Exhaust system for a vehicle

Abstract

An exhaust system for a vehicle includes a passageway, a selective catalytic reduction system, a diesel particulate filter, a urea injection system, and a hydrolysis catalyst. The passageway is operable to direct a flow of exhaust gas emitted from an engine of the vehicle. The selective catalytic reduction system and the diesel particulate filter are positioned along the passageway spaced from one another. The urea injection system includes an injection port positioned along the passageway upstream of the selective catalytic reduction system. The urea injection system is operable to inject urea into the passageway. The hydrolysis catalyst coats at least a portion of the diesel particulate filter. Urea injected into the passageway through the injection port decomposes into ammonia and carbon dioxide upon contact with the hydrolysis catalyst. Thus, the decomposition of the urea is not dependent on mixing the urea with the exhaust gases.

What is claimed is: 
     
         1 . An exhaust system for a vehicle comprising:
 a passageway operable to direct a flow of exhaust gas emitted from an engine of the vehicle;   a selective catalytic reduction system positioned along the passageway;   a diesel particulate filter positioned along the passageway spaced from the selective catalytic reduction system;   a urea injection system including an injection port positioned along the passageway upstream of the selective catalytic reduction system, the urea injection system operable to inject urea into the passageway; and   a hydrolysis catalyst coating on at least a portion of the diesel particulate filter, wherein urea injected into the passageway through the injection port decomposes into ammonia and carbon dioxide upon contact with the hydrolysis catalyst.   
     
     
         2 . The exhaust system of  claim 1 , wherein the hydrolysis catalyst coating coats less than a full length of the diesel particulate filter along the passageway. 
     
     
         3 . The exhaust system of  claim 2 , wherein the hydrolysis catalyst coating coats a leading edge of the diesel particulate filter along the passageway. 
     
     
         4 . The exhaust system of  claim 3 , wherein the urea injection system is positioned upstream of and adjacent to the leading edge of the diesel particulate filter. 
     
     
         5 . The exhaust system of  claim 4 , wherein the exhaust system further comprises a diesel oxidation catalyst positioned along the passageway upstream of and spaced from the diesel particulate filter, and wherein the urea injection system is positioned between the diesel oxidation catalyst and the diesel particulate filter. 
     
     
         6 . The exhaust system of  claim 2 , wherein the hydrolysis catalyst coating coats less than one quarter of the full length of the diesel particulate filter along the passageway. 
     
     
         7 . The exhaust system of  claim 1 , wherein the injection port directs urea into the passageway in a direction transverse to a direction of exhaust flow. 
     
     
         8 . The exhaust system of  claim 7 , wherein the direction of the injection port is perpendicular to the direction of the exhaust flow. 
     
     
         9 . The exhaust system of  claim 2 , wherein the hydrolysis catalyst coating coats a trailing edge of the diesel particulate filter along the passageway. 
     
     
         10 . The exhaust system of  claim 9 , wherein the urea injection system is positioned downstream of and adjacent to the trailing edge of the diesel particulate filter. 
     
     
         11 . The exhaust system of  claim 10 , wherein a direction of the injection port is at least partially opposite to a direction of exhaust flow.