Exhaust gas purification system

Abstract

An exhaust gas purification system having a diesel particulate filter to purify particulate matter in the exhaust gas G from a diesel engine, wherein a an exhaust gas passage prevention structure or the like is installed in portions where particulate matter in the exhaust gas is collected and accumulated easily, and, the temperature raises easily by the oxidation of accumulated particulate matter, in said diesel particulate filter. The allows to avoid DPF melting damage or breakage, by equalizing the heat distribution of the diesel particulate filter (DPF) and preventing an abnormally high temperature from generating partially, and an exhaust gas purification system of excellent endurance can be provided.

What is claimed is:  
     
         1 . An exhaust gas purification system having a diesel particulate filter to purify particulate matter in the diesel engine exhaust gas, composed of an exhaust gas passage prevention structure installed in a portion where the PM in the exhaust gas is collected and accumulated easily and, at the same time, the temperature raises easily by oxidation of the accumulated PM, in said diesel particulate filter.  
     
     
         2 . The exhaust gas purification system of  claim 1 , wherein said diesel particulate filter is a wall flow type filter having a number of exhaust gas passages whose periphery is formed of porous wall surface and inlet side and outlet side of the exhaust gas passage sealed in zigzag, and said exhaust gas passage prevention structure is installed against said exhaust gas passage of the central portion of the exhaust gas inflow cross-section of said filter and, at the same time, said exhaust gas passage prevention structure is stop sealed both at the upstream side and the downstream side of said exhaust gas passage.  
     
     
         3 . The aforementioned exhaust gas purification system of  claim 1 , wherein said diesel particulate filter is a wall flow type filter having a number of exhaust gas passages whose periphery is formed of porous wall surface and inlet side and outlet side of the exhaust gas passage sealed in zigzag, and said exhaust gas passage prevention structure is installed against said exhaust gas passage of the central portion of the exhaust gas inflow cross-section of said filter and, at the same time, said exhaust gas passage prevention structure is made solid without the exhaust gas passage.  
     
     
         4 . An exhaust gas purification system having a diesel particulate filter to purify particulate matter in the diesel engine exhaust gas, composed of a heat absorber installed in a portion where the PM in the exhaust gas is collected and accumulated easily and, at the same time, the temperature raises easily by oxidation of the accumulated PM, in said diesel particulate filter, or in a surrounding portion of the portion.  
     
     
         5 . The exhaust gas purification system of  claim 4 , wherein said diesel particulate filter is a wall flow type filter having a number of exhaust gas passages whose periphery is formed of porous wall surface and inlet side and outlet side of the exhaust gas passage sealed in zigzag, and wherein said heat absorber is formed of a thick porous wall surface in the central portion of the exhaust gas inflow cross-section of said filter or the thick porous wall surface surrounding the central portion.  
     
     
         6 . An exhaust gas purification system having a diesel particulate filter to purify particulate matter in the diesel engine exhaust gas, composed of a heat diffusing member, presenting a higher heat conductivity than the diesel particulate filter, disposed in contact with a portion where the PM in the exhaust gas is collected and accumulated easily and, at the same time, the temperature raises easily by oxidation of the accumulated PM, in said diesel particulate filter.  
     
     
         7 . The exhaust gas purification system of  claim 6 , wherein said heat diffusing member is composed using metal, silicon nitride, and silicon carbide as material.  
     
     
         8 . The exhaust gas purification system of  claim 6  or  7 , wherein said diesel particulate filter is a wall flow type filter having a number of exhaust gas passages whose periphery is formed of porous wall surface and upstream side and downstream side of the exhaust gas passage sealed in zigzag, and wherein said heat diffusing member is composed of a stop sealing plate for sealing said downstream side in zigzag.  
     
     
         9 . The exhaust gas purification system of  claim 6  or  7 , wherein said heat diffusing member is composed of a member having a filter function.  
     
     
         10 . The exhaust gas purification system of  claim 9 , wherein both of said diesel particulate filter and said heat diffusing member are composed of a wall flow type filter having a number of exhaust gas passages whose periphery is formed of porous wall surface, and wherein the upstream side and the downstream side of said exhaust gas passage are sealed in zigzag.  
     
     
         11 . An exhaust gas purification system having a diesel particulate filter to purify particulate matter in the exhaust gas from a diesel engine by using a catalyst, wherein the oxidation power of said catalyst to be disposed in the diesel particulate filter is composed so as to decrease in order, step-wise or continuously, from the upstream to the downstream of the diesel particulate filter.  
     
     
         12 . An exhaust gas purification system having a diesel particulate filter to purify particulate matter in the exhaust gas from a diesel engine by using a catalyst, wherein the oxidation power of said catalyst to be disposed in the diesel particulate filter is composed so as to decrease in order, step-wise or continuously, from the outer periphery towards the center side of the diesel particulate filter.  
     
     
         13 . An exhaust gas purification system having a diesel particulate filter to purify particulate matter in the exhaust gas from a diesel engine by using a catalyst, wherein the oxidation power of said catalyst to be disposed in the diesel particulate filter is composed so as to decrease in order, step-wise or continuously, from the outer periphery of the upstream end towards the central portion of the downstream end of the diesel particulate filter.  
     
