Strategy for scheduling LNT regeneration

Abstract

A lean NO X trap is a diesel exhaust aftertreatment system is selectively denitrated when a measure relating to NO X loading, remaining NO X storage capacity, or performance of the exhaust aftertreatment system or a portion thereof comprising the lean NO X trap reaches a critical value. The critical value is determined based in part on conduciveness of current conditions to regenerating the lean NO X trap. Accordingly, denitration is scheduled based on a balance between the urgency of the need to regenerate and conduciveness of current conditions to regeneration. The stopping point for regeneration can also be selected based on conduciveness of current conditions to regeneration. The method maintains exhaust aftertreatment performance while reducing regeneration fuel penalty.

1 . A method of operating a power generation system, comprising:
 operating a diesel engine to produce a lean exhaust comprising NO X ;   passing the lean exhaust through an exhaust aftertreatment system comprising a lean NO X  trap that adsorbs a portion of the NO X  from the exhaust; and   selectively denitrating the lean NO X  trap based on balancing between a first factor relating to the state and or performance of the exhaust aftertreatment system or a portion thereof comprising the lean NO X  trap and a second factor relating to the conduciveness of current conditions to regenerating the lean NO X  trap with a low fuel penalty;   wherein denitrating the lean NO X  trap comprises providing an overall rich exhaust-reductant mixture to the lean NO X  trap, whereby the lean NO X  trap releases and reduces stored NO X .   
   
   
       2 . The method of  claim 1 , wherein the conduciveness of current conditions to regenerating the lean NO X  trap with a low fuel penalty is assessed based in part on an exhaust oxygen concentration. 
   
   
       3 . The method of  claim 1 , wherein the conduciveness of current conditions to regenerating the lean NO X  trap with a low fuel penalty is assessed based in part on an exhaust oxygen flow rate. 
   
   
       4 . The method of  claim 1 , wherein the conduciveness of current conditions to regenerating the lean NO X  trap with a low fuel penalty is assessed based in part on an exhaust flow rate. 
   
   
       5 . The method of  claim 1 , wherein the conduciveness of current conditions to regenerating the lean NO X  trap is determined based at least in part on a engine speed-load information. 
   
   
       6 . The method of  claim 1 , wherein:
 the first factor is assigned a first numerical value;   the second factor is assigned a second numerical value; and   the selection of whether or not to regenerate the lean NO X  trap is based on a numerical comparison involving the first and second values.   
   
   
       7 . The method of  claim 1 , wherein the first factor is determined from a measured performance of the exhaust aftertreatment system or a portion thereof. 
   
   
       8 . The method of  claim 1 , wherein the first factor is determined from a NO X  loading or remaining storage capacity of the lean NO X  trap. 
   
   
       9 . The method of  claim 1 , wherein a stopping point for denitration is selected based on conduciveness of current conditions to regenerating the lean NO X  trap with a low fuel penalty 
   
   
       10 . The method of  claim 9 , wherein the stopping point for denitration relates to NO X  loading or remaining storage capacity of the lean NO X  trap 
   
   
       11 . A method of operating a power generation system, comprising:
 operating a diesel engine to produce a lean exhaust comprising NO X ;   passing the lean exhaust through an exhaust aftertreatment system comprising a lean NO X  trap that adsorbs a portion of the NO X  from the exhaust; and   selectively denitrating the lean NO X  trap when a measure relating to NO X  loading, remaining NO X  storage capacity, or performance of the exhaust aftertreatment system or a portion thereof comprising the lean NO X  trap reaches a critical value;   wherein the critical value is determined based in part on conduciveness of current conditions to regenerating the lean NO X  trap; and   denitrating the lean NO X  trap comprises providing an overall rich exhaust-reductant mixture to the lean NO X  trap, whereby the lean NO X  trap releases and reduces stored NO X .   
   
   
       12 . The method of  claim 11 , wherein the critical value depends on an exhaust oxygen concentration. 
   
   
       13 . The method of  claim 11 , wherein the critical value depends on an exhaust oxygen flow rate. 
   
   
       14 . The method of  claim 11 , wherein the critical value depends on an exhaust flow rate. 
   
   
       15 . The method of  claim 11 , wherein the critical value is determined based on engine speed-load information. 
   
   
       16 . The method of  claim 11 , wherein the critical value is for a measure of performance of the exhaust aftertreatment system or a portion thereof. 
   
   
       17 . The method of  claim 11 , wherein the critical value is for NO X  loading or remaining storage capacity of the lean NO X  trap. 
   
   
       18 . The method of  claim 11 , wherein a critical value for terminating denitration is determined based in part on conduciveness of current conditions to regenerating the lean NO X  trap 
   
   
       19 . The method of  claim 18 , wherein the critical value for terminating denitration relates to NO X  loading or remaining storage capacity of the lean NO X  trap