Exhaust system and method for reducing particulate and no2 emissions

Abstract

An exhaust system for reducing particulate and NO 2 emissions from diesel engine exhaust gases. The exhaust system includes a diesel particulate filter, an inlet for receiving the exhaust gases, a first conduit for providing a first fluid connection between the inlet and the diesel particulate filter, and a second conduit for providing a second fluid connection between the inlet and the diesel particulate filter. The exhaust system also includes a diesel oxidation catalyst in the second conduit for catalysing hydrocarbon combustion and the formation of NO 2 and having high I-IC activity and high NO 2 activity, and a fuel injector for injecting fuel upstream of the diesel oxidation catalyst. A valve mechanism for selectively directing exhaust gases from the inlet to the diesel particulate filter through the first conduit or the second conduit is also included. A method for reducing particulate and NO 2 emissions using the exhaust system is also provided.

What is claimed is: 
     
         1 . An exhaust system for reducing particulate and NO 2  emissions from diesel engine exhaust gases, the system comprising:
 a diesel particulate filter;   an inlet for receiving exhaust gases from a diesel engine;   a first conduit capable of providing a first fluid connection between the inlet and the diesel particulate filter;   a second conduit capable of providing a second fluid connection between the inlet and the diesel particulate filter;   a diesel oxidation catalyst in the second conduit, the diesel oxidation catalyst catalysing hydrocarbon combustion and the formation of NO 2  and having high HC activity and high NO 2 activity;   a valve mechanism for selectively directing exhaust gases from the inlet to the diesel particulate filter through the first conduit or the second conduit; wherein exhaust gases that pass from the inlet to the diesel particulate filter through the first conduit but not the second conduit will not encounter a diesel oxidation catalyst; and   a fuel injector for injecting fuel upstream of the diesel oxidation catalyst.   
     
     
         2 . The exhaust system according to  claim 1 , wherein the fuel injector is upstream of the valve mechanism. 
     
     
         3 . The exhaust system according to  claim 1 , wherein the fuel injector is arranged and adapted to direct most or substantially all of the injected fuel directly into the second conduit. 
     
     
         4 . The exhaust system according to  claim 1 , further comprising an exhaust gas aftertreatment unit upstream of the inlet. 
     
     
         5 . The exhaust system according to  claim 4 , wherein the aftertreatment unit is an SCR unit. 
     
     
         6 . The exhaust system according to  claim 1 , wherein the first conduit and the second conduit are substantially concentric. 
     
     
         7 . The exhaust system according to  claim 6 , wherein the second conduit is disposed centrally within the first conduit. 
     
     
         8 . The exhaust system according to  claim 6 , wherein the first conduit is disposed centrally within the second conduit. 
     
     
         9 . A method for reducing particulate and NO 2  emissions from diesel engine exhaust gases using the system of  claim 1 , the method comprising:
 in normal mode, operating the valve mechanism to direct most or all of the exhaust gases entering the inlet, to the diesel particulate filter via the first conduit;   in regeneration mode, operating the valve mechanism to direct most or all of the exhaust gases entering the inlet, to the diesel particulate filter via the second conduit.   
     
     
         10 . The method according to  claim 9 , further comprising, in regeneration mode, injecting fuel via the fuel injector to oxidise on the diesel oxidation catalyst and increase the temperature of exhaust gases reaching the diesel particulate filter to burn at least some particulate matter accumulated therein. 
     
     
         11 . The method according to  claim 10 , further comprising monitoring the temperature of exhaust gases at or downstream of the diesel oxidation catalyst to determine when light-off occurs, and commencing the fuel injection at or after light off. 
     
     
         12 . The method according to  claim 9 , further comprising providing a catalyst to the diesel engine fuel, to catalyse the combustion of particulate matter on the diesel particulate filter. 
     
     
         13 . The method according to  claim 9 , further comprising monitoring a pressure difference over the diesel particulate filter and triggering regeneration mode when a preset pressure difference is reached. 
     
     
         14 . (canceled) 
     
     
         15 . (canceled)