Fuel-fired burner for no2 based regeneration

Abstract

A fuel-fired burner in a vehicle exhaust system is selectively activated to increase exhaust gas temperature to a desired reference temperature. The fuel-fired burner can be either a partial range burner or a full range burner. A control strategy activates the fuel-fired burner only when needed to provide NO 2 based passive regeneration of a diesel particulate filter in a fuel efficient manner. The control strategy includes at least one of a look-up table which outputs the desired reference temperature as a function of engine operating conditions, a comparison of pressure characteristics to predetermined thresholds, and a steady-state model or a transient model that outputs the desired reference temperature as a function of exhaust back-pressure and estimated exhaust oxygen flowrate.

1 . A method of operating a fuel-fired burner in a vehicle exhaust system comprising the steps of:
 (a) associating a fuel-fired burner with a diesel particulate filter assembly;   (b) monitoring at least one engine operating condition;   (c) monitoring exhaust gas temperature;   (d) communicating engine operating condition information and the exhaust gas temperature to a controller including a control strategy to identify when the fuel-fired burner should be activated to achieve a desired reference temperature to increase NO 2  levels sufficiently to regenerate the diesel particulate filter; and   (e) generating a control signal to activate the fuel-fired burner to raise exhaust gas temperature to the desired reference temperature only when the control strategy identifies that the fuel-fired burner should be activated.   
     
     
         2 . The method according to  claim 1  wherein the fuel-fired burner comprises a partial range fuel-fired burner. 
     
     
         3 . The method according to  claim 2  including monitoring at least two engine operating conditions, and wherein the control strategy comprises a look-up table which outputs the desired reference temperature as a function of the engine operating conditions, and including generating the control signal to inject fuel into the partial range fuel-fired burner until the desired reference temperature is achieved. 
     
     
         4 . The method according to  claim 2  wherein the control strategy comprises a steady-state model that outputs the desired reference temperature as a function of exhaust back-pressure and estimated exhaust oxygen flowrate. 
     
     
         5 . The method according to  claim 5  including generating the control signal to operate the partial range fuel-fired burner at temperatures of 250 degrees Celsius or greater as a function of estimated oxygen by mass flowrate and measured back-pressure. 
     
     
         6 . The method according to  claim 2  wherein the control strategy comprises a transient model that outputs the desired reference temperature as a function of exhaust back-pressure and estimated exhaust oxygen flowrate. 
     
     
         7 . The method according to  claim 6  including generating the control signal to operate the partial range fuel-fired burner at temperatures of 250 degrees Celsius or greater as a function of estimated oxygen by mass flowrate and measured back-pressure. 
     
     
         8 . The method according to  claim 6  wherein the transient model comprises a pre-filter and a steady-state model that outputs the desired reference temperature as a function of model inputs including exhaust back-pressure and estimated exhaust oxygen flowrate, and wherein the pre-filter attenuates noise and disturbances from model input signals. 
     
     
         9 . The method according to  claim 1  including continuously monitoring a pressure drop across the diesel particulate filter, comparing the pressure drop to a look-up table of pressure drop versus the engine operating condition, and only activating the fuel-fired burner if the pressure drop exceeds a predetermined threshold, exhaust gas temperature is below 300 degrees Celsius, and a rate of pressure of pressure increase exceeds a predetermined rate threshold. 
     
     
         10 . The method according to  claim 9  including deactivating the fuel-fired burner when the pressure drop falls below the predetermined threshold and/or exhaust temperature increases above 300 degrees Celsius. 
     
     
         11 . A vehicle exhaust system comprising:
 a fuel-fired burner;   a diesel particulate filter assembly; and   a controller electrically coupled to the fuel-fired burner, the controller including a processor and a memory device electrically coupled to the processor, the memory device storing a plurality of instructions that include a control strategy to identify when the fuel-fired burner should be activated to achieve a desired reference temperature to increase NO 2  levels sufficiently to regenerate the diesel particulate filter, and wherein when the processor executes the plurality of instructions, the processor is caused to:   receive engine operating condition information and exhaust gas temperature information, and   generate a control signal to activate the fuel-fired burner to raise exhaust gas temperature to the desired reference temperature only when the control strategy identifies conditions are proper for activating the fuel-fired burner.   
     
     
         12 . The vehicle exhaust system according to  claim 11  wherein the control strategy comprises a look-up table which outputs the desired reference temperature as a function of the engine operating conditions, and wherein fuel is injected into the fuel-fired burner in response to the control signal until the desired reference temperature is achieved. 
     
     
         13 . The vehicle exhaust system according to  claim 12  wherein the control strategy comprises a steady-state model that outputs the desired reference temperature as a function of exhaust back-pressure and estimated exhaust oxygen flowrate. 
     
     
         14 . The vehicle exhaust system according to  claim 11  wherein the control strategy comprises a transient model that outputs the desired reference temperature as a function of exhaust back-pressure and estimated exhaust oxygen flowrate. 
     
     
         15 . The vehicle exhaust system according to  claim 14  wherein the transient model comprises a pre-filter and a steady-state model that outputs the desired reference temperature as a function of model inputs including exhaust back-pressure and estimated exhaust oxygen flowrate, and wherein the pre-filter attenuates noise and disturbances from model input signals. 
     
     
         16 . The vehicle exhaust system according to  claim 11  wherein the controller continuously monitoring a pressure drop across the diesel particulate filter, compares the pressure drop to a look-up table of pressure drop versus the engine operating condition, and only activates the fuel-fired burner if the pressure drop exceeds a predetermined threshold, exhaust gas temperature is below 300 degrees Celsius, and a rate of pressure increase exceeds a predetermined rate threshold. 
     
     
         17 . The vehicle exhaust system according to  claim 11  wherein the diesel particulate filter comprises a catalyzed diesel particulate filter. 
     
     
         18 . The vehicle exhaust system according to  claim 11  wherein the fuel-fired burner comprises one of a partial range fuel-fired burner or a full range fuel-fired burner. 
     
     
         19 . A method of operating a fuel-fired burner in a vehicle exhaust system comprising the steps of:
 (a) continuously monitoring a pressure drop across a diesel particulate filter;   (b) continuously monitoring exhaust temperature;   (c) comparing the pressure drop to a look-up table of pressure drop versus an engine operating condition and comparing the exhaust temperature to a threshold temperature; and   (d) selectively activating a fuel-fired burner to increase NO 2  levels sufficiently to regenerate the diesel particulate filter only when predetermined pressure and temperature criteria are met.   
     
     
         20 . The method according to claim  21  wherein the fuel-fired burner comprises a partial range fuel-fired burner and wherein step (d) further includes activating the partial range fuel-fired burner if the pressure drop exceeds a predetermined threshold, exhaust gas temperature is below 300 degrees Celsius, and a rate of pressure increase exceeds a predetermined rate threshold.