Patent Publication Number: US-2015082777-A1

Title: Exhaust purification device burner

Description:
TECHNICAL FIELD 
     The technique of the present disclosure relates to a burner for an exhaust purification device. The burner is applied to an exhaust purification device, which purifies exhaust gas from the engine, and raises the temperature of the exhaust gas. 
     BACKGROUND ART 
     Conventional diesel engines include, in the exhaust passage, a diesel particulate filter (DPF), which captures particulate matter (PM) contained in exhaust gas. In such a DPF, in order to maintain the function of capturing particulate matter, a regeneration process, in which particulate matter captured by the DPF is burnt, is performed. 
     For example, Patent Document 1 discloses an exhaust purification device, in which a burner is arranged upstream of a DPF. Exhaust gas with the temperature raised by the burner is sent to the DPF to regenerate the DPF. In the burner, fuel for the engine and air for combustion are introduced to a combustion area, which is the inside space of a tubular flame stabilizer, and mixture of the fuel and the air for combustion is produced. The air-fuel mixture is then burnt by ignition, and the temperature of the exhaust gas is raised. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Japanese Laid-Open Patent Publication No. 2011-185493 
       
    
     SUMMARY OF THE INVENTION 
     Problem that the Invention is to Solve 
     While an engine is cold, the temperature of a flame stabilizer and the temperature of gas in the combustion area are low relative to those after completion of warming-up of the engine. For this reason, when the regeneration process is performed while the engine is cold, unburned gas contained in the combustion gas increases compared to that after the completion of the warming-up of the engine. 
     It is an objective of the technique of the present disclosure to provide a burner for an exhaust purification device that reduces fuel discharged as unburned gas. 
     Means for Solving the Problems 
     To achieve the above objective, according to one aspect of the present disclosure, a burner for an exhaust purification device (an exhaust purification device burner) comprises a tubular flame stabilizer having a space in which air-fuel mixture of fuel and air is combusted and an ejection port for ejecting combustion gas, a tubular cover that surrounds the flame stabilizer, in which a gap is formed between an inner circumference face of the cover and an outer circumference face of the flame stabilizer, an exhaust pipe connected to the cover to deliver exhaust gas into the gap, and a partition portion arranged in the gap to partition the gap into an upstream exhaust chamber and a downstream exhaust chamber. The upstream exhaust chamber is connected to the exhaust pipe and the downstream exhaust chamber, and the downstream exhaust chamber is connected to the ejection port of the flame stabilizer. 
     According to the above aspect, exhaust gas flowing into the gap between the flame stabilizer and the cover takes a more complex route due to the partition portion. This increases the possibility for the exhaust gas to contact the flame stabilizer and raises the temperature of the flame stabilizer. Thus, the temperature of gas is more easily raised in the combustion area heated by the flame stabilizer. As a result, even in cold, the temperature of the flame stabilizer and the temperature of the gas in the combustion area are promptly raised, and fuel in the combustion area is more easily vaporized, so that the fuel discharged as unburned gas after being supplied to the combustion area is reduced. 
     Preferably, the flame stabilizer is shaped as a cylindrical tube, and the exhaust pipe extends in the tangential direction of the outer circumferential face of the flame stabilizer. 
     According to the above aspect, since the exhaust gas flowing into the upstream exhaust chamber more easily swirls around the flame stabilizer, the flows of the exhaust gas are more easily aligned in the upstream exhaust chamber in one direction. As a result, for example, compared to when the exhaust gas flowing into the upstream exhaust chamber is divided into flows in two directions by striking the circumference wall of the flame stabilizer, it is easier for the exhaust gas to contact the portion of the outer circumferential face of the flame stabilizer that defines the upstream exhaust chamber. For this reason, heat is efficiently transferred from the exhaust gas to the flame stabilizer. 
     Preferably, the exhaust pipe connects to an outer circumferential face of the cover at one location. 
     According to the above aspect, the exhaust gas is introduced to the upstream exhaust chamber from one location of the upstream exhaust chamber. For this reason, the exhaust gas more easily swirls around the flame stabilizer in the upstream exhaust chamber. As a result, compared to when an exhaust pipe communicates with the upstream exhaust chamber at a plurality of locations, the flows of the exhaust gas are more easily aligned in one direction in the upstream exhaust chamber. 
