Patent Publication Number: US-9416704-B2

Title: Exhaust gas treatment device of engine

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the invention 
     The present invention relates to an exhaust gas treatment device of an engine, and more particularly, to an exhaust gas treatment device of an engine capable of preventing thermal damage of matching surfaces of catalyst portions which configure a combustible gas catalyst. 
     (2) Description of Related Art 
     As a conventional exhaust gas treatment device of an engine, there is a device including a combustible gas generating catalyst and an exhaust gas treatment portion, in which combustible gas is produced by catalytic reaction which generates heat by a combustible gas generating catalyst, the combustible gas is mixed with exhaust gas which passes through an engine exhaust gas path, and exhaust gas heated by combustion of the combustible gas is supplied to the exhaust gas treatment portion (see Japanese Patent Application Laid-Open No. 2012-188971 (see  FIGS. 1 and 2 ), for example). 
     The exhaust gas treatment device of this kind has a merit that treatment carried out by the exhaust gas treatment portion can be facilitated by heat of the heated exhaust gas. 
     In the exhaust gas treatment device of Japanese Patent Application Laid-Open No. 2012-188971, the combustible gas generating catalyst includes an aggregate of a plurality of catalyst portions. 
     BRIEF SUMMARY OF THE INVENTION 
     &lt;&lt;Problem&gt;&gt; Matching surfaces of catalyst portions are prone to be thermally damaged. 
     According to the exhaust gas treatment device of Japanese Patent Application Laid-Open No. 2012-188971, the combustible gas generating catalyst includes the aggregate of the plurality of catalyst portions and a forming operation of the combustible gas generating catalyst is made easy, but matching surfaces of adjacent catalyst portions are thermally damaged in some cases. 
     It is an object of the present invention to provide an exhaust gas treatment device of an engine capable of preventing matching surfaces of catalyst portions configuring a combustible gas catalyst from being thermally damaged. 
     As a result of research, the present inventors of the present invention have confirmed that it is possible to prevent the matching surfaces from being thermally damaged by bringing the matching surfaces of the catalyst portions into tight contact with each other, and have achieved the present invention. 
     A reason thereof is estimated as follows. 
     That is, by bringing the matching surfaces of the catalyst portions into tight contact with each other, a gap between the matching surfaces becomes narrow, raw material of combustible gas which passes through the gap are reduced, catalyst combustion heat generated at the matching surfaces is reduced, and matching surfaces are prevented from being thermally damaged. 
     MEANS FOR SOLVING THE PROBLEM 
     A matter to define the invention is as follows. 
     As shown in  FIG. 1 , an exhaust gas treatment device of an engine comprising a combustible gas generating catalyst  2  and an exhaust gas treatment portion  10 , in which combustible gas  8  is produced by catalytic reaction which generates heat at the combustible gas generating catalyst  2 , the combustible gas  8  is mixed with exhaust gas  9  which passes through an engine exhaust gas path  4 , and the exhaust gas  9  heated by combustion of the combustible gas  8  is supplied to the exhaust gas treatment portion  10 , wherein 
     as illustrated in  FIGS. 3A, 3B and 4A to 4D , the combustible gas generating catalyst  2  includes an aggregate of a plurality of catalyst portions  2   a  and  2   a,  each of the catalyst portions  2   a  and  2   a  includes a matching surface  2   b  with respect to adjacent one of the catalyst portions  2   a  and  2   a,    
     a fastening ring  11  is fitted over the combustible gas generating catalyst  2  in which the matching surfaces  2   b  and  2   b  of the adjacent catalyst portions  2   a  and  2   a  are abutted against each other, and the matching surfaces  2   b  and  2   b  of the adjacent catalyst portions  2   a  and  2   a  are brought into tight contact with each other by a fastening force of the fastening ring  11 . 
     EFFECT OF THE INVENTION 
     It is possible to prevent matching surfaces of catalyst portions from being thermally damaged. 
     As illustrated in  FIGS. 3A, 3B and 4A to 4D , a fastening ring  11  is fitted over the combustible gas generating catalyst  2  in which the matching surfaces  2   b  and  2   b  of the adjacent catalyst portions  2   a  and  2   a  are abutted against each other, and the matching surfaces  2   b  and  2   b  of the adjacent catalyst portions  2   a  and  2   a  are brought into tight contact with each other by a fastening force of the fastening ring  11 . Therefore, it is possible to prevent the matching surfaces  2   b  and  2   b  of the catalyst portions  2   a  and  2   a  from being thermally damaged. 
