Exhaust gas aftertreatment systems

Abstract

A method are presented for monitoring an amount of ammonia stored in a urea-based SCR catalyst based on a response of a sensor coupled downstream of the catalyst to a periodic desorbtion of a small amount of ammonia. The sensor could be an ammonia sensor, or a NOx sensor whose signal is sensitive to presence of both NOx and ammonia. The method can be performed at engine start to establish initial ammonia storage amount, or, alternatively, to adjust ammonia storage amounts or diagnose degradation when NOx conversion efficiency of the catalyst is below a predetermined value.

1 . A method for estimating an amount of reductant stored in an exhaust gas aftertreatment device coupled downstream of an internal combustion engine, the device having a sensor coupled downstream of it, the method comprising: 
 adjusting an operating condition to desorb a portion of reductant stored in the device; and    adjusting an amount of reductant injected into the device based on a response of the sensor to said desorbed reductant portion.    
   
   
       2 . The method as set forth in  claim 1  wherein the exhaust gas aftertreatment device is a selective catalytic reduction (SCR) catalyst.  
   
   
       3 . The method as set forth in  claim 2  wherein said reductant is ammonia.  
   
   
       4 . The method as set forth in  claim 3  wherein the engine is a diesel engine.  
   
   
       5 . The method as set forth in  claim 4  wherein said operating condition is a temperature of said SCR catalyst.  
   
   
       6 . The method as set forth in  claim 5  wherein the sensor is a NOx sensor.  
   
   
       7 . The method as set forth in  claim 5  wherein the sensor is an ammonia sensor.  
   
   
       8 . The method as set forth in  claim 1  wherein said operating condition adjustment is done at engine start.  
   
   
       9 . The method as set forth in  claim 1  wherein said operating condition adjustment is done when NOx conversion efficiency of the device is below a predetermined value.  
   
   
       10 . The method as set forth in  claim 9  further comprising providing an indication of degradation if NOx conversion efficiency of the device remains below said predetermined value for a predetermined amount of time following said adjusting of reductant injection into the catalyst.  
   
   
       11 . An aftertreatment system for an internal combustion engine exhaust gas, comprising: 
 an SCR catalyst;    a NOx sensor coupled downstream of said SCR catalyst; and    a controller adjusting an operating condition to desorb a portion of reductant from said SCR catalyst when NOx conversion efficiency of said SCR catalyst is below a predetermined value, said controller monitoring a NOx sensor signal to determine an amount of reductant desorbed, and controlling reductant injection into said SCR catalyst based on said monitored NOx sensor signal.    
   
   
       12 . The system as set forth in  claim 11  wherein said operating condition is a temperature of said SCR catalyst.  
   
   
       13 . The system as set forth in  claim 12  wherein said reductant is ammonia.  
   
   
       14 . The system as set forth in  claim 13  wherein said controller further provides an indication of degradation if NOx conversion efficiency of said SCR catalyst remains below said predetermined value for a predetermined amount of time following said adjusting of reductant injection into the catalyst.  
   
   
       15 . The system as set forth in  claim 14  further comprising regenerating said SCR catalyst in response to said indication of degradation.  
   
   
       16 . A method for controlling reductant injection into an SCR catalyst, comprising: 
 increasing a temperature of the catalyst to a predetermined temperature;    calculating an expected amount of reductant released from the catalyst due to said temperature increase based on a model of the catalyst;    calculating an actual amount of reductant released from the catalyst due to said temperature increase based on a response of a NOx sensor coupled downstream of the SCR catalyst; and    adjusting an amount of reductant injection into the catalyst based on a difference between said actual and said estimated amounts of released reductant.    
   
   
       17 . A method for controlling a NOx-reducing catalyst coupled downstream of an internal combustion engine, the catalyst having a sensor coupled downstream of it, the method comprising: 
 providing an indication of an operating condition;    in response to said indication, desorbing a portion of reductant stored in the catalyst;    adjusting an amount of reductant injection into the catalyst based on a response of the sensor to said desorbtion.    
   
   
       18 . The method as set forth in  claim 17  wherein said NOx-reducing catalyst is an SCR catalyst.  
   
   
       19 . The method as set forth in  claim 18  wherein said sensor is a NOx sensor.  
   
   
       20 . The method as set forth in  claim 19  wherein said sensor is an ammonia sensor.  
   
   
       21 . The method as set forth in  claim 18  wherein said operating condition is engine start.  
   
   
       22 . The method as set forth in  claim 18  wherein said operating condition is a condition wherein NOx conversion efficiency of the catalyst is below a predetermined value.  
   
   
       23 . The method as set forth in  claim 22  wherein said predetermined value is not greater than 95%.  
   
   
       24 . The method as set forth in  claim 22  further comprising regenerating the catalyst if said NOx conversion efficiency remains below said predetermined value for a predetermined amount of time following said adjustment of said amount of injected reductant.