Method of deciding on catalyst deterioration and means for deciding on catalyst deterioration in Nox purging system

Abstract

The present invention provides a method of deciding on catalyst deterioration in an exhaust gas decontamination system, which method enables making an accurate decision on the state of deterioration of catalyst caused by sulfur poisoning in a NOx purging system using a direct reduction type NOx catalyst in the purging of NOx from exhaust gas. In particular, a method of deciding on catalyst deterioration in a NOx purging system ( 10 ) comprising exhaust gas passage ( 2 ) and, arranged therein, direct reduction type NOx catalyst ( 3 ), wherein when the operating condition of engine ( 1 ) is within a deterioration decision zone and is of stationary operation, an exhaust gas for decision is generated and wherein when the concentration of NOx in exhaust gas (Cnox) resulting from pass of the exhaust gas for decision through the direct reduction type NOx catalyst ( 3 ) is not below prescribed decision level (Cnoxlim), the direct reduction type NOx catalyst ( 3 ) is judged as being deteriorated.

1 . A method of deciding on catalyst deterioration in a NOx purging system comprised of a direct reduction type NOx catalyst arranged in an exhaust gas passage in which a catalyst component reduces NOx to nitrogen and is also oxidized when an oxygen concentration in the exhaust gas of an engine is high and the catalyst component is reduced when the oxygen concentration in the exhaust gas is low, which comprises; 
 generating the exhaust gas for decision when an operating state of an engine is within a deterioration decision zone and is in a steady operation state, and    deciding that the direct reduction type NOx catalyst is deteriorated when the NOx concentration in the exhaust gas resulting from pass of the exhaust gas for decision through the direct reduction type NOx catalyst is not less than a prescribed reference value.    
   
   
       2 . The method of deciding on catalyst deterioration in the NOx purging system according to  claim 1 , which comprises; 
 deciding that the operating state of the engine is within a deterioration decision zone, when the quantity of the exhaust gas is not more than a prescribed reference quantity of exhaust gas and a catalyst temperature ranges between a prescribed lower limit temperature for decision and a prescribed upper limit temperature for decision.    
   
   
       3 . The method of deciding on catalyst deterioration in the NOx purging system according to  claim 1 , which comprises; 
 generating the exhaust gas for decision so that an air/fuel ratio of the exhaust gas becomes a value between the air/fuel ratio of the exhaust gas during the normal engine operation and the air/fuel ratio of the exhaust gas for regenerating the direct reduction type NOx catalyst.    
   
   
       4 . A means for deciding on catalyst deterioration in a NOx purging system comprised of a direct reduction type NOx catalyst arranged in an exhaust gas passage in which a catalyst component reduces NOx to nitrogen and is also oxidized when an oxygen concentration in the exhaust gas of an engine is high and the catalyst component is reduced when the oxygen concentration in the exhaust gas is low, which comprises; 
 a zone judgment means for judging whether an exhaust gas state is in a zone capable of performing a decision for the catalyst deterioration,    a steady operation judgment means for judging whether an engine operating state is in a steady operation state,    a decision exhaust gas generation means for generating an exhaust gas for decision, and    a NOx concentration judgment means for deciding that the direct reduction type NOx catalyst is deteriorated when the NOx concentration in the exhaust gas resulting from pass of the exhaust gas for decision through the direct reduction type NOx catalyst is higher than a prescribed reference value.    
   
   
       5 . The means for deciding on catalyst deterioration in a NOx purging system according to  claim 4 , wherein; 
 the zone judgment means decides that the operating state of the engine is within a deterioration decision zone, when the quantity of the exhaust gas is not more than a prescribed reference quantity of the exhaust gas and a catalyst temperature ranges between a prescribed lower limit temperature for decision and a prescribed upper limit temperature for decision.    
   
   
       6 . The means for deciding on catalyst deterioration in a NOx purging system according to  claim 4 , wherein; 
 the decision exhaust gas generation means generates the exhaust gas for decision in which an air/fuel ratio of the exhaust gas becomes a value between the air/fuel ration of the exhaust gas during the normal engine operation and the air/fuel ratio of the exhaust gas for regenerating the direct reduction type NOx catalyst.