Diesel aftertreatment systems

Abstract

An accurate thermodynamic model of an Active Lean NOx (ALNC) Catalyst is presented. The model takes into account hydrocarbon storage and release mechanisms of the ALNC, as well as the degradation in the ALNC hydrocarbon conversion efficiency due to ageing, and thus provides a more accurate estimate of an exotherm generated by hydrocarbon combustion in the ALNC. The estimated exotherm can them be used to detect system degradation and identify components responsible for the degradation.

1 . A method for diagnosing degradation of a NOx-reducing catalyst, comprising: 
 calculating an actual exotherm across the catalyst based on temperature measurements upstream and downstream of the catalyst;    calculating an expected exotherm across the catalyst based at least on an amount of reductant stored in the catalyst and an amount of reductant in an exhaust gas mixture entering the catalyst; and    providing an indication of degradation based on a comparison of said actual exotherm and said expected exotherm.    
   
   
       2 . The method as set forth in  claim 1  wherein the NOx-reducing catalyst in an ALNC.  
   
   
       3 . The method as set forth in  claim 1  wherein the NOx-reducing catalyst is an oxidation catalyst.  
   
   
       4 . The method as set forth in  claim 1  wherein said reductant is hydrocarbon.  
   
   
       5 . The method as set forth in  claim 4  further comprising adjusting an amount of reductant injection into said NOx-reducing catalyst in response to said indication of degradation.  
   
   
       6 . A diagnostic system, comprising: 
 a NOx-reducing catalyst coupled downstream of an internal combustion engine; and    a controller introducing reductant into an exhaust gas mixture entering said NOx-reducing catalyst, said controller further calculating an amount of reductant stored in said NOx-reducing catalyst, and estimating an exotherm across said Nox-reducing catalyst based at least on said amount of reductant stored in said NOx-reducing catalyst and on an amount of reductant in said exhaust gas mixture entering said NOx-reducing catalyst.    
   
   
       7 . The system as set forth in  claim 6  further comprising a second temperature sensor providing a measurement of a NOx-reducing catalyst inlet temperature.  
   
   
       8 . The system as set forth in  claim 7  wherein said controller further calculates an actual exotherm across said NOx-reducing catalyst based on said inlet and outlet temperature measurements.  
   
   
       9 . The system as set forth in  claim 8  wherein said reductant is hydrocarbon.  
   
   
       10 . The system as set forth in  claim 9  wherein said controller further estimates said exotherm across said NOx-reducing catalyst based on said inlet temperature measurement.  
   
   
       11 . The system as set forth in  claim 10  wherein said controller further compares said estimated and said actual exotherm and provides an indication of degradation based on said comparison.  
   
   
       12 . The system as set forth in  claim 11  wherein said controller further adjusts an amount of reductant introduced into said exhaust gas mixture entering said NOx-reducing catalyst based on said indication of degradation.  
   
   
       13 - 16 . (canceled)  
   
   
       17 . The method as set forth in  claim 6  wherein said NOx-reducing catalyst is an ALNC.  
   
   
       18 . The method as set forth in  claim 6  wherein said NOx-reducing catalyst is an oxidation catalyst.  
   
   
       19 - 21 . (canceled)  
   
   
       22 . An article of manufacture comprising: 
 a computer storage medium having a computer program encoded therein for use with an emission control system for an internal combustion engine, said emission control system including at least a NOx-reducing catalyst, said computer program comprising: 
 code for providing an indication of an operating condition;  
 code for increasing an amount of reductant in an exhaust gas mixture entering the NOx-reducing catalyst by a predetermined value in response to said indication;  
 code for calculating an expected change in a catalyst temperature based on said predetermined increased reductant injection amount and on a thermodynamic model of the NOx-reducing catalyst, wherein said model takes into account at least an amount of reductant stored in the catalyst.  
   
   
   
       23 . The system as set forth in  claim 22  wherein said operating condition is catalyst light-off.  
   
   
       24 . The system as set forth in  claim 23  wherein said NOx-reducing catalyst is an ALNC.  
   
   
       25 . The system as set forth in  claim 23  wherein said NOx-reducing catalyst is an oxidation catalyst.  
   
   
       26 . The system as set forth in  claim 22  wherein said thermodynamic model further takes into account a NOx-reducing catalyst age.