     &lt;&lt;Effects&gt;&gt; It becomes easy to form the combustible gas generating catalyst. 
     As illustrated in  FIGS. 4A to 4D , since the combustible gas generating catalyst  2  includes an aggregate of the plurality of catalyst portions  2   a  and  2   a,  it becomes easy to form the combustible gas generating catalyst  2 . 
     It is possible to prevent matching surfaces of catalyst portions from being thermally damaged. 
     As shown in  FIG. 1 , liquid fuel  5  is used as a raw material  7  of the combustible gas  8  and as illustrated in  FIGS. 3A, 3B and 4A to 4D , the combustible gas generating catalyst  2  includes the plurality of catalyst portions  2   a  and  2   a  including the vertical matching surfaces  2   b  extending along a center axis  2   c  of the combustible gas generating catalyst  2 . Therefore, liquid fuel  5  swiftly flows through a gap  2   d  between the matching surfaces  2   b  and  2   b  by its own weight, the liquid fuel  5  does not stagnate in the gap  2   d,  and it is possible to prevent a case where the matching surfaces  2   b  and  2   b  of the catalyst portions  2   a  and  2   a  are thermally damaged by the stagnating liquid fuel  5 . 
     It is possible to prevent the matching surfaces of the catalyst portions from being thermally damaged. 
     As illustrated in  FIG. 3A , a gap  2   d  between the matching surfaces  2   b  and  2   b  of the catalyst portions  2   a  and  2   a  existing directly below an inlet  12  is covered with the guide plate  13  from above. Therefore, it is possible to prevent thermal damage of the matching surfaces  2   b  and  2   b  of the catalyst portions  2   a  and  2   a  existing directly below the inlet  12  into which raw materials  7  in the inlet  12  easily flow excessively. 
     &lt;&lt;Effects&gt;&gt; Producing efficiency of combustible gas is enhanced. 
     As illustrated in  FIG. 3A , the raw material  7  of the inlet  12  is diverted by the guide plate  13  in a peripheral direction of the guide plate  13 . Therefore, the raw materials  7  are dispersed into the entire combustible gas generating catalyst  2 , and producing efficiency of combustible gas  8  is enhanced. 
     It becomes easy to produce a combustible gas generating catalyst. 
     As illustrated in  FIGS. 4A to 4D , the two catalyst portions  2   a  and  2   a  have the same shapes. Therefore, it is possible to configure the combustible gas generating catalyst  2  using two parts which are formed by the same forming die, and it becomes easy to produce the combustible gas generating catalyst  2 . 
     It is possible to prevent an exhaust gas treatment portion  10  from being thermally damaged. 
     As illustrated in  FIG. 1 , an oxidation catalyst  3  is placed in the exhaust gas path  4 , the combustible gas  8  is catalytic burned by the oxidation catalyst  3 , the exhaust gas  9  heated by catalytic combustion by the oxidation catalyst  3  is supplied to the exhaust gas treatment portion  10  located downstream of the oxidation catalyst  3 . Therefore, it is possible to gently increase the temperature of exhaust gas  9  by catalytic combustion of the oxidation catalyst  3 , and it is possible to prevent the exhaust gas treatment portion  10  from being thermally damaged. 
     The function for preventing the matching surfaces of the catalyst portions from being thermally damaged becomes apparent. 
