Exhaust gas aftertreatment systems

Abstract

A method is presented for determining an amount of reductant stored in the catalyst by intrusively desorbing a portion of reductant and monitoring the response of an reductant sensor to the desorbed portion. The desorbtion can be performed at vehicle start-up to determine initial storage amount and to adjust reductant injection accordingly to achieve optimum storage. Additionally, a portion of reductant can be desorbed when NOx conversion efficiency of the catalyst is reduced in order to diagnose the component responsible for system degradation.

1 . A diagnostic system, comprising: 
 an engine;    a catalyst coupled downstream of said engine, comprising: 
 a first catalyst brick, said brick having a heated portion; and  
 a sensor coupled in close proximity to said heated portion; and  
 a controller adjusting a temperature of said heated portion of said first catalyst brick to desorb reductant stored on said heated portion, said controller adjusting an amount of reductant in an exhaust gas mixture entering said catalyst based on a response of said sensor to said desorbed reductant; and providing an indication of catalyst degradation if an amount of an exhaust gas component downstream of said catalyst remains above a predetermined value for a predetermined time following said controller adjusting said amount of reductant entering said catalyst.  
   
   
   
       2 . The system as set forth in  claim 1  wherein said engine is a diesel engine.  
   
   
       3 . The system as set forth in  claim 2  wherein said catalyst is a NOx-reducing catalyst.  
   
   
       4 . The system as set forth in  claim 3  wherein said NOx-reducing catalyst is a urea SCR catalyst.  
   
   
       5 . The system as set forth in  claim 4  wherein said heated portion of said first catalyst brick is an electrically heated portion adjusted to a predetermined temperature based on the catalyst desorption characteristics.  
   
   
       6 . The system as set forth in  claim 5  wherein said sensor is an ammonia sensor.  
   
   
       7 . The system as set forth in  claim 6  wherein said reductant is ammonia.  
   
   
       8 . The system as set forth in  claim 7  wherein said controller adjusts said temperature of said heated portion of said first catalyst brick to desorb substantially all reductant stored on said heated portion.  
   
   
       9 . The system as set forth in  claim 9  wherein controller adjusts an amount of reductant in an exhaust gas mixture entering said catalyst to cause a predetermined amount of ammonia to be stored in said first catalyst brick.  
   
   
       10 . The system as set forth in  claim 9  wherein said catalyst further comprises a second catalyst brick.  
   
   
       11 . The system as set forth in  claim 10  wherein said controller provides said indication of catalyst degradation if an amount of Nox downstream of said catalyst remains above a predetermined value for a predetermined amount of time.  
   
   
       12 . The system as set forth in  claim 11  further comprising regenerating said catalyst in response to said controller generating said indication of degradation.  
   
   
       13 . A method for controlling a NOx-reducing catalyst coupled downstream of an internal combustion engine, the NOx-reducing catalyst including an embedded heater and an ammonia sensor coupled in close proximity to the embedded heater, the method comprising: 
 providing an indication of catalyst degradation;    in response to said indication, adjusting the heater temperature thereby causing reductant to desorb from the catalyst;    adjusting an amount of reductant injection into the catalyst based on an amount of reductant desorbed by said heating, said desorbed amount determined by monitoring the ammonia sensor signal; and    regenerating the catalyst if an amount of NOx downstream of the catalyst remains above a predetermined value for a predetermined time following said adjusting of reductant injection into the catalyst.    
   
   
       14 . The method as set forth in  claim 13  wherein said catalyst degradation is NOx conversion efficiency degradation.  
   
   
       15 . The method as set forth in  claim 14  further comprising determining an amount of reductant stored in the catalyst based on said sensor response to said reductant desorbtion.  
   
   
       16 . A method for diagnosing a NOx-reducing catalyst having a heater embedded therein, the catalyst further having a reductant sensor positioned in close proximity to the embedded heater, the method comprising: 
 adjusting a temperature of the embedded heater to desorb a portion of reductant stored in the NOx-reducing catalyst;    subsequently adjusting reductant injection into the catalyst based on a response of the sensor to said desorbtion; and    regenerating the catalyst    
   
   
       17 . A method for controlling a NOx-reducing catalyst, comprising: 
 intrusively desorbing a portion of reductant stored in the catalyst;    adjusting reductant injection into the catalyst based on an amount of reductant intrusively desorbed; and    regenerating the catalyst when NOx conversion efficiency of the catalyst remains below a predetermined value for a predetermined amount of time following said reductant injection adjustment.