust gas temperature; and   a controller configured to direct exhaust gas through the first oxidation catalyst when the exhaust gas temperature is below a threshold temperature, and direct the exhaust gas through the second exhaust passageway when the exhaust gas temperature is above the threshold temperature.   
   
   
       15 . The power system of  claim 14 , wherein the threshold temperature is approximately 250 degrees Celsius. 
   
   
       16 . The power system of  claim 15 , wherein the first oxidation catalyst has a light-off temperature below approximately 200 degrees Celsius. 
   
   
       17 . The power system of  claim 16 , further including a second oxidation catalyst located within the second exhaust gas passageway and having a light-off temperature above approximately 200 degrees Celsius. 
   
   
       18 . The power system of  claim 17 , wherein the controller is configured to direct exhaust gas through both the first and second exhaust passageways in parallel when the exhaust gas temperature is within a predetermined temperature range. 
   
   
       19 . The power system of  claim 18 , wherein the predetermined temperature range is between approximately 200 degrees Celsius and approximately 250 degrees Celsius. 
   
   
       20 . The power system of  claim 14 , wherein the first oxidation catalyst has a light-off temperature of approximately 150 degrees Celsius.