Emission gas purification system

Abstract

An emission gas purification system is provided capable of making EM clearer and further improving NOx purification capacity. An emission gas purification system 1 is provided for an exhaust system of an engine 3 , and includes a purification unit 16 having a catalyst for purifying NOx according to an air-fuel ratio of an emission gas, and an air-fuel ratio control unit 2 adjusting the air-fuel ratio of the emission gas supplied to the purification unit 16 . The air-fuel ratio control unit 2 purifies the emission gas by setting the emission gas A/F to be near stoichiometric or rich by reducing an intake air mass in an air-fuel mixture.

1 . An emission gas purification system for an exhaust system of a compression ignition internal combustion engine, the system comprising:
 a purification unit provided with a catalyst for purifying NOx according to an air-fuel ratio of an emission gas; and   an air-fuel ratio control unit for adjusting the air-fuel ratio of the emission gas supplied to the purification unit, wherein   the air-fuel ratio control unit purifies the emission gas by setting the air-fuel ratio of the emission gas to be near stoichiometric or rich, by reducing a charge efficiency of an air-fuel mixture in a cylinder.   
   
   
       2 . The emission gas purification system according to  claim 1 , wherein
 the air-fuel ratio control unit further performs at least one of changing of a reflux rate of the emission gas and a throttling.   
   
   
       3 . The emission gas purification system according to  claim 1 , wherein
 the purification unit is provided with a catalyst portion as an active material for purifying NOx, the catalyst portion containing at least one noble metal selected from the group consisting of Pt, Pd, and Rh, as well as a material having oxygen storage capacity.   
   
   
       4 . The emission gas purification system according to  claim 2 , wherein
 the purification unit is provided with a catalyst portion as an active material for purifying NOx, the catalyst portion containing at least one noble metal selected from the group consisting of Pt, Pd, and Rh, as well as a material having oxygen storage capacity.   
   
   
       5 . The emission gas purification system according to  claim 3 , wherein
 the material having oxygen storage capacity is a composite oxide containing one of CeO 2  or Ce.   
   
   
       6 . The emission gas purification system according to  claim 3 , wherein
 the active material contains at least Rh and at least one of Pt and Pd.   
   
   
       7 . The emission gas purification system according to  claim 4 , wherein
 the active material contains at least Rh and at least one of Pt and Pd.   
   
   
       8 . The emission gas purification system according to  claim 5 , wherein
 the active material contains at least Rh and at least one of Pt and Pd.   
   
   
       9 . The emission gas purification system according to  claim 3 , wherein
 the catalyst portion comprises at least one porous oxidative product selected from the group consisting of Al 2 O 3 , SiO 2 , ZrO 2 , and zeolite, as a carrier.   
   
   
       10 . The emission gas purification system according to  claim 5 , wherein
 the catalyst portion comprises at least one porous oxidative product selected from the group consisting of Al 2 O 3 , SiO 2 , ZrO 2 , and zeolite, as a carrier.   
   
   
       11 . The emission gas purification system according to  claim 6 , wherein
 the catalyst portion comprises at least one porous oxidative product selected from the group consisting of Al 2 O 3 , SiO 2 , ZrO 2 , and zeolite, as a carrier.   
   
   
       12 . The emission gas purification system according to  claim 9 , wherein
 the carrier is a composite oxide having a perovskite structure.   
   
   
       13 . The emission gas purification system according to  claim 4 , wherein
 the carrier is a composite oxide having a perovskite structure.   
   
   
       14 . The emission gas purification system according to  claim 6 , wherein
 the carrier is a composite oxide having a perovskite structure.