Method for regenerating a diesel particulate filter

Abstract

A method is disclosed for regenerating a diesel particulate filter without excessively increasing NO 2 emissions. The system includes a fuel delivery device, an oxidation catalyst, and a diesel particulate filter. During a first operational mode, the fuel injection device injects a relatively smaller amount of fuel into the exhaust stream to reduce the capacity of the oxidation catalyst to oxidize NO in the exhaust stream to NO 2 . At a determined time, a second operational mode is initiated where a relatively larger amount of fuel is injected into the exhaust stream and is oxidized within the oxidation catalyst, thereby raising the exhaust temperature sufficiently to combust substantially all of the soot trapped on the diesel particulate filter.

1 . A method for injecting fuel into an exhaust system of a diesel engine that includes an oxidation catalyst and a diesel particulate filter for regenerating the diesel particulate filter, the method comprising: 
 injecting fuel at a first fuel injection rate a majority of the engine operational time to reduce the formation of NO 2  in the oxidation catalyst; and    injecting fuel at a second fuel injection rate a minority of the engine operational time to fully regenerate the diesel particulate filter.    
   
   
       2 . The method of  claim 1  wherein the injection of fuel at the first fuel injection rate comprises 50 to 95 percent of the engine operational time and the injection of fuel at the second fuel injection rate comprises 0.001 to 5 percent of the engine operational time.  
   
   
       3 . The method of  claim 1  wherein the first fuel injection rate is selected so that the ratio of NO 2  to NO x  in the exhaust gas emitted to the atmosphere is no more than 20 percent greater than the ratio of NO 2  to NO x  emitted from the engine.  
   
   
       4 . A method for injecting fuel into an exhaust system of a diesel engine that includes an oxidation catalyst and a diesel particulate filter for regenerating the diesel particulate filter, the method comprising: 
 determining whether the diesel particulate filter requires regeneration;    injecting fuel at a first fuel injection rate when the diesel particulate filter does not require regeneration, said first fuel injection rate being insufficient to regenerate the diesel particulate filter; and    injecting fuel at a second fuel injection rate when the diesel particulate filter requires regeneration, said second fuel injection rate being sufficient to regenerate the diesel particulate filter.    
   
   
       5 . The method of  claim 4  wherein the first fuel injection rate is determined from a pressure measured in an air intake manifold, an oxygen content measured in the exhaust stream, a temperature measured in the exhaust stream at the turbocharger outlet, and the engine power output.  
   
   
       6 . A method for reducing NO 2  emissions in an exhaust system for conveying an exhaust stream from an engine, the system including a substrate positioned within the exhaust stream, the method comprising: 
 injecting fuel into the exhaust stream at a location between the engine and the substrate, the injection of fuel taking place for a majority of an operating time of the engine.    
   
   
       7 . The method of  claim 6 , wherein the substrate is catalyzed.  
   
   
       8 . The method of  claim 6 , wherein the substrate includes corrugated metal.  
   
   
       9 . The method of  claim 6 , wherein the substrate includes ceramic.  
   
   
       10 . The method of  claim 7 , wherein the substrate includes corrugated metal.  
   
   
       11 . The method of  claim 7 , wherein the substrate includes ceramic.  
   
   
       12 . The method of  claim 7 , wherein the substrate comprises an oxidation catalyst.  
   
   
       13 . The method of  claim 6 , wherein the fuel is injected at a rate dependent upon a mass flow rate of NO 2  in the exhaust stream.  
   
   
       14 . The method of  claim 13 , wherein the mass flow rate of NO 2  is a predicted mass flow rate.  
   
   
       15 . The method of  claim 6 , wherein the fuel is injected whenever a temperature of the exhaust stream is sufficient to support the catalyzed production of NO 2 .  
   
   
       16 . The method of  claim 15 , wherein the temperature is greater than 180 degrees C.  
   
   
       17 . The method of  claim 6 , wherein the injection of fuel does not cause the substrate to regenerate.  
   
   
       18 . The method of  claim 6 , wherein the injection of fuel does not cause the substrate to exceed a temperature of 500 degrees C.  
   
   
       19 . The method of  claim 6 , wherein the fuel is injected at a rate selected so that the ratio of NO 2  to NO x  in the exhaust gas emitted to the atmosphere is no more than 20 percent greater than the ratio of NO 2  to NO x  emitted from the engine.  
   
   
       20 . The method of  claim 6 , wherein an operating time of the engine is 24 hours, and wherein the injection of fuel takes place for at least 12 of the 24 hours.