Exhaust Purification System of Internal Combustion Engine

Abstract

An engine exhaust passage is provided with a fuel addition valve ( 14 ) for adding fuel in the form of atomized drops, an oxidation catalyst ( 11 ), and an NO x storage and reduction catalyst ( 12 ) in that order. The oxidation catalyst ( 11 ) carries as a precious metal not only platinum Pt, but also palladium Pd. A molar ratio of the platinum Pt with respect to the sum of the platinum Pt and palladium Pd carried on the oxidation catalyst ( 11 ) is set to between about 50 percent to about 80 percent.

1 . An internal combustion engine providing a fuel addition device adding fuel in the form of atomized drops inside an engine exhaust passage, providing an oxidation catalyst inside the engine exhaust passage downstream of the fuel addition device, providing an NO x  storage and reduction catalyst storing the NO x  contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean and releasing the stored NO x  when the air-fuel ratio of the inflowing exhaust gas becomes a stoichiometric air-fuel ratio or rich inside the engine exhaust passage downstream of the oxidation catalyst, adding fuel from the fuel addition device when making the air-fuel ratio of the exhaust gas flowing into the NO x  storage and reduction catalyst rich so as to make the NO x  storage and reduction catalyst release NO x , and making the fuel added at this time deposit in the form of drops on the oxidation catalyst, wherein to make the fuel deposited in the form of drops on the oxidation catalyst vaporize, the oxidation catalyst carries as a precious metal not only platinum Pt, but also palladium Pd and the molar ratio of the platinum Pt with respect to the sum of the platinum Pt and palladium Pd carried on the oxidation catalyst is set from about 50 percent to about 80 percent.  
   
   
       2 . An exhaust purification system of internal combustion engine as set forth in  claim 1 , wherein a molar ratio of platinum Pt with respect to the sum of the platinum Pt and palladium Pd carried on the oxidation catalyst is set to about 58 percent to about 75 percent.  
   
   
       3 . An exhaust purification system of internal combustion engine as set forth in  claim 1 , wherein a carrier of the oxidation catalyst is comprised of a basic carrier including at least one element selected from an alkali earth or rare earth.  
   
   
       4 . An exhaust purification system of internal combustion engine as set forth in  claim 1 , wherein the NO x  storage and reduction catalyst is carried on a particulate filter.  
   
   
       5 . An internal combustion engine providing a fuel addition device adding fuel in the form of atomized drops inside an engine exhaust passage, providing an NO x  storage and reduction catalyst storing the NO x  contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean and releasing the stored NO x  when the air-fuel ratio of the inflowing exhaust gas becomes a stoichiometric air-fuel ratio or rich inside the engine exhaust passage downstream of the oxidation catalyst, adding fuel from the fuel addition device when making the air-fuel ratio of the exhaust gas flowing into the NO x  storage and reduction catalyst rich so as to make the NO x  storage and reduction catalyst release NO x , and making the fuel added at this time deposit in the form of drops on the NO x  storage and reduction catalyst, wherein to make the fuel deposited in the form of drops on the NO x  storage and reduction catalyst vaporize, the NO x  storage and reduction catalyst carries as a precious metal not only platinum Pt, but also palladium Pd and the molar ratio of the platinum Pt with respect to the sum of the platinum Pt and palladium Pd carried on the NO x  storage and reduction catalyst is set from about 50 percent to about 80 percent.  
   
   
       6 . An exhaust purification system of internal combustion engine as set forth in  claim 5 , wherein a molar ratio of platinum Pt with respect to the sum of the platinum Pt and palladium Pd carried on the NO x  storage and reduction catalyst is set to about 58 percent to about 75 percent.  
   
   
       7 . An exhaust purification system of internal combustion engine as set forth in  claim 5 , wherein the NO x  storage and reduction catalyst is carried on a particulate filter.