     As illustrated in  FIG. 1 , when PM accumulated on the oxidation catalyst  3  is burned and removed, highly ignitable combustible gas  8  is produced at the combustible gas generating catalyst  2  by catalytic reaction which has an amount of heat generation higher than that when catalyst is burned by the oxidation catalyst  3 , and there is a tendency that an amount of heat generation of the matching surfaces  2   b  and  2   b  of the catalyst portions  2   a  and  2   a  becomes high. Therefore, the matching surfaces  2   b  and  2   b  of the catalyst portions  2   a  and  2   a  tightly contact with each other, the function for preventing the matching surfaces  2   b  and  2   b  of the catalyst portions  2   a  and  2   a  from being thermally damaged becomes apparent. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
       In the drawings: 
         FIG. 1  is a schematic diagram of an exhaust gas treatment device of a diesel engine according to an embodiment of the present invention; 
         FIG. 2  is a vertical sectional side view of a combustible gas generating mixer used in the device shown in  FIG. 1 ; 
         FIG. 3A  is a sectional view taken along line IIIA-IIIA in  FIG. 2 ,  FIG. 3B  is a sectional view taken along line IIIB-IIIB in  FIG. 2 , and  FIG. 3C  is a sectional view taken along line IIIC-IIIC in  FIG. 2 ; 
         FIGS. 4A to 4D  are diagrams for describing a combustible gas generating catalyst used in the device shown in  FIG. 1 , wherein  FIG. 4A  is a plan view,  FIG. 4B  is a sectional view taken along line B-B in  FIG. 4A ,  FIG. 4C  is a top-down perspective view of the combustible gas generating catalyst as viewed from front and diagonally above, and  FIG. 4D  is a diagram for describing a method of mounting a fastening ring on the combustible gas generating catalyst; 
         FIG. 5  is a top-down perspective view of the combustible gas generating mixer as viewed from side and diagonally above; 
         FIG. 6A  is a plan view of the combustible gas generating mixer shown in  FIG. 2 , and  FIG. 6B  is a sectional view taken along line VIB-VIB in  FIG. 2 ; 
         FIG. 7A  is a diagram as viewed from a VIIA direction arrow shown in  FIG. 2 , and  FIG. 7B  is a sectional view taken along line B-B in  FIG. 7A ; 
         FIG. 8  is a diagram as viewed from a VIII direction arrow shown in  FIG. 7A ; and 
         FIG. 9  is a time chart of DPF regeneration and oxidation catalyst regeneration. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 to 9  are diagrams for describing an exhaust gas treatment device of an engine according to an embodiment of the present invention. In this embodiment, an exhaust gas treatment device of a diesel engine will be described. 
     A major configuration of the exhaust gas treatment device is as follows. 
     As shown in  FIG. 1 , the exhaust gas treatment device includes a combustible gas generating catalyst  2  and an exhaust gas treatment portion  10 , combustible gas  8  is produced by catalytic reaction which generates heat at a combustible gas generating catalyst  2 , the combustible gas  8  is mixed into exhaust gas  9  which passes through an engine exhaust gas path  4 , and the exhaust gas  9  heated by combustion of the combustible gas  8  is supplied to the exhaust gas treatment portion  10 . 
     The exhaust gas treatment portion  10  is a DPF  19 . The DPF  19  is an abbreviation of a diesel particulate filter. In the DPF  19 , PM included in exhaust gas  9  becomes trapped and is accumulated. If a PM accumulation estimate value of the DPF  19  reaches a predetermined regeneration start value, PM is incinerated and removed by heat of exhaust gas  9  which is heated by combustion of the gas  8 , and the DPF  19  is regenerated. As the exhaust gas treatment portion  10 , it is possible to use an exhaust gas cleaning catalyst such as SCR catalyst and NOx storage catalyst in addition to the DPF  19 . The SCR catalyst is an abbreviation of a selective catalytic reduction, and NOx is an abbreviation of nitrogen oxide. 
     A configuration of the combustible gas generating catalyst is as follows. 
     As shown in  FIGS. 3A, 3B and 4A to 4D , the combustible gas generating catalyst  2  includes the aggregate of the plurality of catalyst portions  2   a  and  2   a,  and each of the catalyst portions  2   a  and  2   a  includes the matching surface  2   b  with respect to the adjacent catalyst portion  2   a.    
     A fastening ring  11  is fitted over the combustible gas generating catalyst  2  at which the matching surfaces  2   b  and  2   b  of the adjacent catalyst portions  2   a  and  2   a  are abutted against each other, and the matching surfaces  2   b  and  2   b  of the adjacent catalyst portions  2   a  and  2   a  are brought into tight contact with each other by a fastening force of the fastening ring  11 . 
     Liquid fuel  5  is used as raw materials  7  of the combustible gas  8  as shown in  FIG. 1 . The combustible gas generating catalyst  2  includes the plurality of catalyst portions  2   a  and  2   a  including the matching surfaces  2   b  and  2   b  which are perpendicular to a center axis  2   c  of the combustible gas generating catalyst  2  as shown in  FIGS. 3A, 3B and 4A to 4D . 
