High efficiency conversion of nitrogen oxides in an exhaust aftertreatment device at low temperature

Abstract

A system and method for providing reductant to a lean NOx catalyst, when the temperature in the lean NOx catalyst is greater than 300° C., is disclosed. After the reductant is supplied under these conditions, the NOx conversion efficiency of the lean NOx catalyst in the 140-250° C. temperature range is increased.

1 . A method for controlling reductant added to exhaust gases of an internal combustion engine, the reductant and exhaust gases flowing into a catalyst coupled to the engine, comprising the steps of: 
 providing an indication that temperature of the catalyst is higher than a predetermined temperature;    in response to said indication, adding reductant into the exhaust gases;    providing an estimate of a stored quantity of reductant within the catalyst; and    substantially discontinuing said step of adding reductant when said stored quantity exceeds a predetermined quantity.    
     
     
         2 . The method of  claim 1  wherein said predetermined quantity is based on a reductant storage capacity of the catalyst.  
     
     
         3 . The method of  claim 1  wherein said predetermined temperature is 300 degrees Celsius.  
     
     
         4 . The method of  claim 2  wherein said reductant storage capacity of the catalyst depends on a temperature of the catalyst.  
     
     
         5 . The method of  claim 1  wherein the reductant is added by an injector disposed upstream of the catalyst and downstream of the engine.  
     
     
         6 . The method of  claim 1  wherein the reductant contains ammonia.  
     
     
         7 . The method of  claim 1  wherein the reductant is added by an injector disposed in a combustion chamber of the engine.  
     
     
         8 . A system for controlling reductant addition into lean exhaust gases discharged from an internal combustion engine, the reductant being added upstream of a catalyst coupled to the engine, comprising: 
 an injector for adding the reductant into the exhaust gases; and    an engine controller operably connected to the engine and said injector which actuates said injector to supply the reductant in response to an indication that temperature of the catalyst is greater than a predetermined temperature, provides an estimate of a quantity of reductant stored in the catalyst, and when said quantity exceeds a predetermined quantity, substantially discontinues said addition of reductant.    
     
     
         9 . The system of  claim 8 , further comprising a temperature sensor disposed upstream of the catalyst providing said indication of temperature.  
     
     
         10 . The system of  claim 8 , further comprising an exhaust gas component sensor disposed in an exhaust line downstream of the catalyst and coupled to said engine control unit.  
     
     
         11 . The system of  claim 10 , wherein said exhaust gas component sensor is a reductant sensor and said engine control unit discontinues said addition of reductant based on a signal from said reductant sensor.  
     
     
         12 . The system of  claim 10 , wherein said exhaust gas component sensor is a NOx sensor.  
     
     
         13 . The system of  claim 12 , wherein a signal from said NOx sensor is used in said estimation of a quantity of reductant stored in the catalyst.  
     
     
         14 . The system of  claim 8 , wherein said reductant contains ammonia.  
     
     
         15 - 16 . (canceled)  
     
     
         17 . A computer readable storage medium having stored data representing instructions executable by a computer to control an injector which supplies reductant into exhaust gases discharged from an internal combustion engine, wherein the exhaust gases contain excess oxygen, the reductant being added to the exhaust gases upstream of a catalyst coupled to the engine, comprising: 
 instructions for providing an indication of a temperature of the catalyst; and    instructions for commanding the injector to supply reductant when said indicated temperature is greater than a threshold temperature; and    instructions to substantially reduce said injection of reductant when a quantity of reductant stored in the catalyst is substantially equal to a predetermined quantity .    
     
     
         18 . The storage medium of  claim 17  wherein a reductant sensor is disposed in an exhaust duct downstream of the catalyst, further comprising instructions to substantially discontinue said injection of reductant based on a signal from said reductant sensor.  
     
     
         19 . A method for controlling reductant added to exhaust gases of an internal combustion engine, the reductant and exhaust gases flowing into a catalyst coupled to the engine, comprising the steps of: 
 determining a temperature in the catalyst; 
 estimating a stored quantity of reductant in the catalyst;  
 adding reductant to the exhaust gases when said catalyst temperature is greater than a predetermined temperature and said stored quantity is less than a first predetermined quantity; and  
 discontinuing said step of adding reductant when said stored quantity is greater than a second predetermined quantity, said second predetermined quantity being greater than or equal to said first predetermined quantity.  
   
     
     
         20 . A system for controlling an amount of reductant added to exhaust gases from an internal combustion engine, comprising the steps of: 
 an injector for adding the reductant into the engine exhaust gases upstream of a catalyst coupled to said engine; and    an engine controller operably connected to said engine and said injector, said controller configured to actuate said injector to supply said reductant at a rate greater than a consumption rate of reductant in said catalyst when a temperature of said catalyst is greater than a predetermined temperature, said controller further configured to estimate a quantity of reductant stored in said catalyst, said controller further configured to substantially discontinue said addition of reductant when said quantity of stored reductant exceeds a predetermined quantity.    
     
     
         21 . The system of  claim 20  wherein said supplying rate of said reductant is substantially greater than a consumption rate of said reductant in said catalyst.  
     
     
         22 . A method for controlling reductant added to exhaust gases from an internal combustion engine, the reductant and exhaust gases flowing into a catalyst coupled to the engine, comprising the steps of: 
 adding reductant into the exhaust gases at a first delivery rate;    indicating when a temperature of the catalyst is greater than a predetermined temperature; 
 adding reductant at a second delivery rate into the exhaust gases in response to said indication,  
 estimating of a stored quantity of reductant within the catalyst; and  
   adding reductant at said first delivery rate when said stored quantity exceeds a predetermined quantity, said first delivery rate being less than said second delivery rate.    
     
     
         23 . The method of  claim 22  wherein said first delivery rate equals zero.  
     
     
         24 . The method of  claim 22  wherein said first delivery rate is substantially less than said second delivery rate.  
     
     
         25 . A method for reducing NOx in exhaust gases from an engine, said engine communicating exhaust gases to a catalyst, comprising the steps of: 
 storing reductant on active sites of said catalyst when a temperature of the catalyst is greater than a predetermined temperature; and,    utilizing only said stored reductant in said catalyst for reducing NOx in said exhaust gases for a first time period.    
     
     
         26 . The method of  claim 25  further comprising: 
 supplying additional reductant to said catalyst after said first time period to reduce NOx in said exhaust gases and to store additional reductant on said active sites.    
     
     
         27 . A method for reducing NOx in exhaust gases from an engine, said engine communicating exhaust gases to a lean NOx catalyst, comprising the steps of: 
 iteratively supplying pulses of reductant to a lean NOx catalyst during engine operation, wherein between said pulses of reductant a portion of reductant stored in said lean NOx catalyst is utilized to continue reducing NOx, said pulsing commences when temperature in said lean NOx catalyst exceeds a predetermined temperature, and said pulsing terminates when an estimate of a quantity of reductant stored in the catalyst exceeds a predetermined quantity.