     
         14 . The exhaust gas purification system of one of  claims 11  to  13 , wherein the oxidation power of said catalyst is changed in three or more stages, or, continuously and, at the same time, the portion of the lowest oxidation power of said catalyst is formed by not disposing said catalyst.  
     
     
         15 . The exhaust gas purification system of one of  claims 11  to  14 , wherein said diesel particulate filter is a wall flow type filter having a number of exhaust gas passages whose periphery is formed of porous wall surface and, an inlet side and an outlet side of an exhaust gas passage sealed in zigzag.  
     
     
         16 . An exhaust gas purification system comprising an oxidation catalyst converter in the upstream of the exhaust gas passage and a diesel particulate filter to purify particulate matter in the exhaust gas from a diesel engine in the downstream, wherein said oxidation catalyst converter and said diesel particulate filter are formed into a cylinder-shape in which the exhaust gas enters in the upstream end portion and exits from the downstream end portion and, at the same time, it is so composed that the outer peripheral passage portion of said oxidation catalyst converter supports a strong oxidation catalyst, and the central passage portion a weak oxidation catalyst respectively.  
     
     
         17 . An exhaust gas purification system having a diesel particulate filter to purify particulate matter in the exhaust gas from a diesel engine in the exhaust gas passage and disposing an oxidation catalyst in the exhaust gas passage of said diesel particulate filter, wherein the diesel particulate filter is formed into a cylinder-shape in which the exhaust gas enters in the upstream end portion and exits from the downstream end portion and, at the same time, it is so composed that the outer peripheral passage portion of the diesel particulate filter supports a strong oxidation catalyst, and the central passage portion of the diesel particulate filter supports a weak oxidation catalyst respectively.  
     
     
         18 . The exhaust gas purification system of  claim 16  or  17 , wherein said strong oxidation catalyst is made of a rear metal system oxidation catalyst, while said weak oxidation catalyst is made of an oxide system oxidation catalyst.  
     
     
         19 . The exhaust gas purification system of  claim 18 , the transversal cross-section area of the outer peripheral passage portion supporting said strong oxidation catalyst is made into 0.5 to 1.0 time of the transversal cross-section area of the central passage portion supporting said weak oxidation catalyst.  
     
     
         20 . The exhaust gas purification system of one of  claims 16  to  19 , wherein said diesel particulate filter is a wall flow type filter having a number of the exhaust gas passages whose periphery is formed of porous wall surface and an inlet side and an outlet side of the exhaust gas passage sealed in zigzag.  
     
     
         21 . An exhaust gas purification system, wherein the diesel particulate filter to purify particulate matter in the exhaust gas from an engine is composed of a wall flow type filter having an inlet side and an outlet side of a plurality of cells whose periphery is formed of porous wall surface sealed in zigzag, and wherein an outer peripheral passage is disposed in the outer peripheral portion of said diesel particulate filter and a central passage in the central portion respectively, and it is so composed that exhaust gas passes through the gas inlet passage, said outer peripheral passage, said cells, said central passage and the gas exit passage in this order.  
     
     
         22 . The exhaust gas purification system of  claim 21 , wherein the oxidation catalyst is disposed in said outer peripheral passage.  
     
     
         23 . The exhaust gas purification system of  claim 22 , wherein the oxidation catalyst is supported by a ceramic or metal honeycomb structure formed separately from the diesel particulate filter and the honeycomb structure is disposed in said outer peripheral passage, for disposing an oxidation catalyst in the outer peripheral passage.  
     
     
         24 . The exhaust gas purification system of one  claims 21  to  23 , wherein a relief valve is disposed at least one of a passage wall between an outside chamber communicating said outer peripheral passage with said cell and said gas exit passage, or a passage wall between an inside chamber communicating said cell and said central passage, and said gas inlet passage, so that the exhaust gas bypasses said filter, when the clogging of said filter progresses and increases the pressure.  
     
     
         25 . An exhaust gas purification system, wherein the diesel particulate filter to purify particulate matter in the exhaust gas from an engine is composed of a wall flow type filter having an inlet side and an outlet side of a plurality of cells whose periphery is formed of porous wall surface sealed in zigzag, and wherein an outer peripheral passage is disposed in the outer peripheral portion of said diesel particulate filter and a central passage in the central portion respectively, and it is so composed that exhaust gas passes through the gas inlet passage, said central passage, said cells, said outer peripheral passage and the gas exit passage in this order.  
     
     
         26 . The exhaust gas purification system of  claim 25 , wherein an oxidation catalyst is disposed in said central passage.  
     
     
         27 . The exhaust gas purification system of  claim 26 , wherein, the oxidation catalyst is supported by a ceramic or metal honeycomb structure formed separately from the diesel particulate filter and said honeycomb structure is disposed in said central passage, for disposing an oxidation catalyst in said central passage.  
     
     
         28 . The exhaust gas purification system of one of  claims 21  to  23 , wherein a relief valve is disposed at least one of a passage wall between an outside chamber communicating said cell and said outer peripheral passage and said gas inlet passage, or a passage wall between an inside chamber communicating said central passage and said cell, and said gas exit passage, so that the exhaust gas bypasses said filter, when the clogging of said filter progresses and increases the pressure.  
     
     
         29 . The exhaust gas purification system of one of  claim 21  to  28 , wherein a thermal insulation layer is disposed on the outer surface of said exhaust gas purification system.