     As shown in  FIG. 3A , an upper central portion of the combustible gas generating catalyst  2  is provided with an inlet  12  for raw materials  7  of combustible gas  8 , a guide plate  13  is placed on an inner bottom surface  12   a  of the inlet  12 , and a gap  2   d  between the matching surfaces  2   b  and  2   b  of the catalyst portions  2   a  and  2   a  existing directly below the inlet  12  is covered with the guide plate  13  from above. According to this, raw materials  7  at the inlet  12  are diverted into a peripheral direction thereof by the guide plate  13 . 
     As shown in  FIG. 2 , an insertion hole  15  is formed in the combustible gas generating catalyst  2  in a penetration manner. A temperature detecting portion  14   a  of a catalyst temperature detector  14  is inserted into the insertion hole  15 . A catalyst temperature detecting sensor using a thermistor or a thermocouple is used as the catalyst temperature detector  14 . 
     As shown in  FIGS. 4A to 4D , the combustible gas generating catalyst  2  includes the two catalyst portions  2   a  and  2   a.    
     As shown in  FIG. 3C , a center axis  15   a  of the insertion hole  15  intersects with the center axis  2   c  of the combustible gas generating catalyst  2  at right angles and is formed in a direction extending along a direction parallel to the matching surfaces  2   b  and  2   b  of the catalyst portions  2   a  and  2   a.  According to this, the two catalyst portions  2   a  and  2   a  have the same shapes. 
     As shown in  FIG. 4C , the combustible gas generating catalyst  2  is reversed conical in shape, and the catalyst portions  2   a  and  2   a  have such shapes that the combustible gas generating catalyst  2  is divided into two pieces along the center axis  2   c.    
     The fastening ring  11  is reversed conical in shape extending along a peripheral surface of the combustible gas generating catalyst  2 , and four engaging pawls  11  a project from a small-diameter side edge of the fastening ring  11 . 
     The catalyst portions  2   a  and  2   a  of the combustible gas generating catalyst  2  are formed by weaving iron chromium wires. The combustible gas generating catalyst  2  is divided into the two catalyst portions  2   a  and  2   a,  the catalyst portions  2   a  and  2   a  are pressed into the reversed conical shapes, and a rhodium catalyst component is supported by the iron chromium wire. 
     The fastening ring  11  is made of stainless steel. 
     As shown in  FIG. 4D , the fastening ring  11  is mounted on the combustible gas generating catalyst  2  in the following manner. 
     The matching surfaces  2   b  and  2   b  of the adjacent catalyst portions  2   a  and  2   a  are abutted against each other to form the combustible gas generating catalyst  2 , the fastening ring  11  is fitted over the combustible gas generating catalyst  2 , and the combustible gas generating catalyst  2  is placed on a placement stage  20  such that the small-diameter side of the combustible gas generating catalyst  2  is oriented upward. 
     Next, a conical surface  21   a  of a jig  21  downwardly presses the fastening ring  11  from outside, the matching surfaces  2   b  and  2   b  of the catalyst portions  2   a  and  2   a  are brought into tight contact with each other by a fastening force of the fastening ring  11 , the engaging pawls  11   a,    11  a are made to bite into peripheral surfaces of the catalyst portions  2   a  and  2   a  by a force of the fastening ring  11  which tries to return upward by an elastic force of the combustible gas generating catalyst  2 , and the fastening ring  11  is fixed to the combustible gas generating catalyst  2 . 
     As shown in  FIG. 1 , the oxidation catalyst  3  is placed on the exhaust gas path  4 , the combustible gas  8  is catalytic burned by the oxidation catalyst  3 , and exhaust gas  9  heated by the catalytic burn by the oxidation catalyst  3  is supplied to the exhaust gas treatment portion  10  located downstream of the oxidation catalyst  3 . 
     The oxidation catalyst  3  is a DOC  10 . The DOC is an abbreviation of a diesel oxidation catalyst. 
     As shown in  FIG. 1 , an igniter  16  is placed upstream of the oxidation catalyst  3  in terms of a flow of exhaust gas. If a predetermined amount of PM is accumulated on the oxidation catalyst  3 , highly ignitable combustible gas  8  is produced at the combustible gas generating catalyst  2  by catalytic reaction which has an amount of heat generation higher than that when catalyst is burned by the oxidation catalyst  3 , temperature of the exhaust gas  9  is increased by flaming combustion of the highly ignitable combustible gas  8  ignited by the igniter  16 , and the PM accumulated on the oxidation catalyst  3  is burned and removed by heat of this exhaust gas  9 . 
