System and method for cleaning exhaust gas while avoiding nitrous oxide

Abstract

The present invention relates to a method for cleaning exhaust gas, and a correspondingly designed exhaust gas system. The present method, or the corresponding system, serves to avoid the formation of nitrous oxide as a secondary exhaust gas, which may primarily be created during the loading of specific catalyst types with NH 3 .

1 . Method for reduction of harmful automobile exhaust gas components with the aid of an exhaust gas system having at least two catalysts selected from the group consisting of NSC, TWC, and TWNSC, wherein the exhaust gas is diverted around the downstream catalyst of the at least two catalysts if this is within a temperature window in which it is capable of forming N 2 O from NH 3 , and the upstream catalyst of the at least two catalysts produces NH 3 . 
     
     
         2 . Method according to  claim 1 ,
 characterized in that   the exhaust gas is produced by a gasoline engine that is operated predominantly with an A/F mixture that is lean on average.   
     
     
         3 . Method according to  claim 1 ,
 characterized in that   the downstream catalyst of the at least two catalysts is selected from the group consisting of TWNSC and NSC.   
     
     
         4 . Method according to  claim 1 ,
 characterized in that   the exhaust gas system downstream of the at least two catalysts has at least one NOx reduction catalyst.   
     
     
         5 . Method according to  claim 4 ,
 characterized in that   the NOx reduction catalyst is made up of at least one SCR and/or NSC catalyst.   
     
     
         6 . Method according to  claim 5 ,
 characterized in that   the at least one SCR catalyst is arranged upstream of the at least one NSC catalyst.   
     
     
         7 . Method according to  claim 1 ,
 characterized in that   the diversion of the exhaust gas takes place when the downstream catalyst of the least two catalysts has a temperature of less than 350° C.   
     
     
         8 . Method according to  claim 1 ,
 characterized in that   the at least two catalysts are located in the first half of the exhaust gas tract, as measured from the motor output to the end of the exhaust pipe.   
     
     
         9 . Method according to  claim 1 ,
 characterized in that   at least one temperature sensor is located in the flow direction of the exhaust gas after the downstream catalyst of the at least two catalysts.   
     
     
         10 . Method according to  claim 1 ,
 characterized in that   at least one temperature sensor is located between the at least two catalysts.   
     
     
         11 . Method according to  claim 1 ,
 characterized in that   the diversion of the exhaust gas around the downstream catalyst of the at least two catalysts is effected by means of a device for activating and deactivating the diversion, which device is positioned at the merger of the diversion and the main exhaust gas tract.   
     
     
         12 . Method according to  claim 11 ,
 characterized in that   the device for activating and deactivating the diversion is a valve or an exhaust gas flap.   
     
     
         13 . System for exhaust gas aftertreatment, having at least two catalysts from the group consisting of NSC, TWC, and TWNSC, wherein the system is designed so that the exhaust gas may be diverted around the downstream catalyst of the at least two catalysts if this is capable of forming N 2 O from NH 3 . 
     
     
         14 . System according to  claim 13 ,
 characterized in that   the downstream catalyst of the at least two catalysts is selected from the group consisting of TWNSC and NSC.   
     
     
         15 . System according to  claim 13 ,
 characterized in that   the exhaust gas system downstream of the at least two catalysts has at least one NOx reduction catalyst.   
     
     
         16 . A method for the aftertreatment of the exhaust gas of a gasoline engine that is operated predominantly with an A/F mixture that is lean on average, comprising passing exhaust gas within the system of  claim 13 .