Exhaust line of a diesel engine and desulfation method

Abstract

A method for desulfating an NOx trap of an exhaust line of a diesel engine, the method to extract during the operation of the engine at least one portion of the fixed sulphur compounds in the NOx trap. The method produces a reformate via a reformer device from the fuel of the engine, preheat the NOx trap via injection of the reformate in the flow of exhaust gases, in an injection point located downstream of the engine is upstream of the NOx trap, until a predetermined desulfation temperature is reached in the NOx trap, then bypasses the flow of exhaust gases from a bypass point of the exhaust line located upstream of the injection point, and continues the injection of reformate in the NOx trap to produce the desulfation, the richness of the mixture supplying the diesel engine not being affected in the method.

1 - 14 . (canceled) 
   
   
       15 . A method of desulfating a NOx trap of an exhaust line of a diesel engine, the method to extract, during operation of engine, at least a portion of sulfur compounds fixed in the NOx trap, the method comprising:
 producing a reformate via a reformer device from fuel of the engine;   preheating the NOx trap by injecting the reformate into a flow of the exhaust gases at an injection point situated downstream of the engine and upstream of the NOx trap, until a predetermined desulfation temperature is reached in the NOx trap; and then   branching off the flow of the exhaust gases from a branch point on the exhaust line situated upstream of the injection point, and continuing the injection of reformate into the NOx trap to achieve the desulfation;   and richness of the mixture supplying the diesel engine is not affected by performing the method.   
   
   
       16 . The method as claimed in  claim 15 , wherein a duration of the branching is predetermined, the duration of the branching being between 10 seconds and 20 minutes. 
   
   
       17 . The method as claimed in  claim 15 , wherein the duration of the preheating is predetermined. 
   
   
       18 . The method as claimed in  claim 15 , wherein duration of at least one of the preheating and/or branching is determined by a temperature measurement. 
   
   
       19 . The method as claimed in  claim 15 , wherein, at the end of the branching, the exhaust gases are redirected into the NOx trap and production of reformate is stopped. 
   
   
       20 . The method as claimed in  claim 15 , wherein a plurality of preheating and branching operations alternate in cycles, and the production of reformate is continued during the cycles. 
   
   
       21 . The method as claimed in  claim 15 , wherein the reformate is produced by a technique selected from partial oxidation reforming, steam reforming, or autothermal reforming. 
   
   
       22 . The method as claimed in  claim 15 , for simultaneously regenerating a particulate filter placed in the exhaust line downstream of the NOx trap, wherein, during the preheating the NOx trap, the flow rate of reformate is adjusted to reach a predetermined regeneration temperature downstream of the particulate filter, and during the desulfating the NOx trap, the exhaust gases are reintroduced into the exhaust line at a reinjection point situated downstream of the NOx trap and upstream of the particulate filter. 
   
   
       23 . A use of a method as claimed in  claim 22  in the regeneration of an exhaust line comprising two NOx traps mounted in parallel, a particulate filter mounted downstream of the two NOx traps, and a valve system for distributing flow of the exhaust gases between the two NOx traps, wherein use of a valve system for distributing the reformate leaving the reformer between two injection points arranged in parallel upstream of the first and the second NOx traps, respectively. 
   
   
       24 . The use as claimed in  claim 23 , wherein, during the regeneration of the particulate filter, each of the two NOx traps is alternately in a preheating phase and in a desulfation phase. 
   
   
       25 . The use as claimed in  claim 23 , wherein NOx purges of each NOx trap are carried out while the other NOx trap is in a desulfation phase by momentarily inverting the valve systems. 
   
   
       26 . An exhaust line of diesel engines comprising:
 a NOx trap;   a particulate filter arranged downstream of the NOx trap; and   a valve device upstream of the NOx trap and a branch pipe allowing the exhaust gases to bypass the NOx trap and to be reinjected upstream of the particulate filter, by presence of a reformer and by presence of a computer capable of controlling a method as claimed in  claim 22 .   
   
   
       27 . An exhaust line of diesel engines for implementing a method as claimed in  claim 23 , comprising:
 two NOx traps mounted in parallel, a particulate filter mounted downstream of the two NOx traps, and a valve system for distributing the flow of the exhaust gases between the two NOx traps;   a reformer, of a valve system for distributing the reformate leaving the reformer between two injection points arranged in parallel upstream of the first and the second NOx traps, respectively; and   a computer implementing the method.   
   
   
       28 . A method of regenerating a particulate filter of a diesel engine exhaust line as claimed in  claim 26 , comprising:
 producing a reformate via the reformer from fuel of the engine and injecting the reformate into the exhaust line downstream of the valve device;   branching the flow of the exhaust gases into the branch pipe and reinjecting the gases into the particulate filter; and   oxidizing the reformate via the exhaust gases at the active surface of the particulate filter.