     Air-fuel mixture which is mixture of liquid fuel  5  and air  6  is used as raw materials  7  of combustible gas  8 . If a predetermined amount of PM is accumulated on the oxidation catalyst  3 , a control unit  17  sets a mixture ratio of air  6  in the air-fuel mixture sent to a combustible gas generator  1  higher than that when catalyst is burned by the oxidation catalyst  3 , and the highly ignitable combustible gas  8  is produced at the combustible gas generating catalyst  2  by catalytic reaction by which an amount of heat generation becomes higher. 
     The essential configuration of the exhaust gas treatment device is as described above. 
     Next, an entire configuration of the exhaust gas treatment device will be described. 
     As shown in  FIG. 1 , the exhaust gas treatment device includes the combustible gas generating mixer  22 , an exhaust gas treatment case  23  and the control unit  17 . 
     The combustible gas generating mixer  22  includes the combustible gas generator  1 , a combustible gas supply passage  24  and a combustible gas mixture passage  25 . 
     The oxidation catalyst  3  and the DPF  19  are accommodated in the exhaust gas treatment case  23 . 
     As shown in  FIG. 2 , the combustible gas generating mixer  22  is a casting block body in which the combustible gas generator  1 , the combustible gas supply passage  24  and the combustible gas mixture passage  25  are integrally formed together. 
     An external appearance of the combustible gas generating mixer  22  is as shown in  FIGS. 5, 6A, 7A and 8 . 
     As shown in  FIG. 2 , the combustible gas generator  1  includes a mixer portion  1   a  and a catalyst accommodating portion  1   b  located below the mixer portion  1   a,  a lid  1   d  is mounted, from above, on the mixer portion  1   a  such that a gasket  1   c  is sandwiched therebetween, a catalyst warming-up heater  26  is mounted on a boss  1   e  of the lid  1   d,  and a mixer chamber  1   f  is formed around the boss  1   e.  An electric heating glow plug is used as the catalyst warming-up heater  26 . 
     As shown in  FIG. 1 or 6B , liquid fuel  5  and air  6  are supplied from a fuel supply groove  27  and an air supply groove  28  provided in an upper surface of the mixer portion  1   a  to the mixer chamber  1   f  through a fuel supply port  27   a  and an air supply port  28   a  of the gasket  1   c,  the liquid fuel  5  and the air  6  are mixed in the mixer chamber  1   f  and become air-fuel mixture, and this becomes raw materials  7  of combustible gas  8 . 
     As shown in  FIG. 2 , the combustible gas generating catalyst  2  is accommodated in the catalyst accommodating portion  1   b.    
     As shown in  FIG. 2 , the combustible gas generating catalyst  2  is reversed conical in shape whose upper side has a greater diameter. As shown in  FIG. 3A , the inlet  12  is formed in an upper central portion of the combustible gas generating catalyst  2  such that the inlet  12  is downwardly recessed, an inner bottom surface  12   a  of the inlet  12  is provided with the guide plate  13 , a combustible gas generating starting catalyst  29  is accommodated in an upper portion of the guide plate  13 , and the catalyst warming-up heater  26  is inserted into the combustible gas generating starting catalyst  29 . The combustible gas generating starting catalyst  29  is a mat made of alumina fiber, and a rhodium catalyst component is supported by a surface of the combustible gas generating starting catalyst  29 . The combustible gas generating starting catalyst  29  has higher retention capacity of liquid fuel  5  than the combustible gas generating catalyst  2 . The guide plate  13  includes a flat plate made of stainless steel. 
     As shown in  FIG. 2 , heat insulation cushion materials  30  are respectively interposed between a peripheral surface of the combustible gas generating catalyst  2  and a peripheral wall of the catalyst accommodating portion  1   b  and between an upper surface of the combustible gas generating catalyst  2  and a bottom surface of the mixer portion  1   a.  The heat insulation cushion material  30  includes a mat made of alumina fiber. 
     The insertion hole  15  into which the temperature detecting portion  14   a  of the catalyst temperature detector  14  is inserted is formed in a lower portion of the combustible gas generating catalyst  2  in a penetration manner. A thermistor is used as the catalyst temperature detector  14 . The guide plate  13  is placed directly above the temperature detecting portion  14   a.    
