Exhaust emission control device

Abstract

An exhaust emission control device is provided which can effectively regenerate a NO x absorption reduction catalyst even in a relatively low temperature region to improve NO x reduction ratio while minimizing deterioration of fuel economy. Incorporated in an exhaust pipe 4 through which exhaust gas 3 discharged from a diesel engine 1 via an exhaust manifold 2 flows is a reformer 8 having a fuel adding device 5, a heater 6 and a reforming catalyst 7. Arranged downstream of the reformer is a NO x absorption reduction catalyst 9.

1 . An exhaust emission control device comprising a reformer incorporated in an exhaust pipe through which exhaust gas from an engine flows, said reformer having a fuel adding device, a heater and a reforming catalyst, and a NO x -absorption reduction catalyst arranged downstream of the reformer. 
   
   
       2 . An exhaust emission control device as claimed in  claim 1 , wherein the heater in the reformer is constituted by an anterior oxidation catalyst unit with oxidation catalyst having heating function being evenly arranged. 
   
   
       3 . An exhaust emission control device as claimed in  claim 2 , wherein the anterior oxidation catalyst unit is a membrane metal heater comprising a strip-like metal membrane coated with oxidation catalyst and capable of temperature raising through application of current so as to serve as oxidation catalyst with heating function and an insulating alumina tape as oxidation catalyst, the metal membrane and the insulating tape being wound together spirally in an overlapping manner. 
   
   
       4 . An exhaust emission control device as claimed in claim  2 , wherein the anterior oxidation catalyst unit is a wire mesh heater comprising wire sheets coated with oxidation catalyst and capable of temperature raising through application of current so as to serve as oxidation catalyst with heating function and insulating alumina meshes as oxidation catalyst, the wire sheet and the insulating mesh being laminated alternately and plurally in a direction of flow of the exhaust gas. 
   
   
       5 . An exhaust emission control device as claimed in  claim 1 , wherein the heater in the reformer comprises an anterior oxidation catalyst unit with centrally arranged oxidation catalyst with heating function, a mixer being arranged between said anterior oxidation catalyst unit and the reforming catalyst.