Exhaust system having doc regeneration strategy

Abstract

An exhaust system for use with a combustion engine is disclosed. The exhaust system may have an exhaust passage configured to receive a flow of exhaust from the combustion engine, and an oxidation catalyst disposed within the exhaust passage. The exhaust system may also have a fuel injector configured to selectively inject fuel into the exhaust at a location upstream of the oxidation catalyst, a temperature sensor configured to generate a signal indicative of a temperature of exhaust flowing through the exhaust passage, and a controller in communication with the fuel injector and the temperature sensor. The controller may be configured to make a determination based on the signal that an oxide layer has formed on the oxidation catalyst, and to regulate operation of the fuel injector to inject fuel and reduce the oxide layer based on the determination.

1 . An exhaust system for a combustion engine, comprising:
 an exhaust passage configured to receive a flow of exhaust from the combustion engine;   an oxidation catalyst disposed within the exhaust passage;   a fuel injector configured to selectively inject fuel into the exhaust at a location upstream of the oxidation catalyst;   a temperature sensor configured to generate a signal indicative of a temperature of exhaust flowing through the exhaust passage; and   a controller in communication with the fuel injector and the temperature sensor, the controller being configured to:
 make a determination based on the signal that an oxide layer has formed on the oxidation catalyst; and 
 regulate operation of the fuel injector to inject fuel and reduce the oxide layer based on the determination. 
   
     
     
         2 . The exhaust system of  claim 1 , wherein the controller is configured to make the determination that an oxide layer has formed when the signal indicates a temperature of exhaust flowing through the exhaust passage has exceeded a threshold temperature. 
     
     
         3 . The exhaust system of  claim 2 , wherein the controller is configured to make the determination that an oxide layer has formed when the signal indicates the temperature of exhaust flowing through the exhaust passage has remained above the threshold temperature for a threshold period of time. 
     
     
         4 . The exhaust system of  claim 2 , wherein the threshold temperature is a temperature at which about 60-100% of the oxidation catalyst is covered by the oxide layer. 
     
     
         5 . The exhaust system of  claim 4 , wherein the fuel injected by the fuel injector to reduce the oxide layer changes an air-to-fuel ratio of the flow of exhaust by less than about 5%. 
     
     
         6 . The exhaust system of  claim 4 , wherein the fuel injected by the fuel injector to reduce the oxide layer raises temperatures by less than about 30° C. 
     
     
         7 . The exhaust system of  claim 4 , wherein the fuel injected by the fuel injector during a single burst to reduce the oxide layer is about 100 to 1000 ppm in the flow of exhaust, and the controller is configured to continue the injections at about five minute intervals as long as the temperature of exhaust flowing through the exhaust passage remains above the threshold temperature. 
     
     
         8 . The exhaust system of  claim 2 , wherein the controller is configured to regulate operation of the fuel injector to inject fuel when the signal indicates the exhaust flowing through the exhaust passage is cooling. 
     
     
         9 . The exhaust system of  claim 1 , further including an exhaust treatment device disposed within the exhaust passage downstream of the oxidation catalyst. 
     
     
         10 . The exhaust system of  claim 9 , wherein the exhaust treatment device is one of a particulate filter configured to regenerate in the presence of NO 2  generated by the oxidation catalyst or a reduction device configured to reduce a constituent of the exhaust in the presence of NO and NO 2  generated by the oxidation catalyst. 
     
     
         11 . A method of operating an exhaust system, comprising:
 directing exhaust through an oxidation catalyst;   making a determination that an oxide layer has formed on the oxidation catalyst; and   selectively introducing a burst of fuel into exhaust directed through the oxidation catalyst to reduce the oxide layer based on the determination.   
     
     
         12 . The method of  claim 11 , wherein making the determination includes determining that a temperature of the exhaust has exceeded a threshold temperature. 
     
     
         13 . The method of  claim 12 , wherein making the determination further includes determining that the temperature of the exhaust has remained above the threshold temperature for a threshold period of time. 
     
     
         14 . The method of  claim 12 , wherein the threshold temperature is a temperature at which about 60-100% of the oxidation catalyst is covered with the oxide layer. 
     
     
         15 . The method of  claim 14 , wherein selectively introducing bursts of fuel increases an air-to-fuel ratio of the exhaust by less than about 5%. 
     
     
         16 . The method of  claim 14 , wherein selectively introducing bursts of fuel increases a temperature of the exhaust by less than about 30° C. 
     
     
         17 . The method of  claim 14 , wherein the fuel injected during a single burst of fuel is about 100 to 1000 ppm in the exhaust, and the method further includes continuing to introduce bursts of fuel at about five minute intervals as long as the temperature of the exhaust remains above the threshold temperature. 
     
     
         18 . The method of  claim 11 , wherein selectively introducing bursts of fuel includes selectively introducing bursts of fuel when the exhaust is cooling. 
     
     
         19 . The method of  claim 11 , further including directing exhaust from the oxidation catalyst through at least one of a particulate filter and a reduction catalyst. 
     
     
         20 . A power system, comprising:
 an internal combustion engine configured to combust fuel and generate a flow of exhaust;   an exhaust passage leading from the internal combustion engine to the atmosphere;   an oxidation catalyst disposed within the exhaust passage to convert NO to NO 2 ;   a particulate filter disposed downstream of the oxidation catalyst configured to passively regenerate in the presence of the NO 2 ;   a fuel injector configured to selectively inject fuel into the exhaust passage at a location upstream of the oxidation catalyst;   a temperature sensor configured to generate a signal indicative of a temperature of exhaust flowing through the exhaust passage; and   a controller in communication with the fuel injector and the temperature sensor, the controller being configured to:
 make a determination based on the signal that temperature indicative of formation of an oxide layer on the oxidation catalyst has been exceeded; and 
 regulate operation of the fuel injector to inject fuel and reduce the oxide layer based on the determination, 
   wherein the fuel injected by the fuel injector changes an air-to-fuel ratio of the exhaust by less than 5% and raises a temperature of the exhaust by less than 30° C.