     As shown in  FIG. 2 , the combustible gas supply passage  24  horizontally extends from a directly below portion of the catalyst accommodating portion  1   b.  A terminal end of the combustible gas supply passage  24  is provided with a gas nozzle  31 . The gas nozzle  31  projects into a secondary air mixing chamber  32 . As shown in  FIG. 7B , a secondary air supply passage  33  is provided in parallel to the combustible gas supply passage  24 , combustible gas  8  and secondary air  34  are supplied from the gas nozzle  31  and the secondary air supply passage  33  to the secondary air mixing chamber  32 , and the combustible gas  8  and the secondary air  34  are mixed with each other in the secondary air mixing chamber  32 . The combustible gas  8  is radially injected from the gas nozzle  31  in a radial direction of the secondary air mixing chamber  32 , and the secondary air  34  whirls around the gas nozzle  31 . 
     An igniter accommodating chamber  35  is placed downstream of the secondary air mixing chamber  32 , and the igniter  16  is placed in the igniter accommodating chamber  35 . An electric heating glow plug is used as the igniter  16 . The combustible gas  8  which flows into the igniter accommodating chamber  35  is ignited by the igniter  16  under a predetermined condition. 
     As shown in  FIGS. 6A and 7A , a radiator plate  16   b  is mounted on an outward projection  16   a  of the igniter  16  which projects outward of a wall  22   a  of the combustible gas generating mixer  22 . According to this, combustion heat of the combustible gas  8  transmitted to the igniter  16  is radiated through a radiator plate  16   b,  so that the igniter  16  is restrained from being thermally damaged. 
     As shown in  FIG. 6A , the radiator plate  16   b  is placed in a cooling wind passage  50  of an engine cooling fan (not shown), and cooling wind  51  which passes through the cooling wind passage  50  hits against the radiator plate  16   b.  The radiator plate  16   b  is bent into a U-shape, the outward projection  16   a  of the igniter  16  is surrounded by the radiator plate  16   b,  a ventilating inlet  16   c  of the radiator plate  16   b  is provided upstream of the cooling wind passage  50 , and a wind shielding wall  16   d  of the radiator plate  16   b  is provided downstream of the cooling wind passage  50 . 
     Air-exhaust ports  16   f  and  16   f  are provided in both side walls  16   e  and  16   e  of the radiator plate  16   b  extending from the wind shielding wall  16   d  toward upstream of the cooling wind passage  50 . 
     As shown in  FIGS. 6A and 7A , a ventilating gap  22   b  is formed in the wall  22   a  of the combustible gas generating mixer  22  into which the igniter  16  is inserted, a portion of an inserting portion  16   g  of the igniter  16  inserted into the wall  22   a  of the combustible gas generating mixer  22  is exposed into the ventilating gap  22   b,  the ventilating gap  22   b  is placed in the cooling wind passage  50 , cooling wind  51  passing through the cooling wind passage  50  flows into the ventilating gap  22   b,  and the cooling wind  51  hits against a portion of the inserting portion  16   g  of the igniter  16 . According to this, combustion heat of the combustible gas  8  transmitted to the igniter  16  is radiated to cooling wind  51  which passes through the ventilating gap  22   b,  so that the igniter  16  is restrained from being thermally damaged. 
     As shown in  FIG. 2 , a communication port  36  is provided above the igniter accommodating chamber  35 , and the igniter accommodating chamber  35  is in communication with the combustible gas mixture passage  25  through the communication port  36 . A flame holding plate  37  is provided on a terminal end of the igniter accommodating chamber  35  in a standing direction, an upper end of the flame holding plate  37  projects from the communication port  36  into the combustible gas mixture passage  25 , and the upper end of the flame holding plate  37  upwardly inclines toward downstream in terms of a flow of exhaust gas so that flame generated by the igniter  16  is not blown out by exhaust gas  9  which passes through the combustible gas mixture passage  25 . An ignition detector  38  is placed in the combustible gas mixture passage  25 . A thermistor is used as the ignition detector  38 . 
     As shown in  FIG. 1 , the combustible gas mixture passage  25  configures a portion of the engine exhaust gas path  4 , and the combustible gas mixture passage  25  is placed between a compressor outlet  39   a  of a supercharger  39  and an exhaust gas inlet  23   a  of the exhaust gas treatment case  23 . 
