Exhaust emission purification system for internal combustion engine

Abstract

An exhaust emission purification system for an internal combustion engine, which can appropriately recover the cleanup performance of a NOx purification device that is disposed on the downstream side of a SOx absorbent is disclosed. The exhaust emission purification system is provided with a SOx trap 13, which is provided on an upstream side of a NOx purification device 17, and a SOx desorption temperature of the SOx trap 13 being higher than that of the NOx purification device 17; a sulfur purge determination portion 21 that determines whether to execute a sulfur purge, on the basis of the SOx concentration detected by a SOx sensor 16; a sulfur purge execution portion 22 that changes the exhaust gas into a high temperature reducing atmosphere, in cases where a sulfur purge determination portion 21 determines to execute a sulfur purge of the NOx purification device 17.

1 . An exhaust emission purification system for an internal combustion engine, comprising:
 a NOx absorbent catalyst disposed in an exhaust passage of the internal combustion engine, the absorbent absorbing NOx in exhaust gas;   a SOx absorbent disposed in an upstream side of the NOx absorbent catalyst in the exhaust passage, the absorbent absorbing SOx in the exhaust gas, and a SOx desorption temperature of the absorbent being higher than that of the NOx absorbent catalyst;   a SOx concentration detecting means for detecting SOx concentration in the exhaust gas that circulates between the SOx absorbent and the NOx absorbent catalyst in the exhaust passage;   a regeneration determination means for determining whether to execute a regeneration process for the NOx absorbent catalyst so as to desorb SOx that has been absorbed to the NOx absorbent catalyst, on the basis of the SOx concentration detected by the SOx concentration detecting means; and   a regeneration execution means for changing the exhaust gas into a high temperature reducing atmosphere in cases where the regeneration determination means determines to execute the regeneration process for the NOx absorbent catalyst.   
   
   
       2 . The exhaust emission purification system for an internal combustion engine according to  claim 1 , wherein the SOx absorbent does not substantially comprise precious metals. 
   
   
       3 . The exhaust emission purification system for an internal combustion engine according to  claim 1 , wherein a substrate of the SOx absorbent does not substantially comprise silica. 
   
   
       4 . The exhaust emission purification system for an internal combustion engine according to  claim 1 , wherein the NOx absorbent catalyst is a catalyst which generates ammonia and absorbs the generated ammonia when the air-fuel ratio of the exhaust gas is rich, and which reduces NOx to elements thereof with the absorbed ammonia when the air-fuel ratio of the exhaust gas is lean. 
   
   
       5 . The exhaust emission purification system for an internal combustion engine according to  claim 4 , wherein a three-way catalyst is disposed in an upstream side of the SOx absorbent in the exhaust passage. 
   
   
       6 . An exhaust emission purification system for an internal combustion engine, comprising:
 a NOx absorbent catalyst disposed in an exhaust passage of the internal combustion engine, the absorbent absorbing NOx in exhaust gas;   a SOx absorbent disposed in an upstream side of the NOx absorbent catalyst in the exhaust passage, the absorbent absorbing SOx in the exhaust gas, and a SOx desorption temperature of the absorbent being higher than that of the NOx absorbent catalyst;   a NOx concentration detecting means for detecting NOx concentration in the exhaust gas that circulates in a downstream side of the NOx absorbent catalyst in the exhaust passage;   a regeneration determination means for determining whether to execute a regeneration process for the NOx absorbent catalyst so as to desorb SOx that has been absorbed to the NOx absorbent catalyst, on the basis of the NOx concentration detected by the NOx concentration detecting means; and   a regeneration execution means for changing the exhaust gas into a high temperature reducing atmosphere in cases where the regeneration determination means determines to execute the regeneration process for the NOx absorbent catalyst.   
   
   
       7 . The exhaust emission purification system for an internal combustion engine according to  claim 6 , wherein the SOx absorbent does not substantially comprise precious metals. 
   
   
       8 . The exhaust emission purification system for an internal combustion engine according to  claim 6 , wherein a substrate of the SOx absorbent does not substantially comprise silica. 
   
   
       9 . The exhaust emission purification system for an internal combustion engine according to  claim 6 , wherein the NOx absorbent catalyst is a catalyst which generates ammonia and absorbs the generated ammonia when the air-fuel ratio of the exhaust gas is rich, and which reduces NOx to elements thereof with the absorbed ammonia when the air-fuel ratio of the exhaust gas is lean. 
   
   
       10 . The exhaust emission purification system for an internal combustion engine according to  claim 9 , wherein a three-way catalyst is disposed in an upstream side of the SOx absorbent in the exhaust passage. 
   
   
       11 . An exhaust emission purification system for an internal combustion engine, comprising:
 a NOx absorbent catalyst disposed in an exhaust passage of the internal combustion engine, the absorbent absorbing NOx in exhaust gas;   a SOx absorbent disposed in an upstream side of the NOx absorbent catalyst in the exhaust passage, the absorbent absorbing SOx in the exhaust gas, and a SOx desorption temperature of the absorbent being higher than that of the NOx absorbent catalyst;   an air-fuel ratio detecting means for detecting an air-fuel ratio in the exhaust gas that circulates in a downstream side of the NOx absorbent catalyst in the exhaust passage;   a regeneration determination means for determining whether to execute a regeneration process for the NOx absorbent catalyst so as to desorb SOx that has been absorbed to the NOx absorbent catalyst, on the basis of the air-fuel ratio detected by the air-fuel ratio detecting means; and   a regeneration execution means for changing the exhaust gas into a high temperature reducing atmosphere in cases where the regeneration determination means determines to execute the regeneration process for the NOx absorbent catalyst.   
   
   
       12 . The exhaust emission purification system for an internal combustion engine according to  claim 11 , wherein the SOx absorbent does not substantially comprise precious metals. 
   
   
       13 . The exhaust emission purification system for an internal combustion engine according to  claim 11 , wherein a substrate of the SOx absorbent does not substantially comprise silica. 
   
   
       14 . The exhaust emission purification system for an internal combustion engine according to  claim 11 , wherein the NOx absorbent catalyst is a catalyst which generates ammonia and absorbs the generated ammonia when the air-fuel ratio of the exhaust gas is rich, and which reduces NOx to elements thereof with the absorbed ammonia when the air-fuel ratio of the exhaust gas is lean. 
   
   
       15 . The exhaust emission purification system for an internal combustion engine according to  claim 14 , wherein a three-way catalyst is disposed in an upstream side of the SOx absorbent in the exhaust passage.