Method and apparatus for regenerating a NOx trap and a particulate trap

Abstract

An apparatus comprises an emission abatement device and a ratio oscillator. The emission abatement device comprises a NOx trap and a particulate trap. The ratio oscillator is configured to oscillate a ratio of the oxygen content and regenerative agent content of a flow advanced to the emission abatement device so as to alternately partially regenerate the NOx trap and the particulate trap for a plurality of cycles. An associated method is disclosed.

1 . A method, comprising the steps of: 
 oscillating a ratio of the oxygen content and regenerative agent content of a flow advanced to an emission abatement device comprising a NOx trap and a particulate trap, and    alternately partially regenerating the NOx trap and the particulate trap for a plurality of cycles in response to the oscillating step.    
   
   
       2 . The method of  claim 1 , wherein: 
 the oscillating step comprises operating a valve so as to oscillate injection of a hydrocarbon fuel into exhaust gas advanced to the emission abatement device, and    the regenerating step comprises (i) partially regenerating the NOx trap with the injected fuel and other regenerative agent present in the exhaust gas each time the ratio is at a higher fuel level, (ii) generating heat each time the ratio is at a higher fuel level, and (iii) partially regenerating the particulate trap with oxygen present in the exhaust gas and with the generated heat each time the ratio is at a lower fuel level.    
   
   
       3 . The method of  claim 1 , wherein the oscillating step comprises oscillating the ratio of the oxygen content and regenerative agent content of exhaust gas advanced to the emission abatement device.  
   
   
       4 . The method of  claim 1 , wherein the oscillating step comprises oscillating injection of regenerative agent into exhaust gas advanced to the emission abatement device.  
   
   
       5 . The method of  claim 4 , wherein the injection oscillating step comprises operating a valve so as to oscillate injection of the regenerative agent into the flow of exhaust gas.  
   
   
       6 . The method of  claim 4 , wherein the injection oscillating step comprises oscillating injection of a fuel into the exhaust gas.  
   
   
       7 . The method of  claim 1 , wherein: 
 the oscillating step comprises oscillating the ratio between higher and lower agent levels, and    the regenerating step comprises (i) partially regenerating the NOx trap when the ratio is at a higher agent level and (ii) partially regenerating the particulate trap when the ratio is at a lower agent level.    
   
   
       8 . The method of  claim 7 , wherein: 
 the regenerating step further comprises generating heat when the ratio is at a higher agent level, and    the step of partially regenerating the particulate trap comprises partially regenerating the particulate trap with the generated heat and oxygen present in the flow.    
   
   
       9 . The method of  claim 1 , wherein the regenerating step comprises (i) commencing partial regeneration of the NOx trap and interrupting partial regeneration of the particulate trap upon commencement of partial regeneration of the NOx trap and (ii) commencing partial regeneration of the particulate trap and interrupting partial regeneration of the NOx trap upon commencement of partial regeneration of the particulate trap.  
   
   
       10 . An apparatus, comprising: 
 a NOx trap and a particulate trap,    an exhaust gas passageway in which the NOx trap and the particulate trap are positioned, and    an agent injection system configured to oscillate injection of a regenerative agent into the exhaust gas passageway between higher and lower agent levels so as to alternately partially regenerate the NOx trap and the particulate trap for a plurality of cycles.    
   
   
       11 . The apparatus of  claim 10 , wherein the agent injection system comprises an agent supply, a flow control device positioned to control flow of the agent from the agent supply to the exhaust gas passageway, and a controller coupled to the flow control device to vary operation thereof to oscillate injection of the regenerative agent.  
   
   
       12 . The apparatus of  claim 10 , wherein the agent injection system comprises a fuel supply to supply fuel as the injected regenerative agent.  
   
   
       13 . The apparatus of  claim 10 , wherein the agent injection system comprises a valve operable to oscillate injection of the regenerative agent.  
   
   
       14 . The apparatus of  claim 13 , wherein the agent injection system comprises a controller coupled to the valve to vary operation of the valve to oscillate injection of the regenerative agent.  
   
   
       15 . An apparatus, comprising: 
 an emission abatement device comprising a NOx trap and a particulate trap, and    a ratio oscillator configured to oscillate a ratio of the oxygen content and regenerative agent content of a flow advanced to the emission abatement device so as to alternately partially regenerate the NOx trap and the particulate trap for a plurality of cycles.    
   
   
       16 . The apparatus of  claim 15 , wherein the ratio oscillator is configured to oscillate the ratio between higher and lower agent levels so as to partially regenerate the NOx trap each time that the ratio is at a higher agent level and to partially regenerate the particulate trap each time that the ratio is at a lower agent level.  
   
   
       17 . The apparatus of  claim 16 , wherein the emission abatement device comprises a catalyst associated with the particulate trap to elevate the temperature of the particulate trap in the presence of oxygen and regenerative agent.  
   
   
       18 . The apparatus of  claim 15 , wherein: 
 the emission abatement device is positioned in an exhaust gas passageway, and    the ratio oscillator comprises a fuel supply to supply a fuel, a valve fluidly coupled to the fuel supply and fluidly coupled to the exhaust gas passageway at a location upstream from the emission abatement device, and a controller coupled to the valve to vary operation thereof to oscillate injection of the fuel into the exhaust gas passageway.    
   
   
       19 . The apparatus of  claim 15 , further comprising an engine fluidly coupled to the emission abatement device, wherein the ratio oscillator is configured to oscillate injection of a regenerative agent into exhaust gas of the engine in response to at least one of a flow of air introduced into the engine, the lambda value of the exhaust gas, and a map of the engine.  
   
   
       20 . The apparatus of  claim 15 , further comprising an engine fluidly coupled to the emission abatement device, wherein the ratio oscillator is coupled to the engine to inject a fuel into the engine.