     As shown in  FIG. 1 , the oxidation catalyst  3  is accommodated in an upstream side of the exhaust gas treatment case  23  which configures a portion of the engine exhaust gas path  4 , and the DPF  19  is accommodated in a downstream side of the exhaust gas treatment case  23 . An oxidation catalyst component of the oxidation catalyst  3  is supported by a honeycomb-shaped ceramic carrier. The oxidation catalyst  3  is a flow-through monolith having cells  3   a,  both ends of the cells  3   a  are opened, and the exhaust gas  9  passes through the cells  3   a.    
     An oxidation catalyst component of the DPF  19  is supported by a honeycomb-shaped ceramic carrier. The DPF  19  is a wall-flow monolith having cells  19   a  and  19   a.  Ends of the adjacent cells  19   a  and  19   a  are alternately closed, exhaust gas  9  passes through a wall  19   b  between the adjacent cells  19   a  and  19   a,  and PM included in the exhaust gas  9  becomes trapped by the wall  19   b.  The PM is an abbreviation of particulate material. 
     As shown in  FIG. 1 , the exhaust gas treatment case  23  is provided with an exhaust gas temperature detector  40  of an oxidation catalyst inlet, an exhaust gas temperature detector  41  of a DPF inlet, and an exhaust gas temperature detector  42  of a DPF outlet. The combustible gas mixture passage  25  of the combustible gas generator  1  is provided with an exhaust gas pressure detector  43  on an upstream side of the oxidation catalyst. These detectors  40 ,  41 ,  42  and  43  are connected to the control unit  17 . The control unit  17  is an engine ECU. The ECU is an abbreviation of an electronic control unit. 
     Connected to the control unit  17  are the catalyst warming-up heater  26 , a fuel pump  45  for supplying liquid fuel  5  from a fuel tank  44  to the mixer portion  1   a,  a blower  46 , an air-adjusting solenoid valve  47  which adjusts a supply amount of air  6  from the blower  46  to the mixer portion  1   a,  a secondary air-adjusting solenoid valve  48  which adjusts a supply amount of secondary air  34  from the blower  46  to the secondary air mixing chamber  32 , the igniter  16  and the ignition detector  38 . 
     As shown in  FIG. 9 , when an estimated value of a total PM accumulation amount of the DPF  19  and the oxidation catalyst  3  reaches a predetermined regeneration necessary value, regenerating processing is permitted by the control unit  17 . The control unit  17  estimates the total PM accumulation amount based on exhaust gas pressure on the upstream side of oxidation catalyst by the exhaust gas pressure detector  43 . When regeneration is permitted, the control unit  17  determines at the same time whether this permission of regeneration is given to the DPF regeneration or to oxidation catalyst regeneration. As shown in  FIG. 9 , if an interval  49  from completion of last regeneration to permission of regeneration is equal to or longer than predetermined time, the control unit  17  determines that DPF regeneration is permitted, and if the interval  49  is shorter than the predetermined time, the control unit  17  determines that oxidation catalyst regeneration is permitted. 
     Substantially all of PM accumulated on the DPF  19  is removed by one time DPF regeneration processing or one time oxidation catalyst regeneration processing, but PM accumulated on the oxidation catalyst  3  is not completely removed even through a plurality of times of DPF regeneration processing, and PM is gradually accumulated. Therefore, if the interval  49  is shorter than the predetermined time, it is possible to estimate that a predetermined amount PM which requires regeneration is accumulated on the oxidation catalyst  3 . Hence, necessity of DPF regeneration and necessity of oxidation catalyst regeneration are distinguished depending on length of the interval  49 , and permission of DPF regeneration and permission of oxidation catalyst regeneration are determined. 
     As shown in  FIG. 1 , in both the cases of DPF regeneration and oxidation catalyst regeneration, when regeneration is started by the control unit  17 , combustible gas generating catalyst  2  is warmed up by a catalyst warming-up heater  26 , liquid fuel  5  and air  6  are supplied to the combustible gas generator  1 , air-fuel mixture is formed by the mixer portion  1   a , the air-fuel mixture is used as the raw materials, and combustible gas  8  is produced by catalytic reaction which generates heat at the combustible gas generating catalyst  2 . 
     When exhaust gas temperature of the oxidation catalyst inlet is equal to or higher than activation temperature of the oxidation catalyst  3  in the DPF regeneration, combustible gas  8  is mixed with exhaust gas  9  which passes through a combustible gas mixing passage  25  together with secondary air  34  without being ignited by the igniter  16  under control of the control unit  17 , the combustible gas  8  is catalytic burned by the oxidation catalyst  3  by secondary air  34  and air in exhaust gas  9 , and exhaust gas  9  heated by catalytic combustion by the oxidation catalyst  3  is supplied to the DPF  10  located downstream of the oxidation catalyst  3 . 
     If exhaust gas temperature of the oxidation catalyst inlet is less than the activation temperature of the oxidation catalyst  3  in the DPF regeneration, combustible gas  8  is flaming-burned by secondary air  34  by ignition of the igniter  16  under control of the control unit  17 , exhaust gas  9  passing through the combustible gas mixture passage  25  is heated by heat of this flaming combustion, and exhaust gas temperature of the oxidation catalyst inlet reaches the activation temperature of the oxidation catalyst  3 . If the oxidation catalyst  3  is warmed up, the flaming combustion is completed, the combustible gas  8  is mixed with the exhaust gas  9  which passes through the combustible gas mixture passage  25  together with secondary air  34  without being ignited by the igniter  16 , the combustible gas  8  is catalytic burned by the oxidation catalyst  3  by secondary air  34  and air in exhaust gas  9 , and exhaust gas  9  heated by catalytic combustion at the oxidation catalyst  3  is supplied to the DPF  10  located downstream of the oxidation catalyst  3 . 
     If a cumulative sum of time during which exhaust gas temperature of the DPF inlet exceeds predetermined temperature reaches a predetermined value, the DPF regeneration is completed. 
     Ignition by the igniter  16  and completion of flaming combustion are carried out in the following manner. 
     Ignition is carried out by the igniter  16  in such a manner that the igniter  16  is energized and heated based on control of the control unit  17 , and highly ignitable combustible gas  8  is produced by combustible gas generating catalyst  2 . As compared with lowly ignitable combustible gas  8  which burns catalyst by oxidation catalyst  3 , according to highly ignitable combustible gas  8 , a mixture ratio of air  6  in air-fuel mixture which is supplied to combustible gas generating catalyst  2  is set high, and highly ignitable combustible gas  8  is produced by catalytic reaction which has a high amount of heat generation. The flaming combustion is completed in such a manner that lowly ignitable combustible gas  8  is produced by combustible gas generating catalyst  2 , and flaming combustion is blown out by lowly ignitable combustible gas  8 . 
     Combustible gas  8  is produced in such a manner that feedback control is carried out for reducing a deviation between target temperature of combustible catalyst  2  and detection temperature detected by the catalyst temperature detector  14  based on control of the control unit  17 , and supply amounts of liquid fuel  5  and air  6  and a mixture ratio are adjusted. When highly ignitable combustible gas  8  is produced, the target temperature of combustible catalyst  2  is set high, and a mixture ratio of air  6  in air-fuel mixture becomes high. When lowly ignitable combustible gas  8  is produced, the target temperature of combustible catalyst  2  is set low, and the mixture ratio of air  6  in the air-fuel mixture becomes low. 
     Oxidation catalyst is regenerated in such a manner that combustible gas  8  is flaming-burned by secondary air  34  by ignition by the igniter  16  based on control of the control unit  17 , and exhaust gas  9  which passes through the combustible gas mixture passage  25  is heated by heat of the flaming combustion. Ignition by the igniter  16  is carried out in such a manner that the igniter  16  is energized and heated, and combustible gas generating catalyst  2  produces highly ignitable combustible gas  8 . As compared with lowly ignitable combustible gas  8  which catalytic burns by oxidation catalyst  3 , according to highly ignitable combustible gas  8 , a mixture ratio of air  6  in air-fuel mixture supplied to combustible gas generating catalyst  2  is set high, and the highly ignitable combustible gas  8  is produced by catalytic reaction which has a high amount of heat generation. If predetermined time is elapsed in a state where exhaust gas temperature of the oxidation catalyst inlet keeps reaching target temperature, regeneration of oxidation catalyst is completed. Target temperature of the exhaust gas catalyst inlet of regeneration of oxidation catalyst is higher than activation temperature of oxidation catalyst  3 . 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.