     Preferably, the partition portion protrudes from the outer circumferential face of the flame stabilizer toward the inner circumferential face of the cover and is coupled to the outer circumferential face of the flame stabilizer and the inner circumferential face of the cover. The partition portion is a partition wall that partitions the gap into the upstream exhaust chamber and the downstream exhaust chamber. The partition wall includes a communication hole that extends through the partition wall such that the upstream exhaust chamber communicates with the downstream exhaust chamber. 
     According to the above aspect, the exhaust gas that has flowed into the upstream exhaust chamber flows into the downstream exhaust chamber through the communication hole, which extends through the partition wall. In this case, after flowing along the outer circumferential face of the flame stabilizer, the exhaust gas strikes the partition wall and flows along the partition wall. The exhaust gas then flows in the depthwise direction of the partition wall (the direction in which the communication hole extends). For this reason, compared to when the exhaust gas flows from the upstream exhaust chamber to the downstream exhaust chamber without changing the direction, the exhaust gas flowing into the gap between the flame stabilizer and the cover takes a more complex route. 
     Preferably, a flow path cross-sectional area of the exhaust pipe is larger than a flow path cross-sectional area of the upstream exhaust chamber. 
     According to the above aspect, compared to when the flow path cross-sectional area of the exhaust pipe is smaller than the flow path cross-sectional area of the upstream exhaust chamber, expansion of the exhaust gas in the upstream exhaust chamber is suppressed. For this reason, the decrease in the temperature of the exhaust gas is reduced, and therefore, the efficiency of heat transfer from the exhaust gas to the flame stabilizer is increased. 
     Preferably, the burner for an exhaust purification device further comprises an ignition portion, which is arranged in the space in the flame stabilizer to ignite the air-fuel mixture. With respect to distances in the axial direction of the flame stabilizer, the distance between the partition portion and the ejection port is shorter than the distance between the ignition portion and the ejection port. According to the above aspect, with respect to distances in the axial direction of the flame stabilizer, compared to when the distance between the partition portion and the ejection port is long, the flame stabilizer has a larger outer circumferential face that defines the upstream exhaust chamber. This facilitates increasing the temperature of the flame stabilizer with the exhaust gas flowing in the upstream exhaust chamber. With this, the temperature of gas in the combustion area is more easily raised by being heated by the flame stabilizer. As a result, the ambient temperature is more easily raised near the ignition portion in the combustion area. 
     According to another aspect of the present disclosure, the burner further comprises a premixing portion, which is arranged in the space in the flame stabilizer and produces the air-fuel mixture, and an ignition portion, which is arranged in the space in the flame stabilizer and ignites the air-fuel mixture produced in the premixing portion. The distance between the ignition portion and the upstream exhaust chamber is shorter than the distance between the ignition portion and the downstream exhaust chamber. 
     According to the above aspect, the air-fuel mixture combusted in the combustion area is air-fuel mixture that is mixed in advance in the premixing portion. For this reason, compared to when air-fuel mixture is produced and combusted in the combustion area, the air-fuel mixture is more easily ignited, and the air-fuel mixture is efficiently combusted. Furthermore, since the temperature of the gas is raised near the ignition portion, the exhaust gas is efficiently utilized as heat for reducing production of unburned gas compared to when the temperature of the gas is raised at a distance from the ignition portion. As a result, it is possible to further suppress the discharge of fuel supplied to the combustion area as unburned gas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an exhaust purification device including a burner for an exhaust purification device according to a first embodiment; 
         FIG. 2  is a cross-sectional view taken along line  2 - 2  of  FIG. 1 ; 
         FIG. 3  is a graph that shows a relationship between elapsed time from cold start of an engine and an ambient temperature near an ignition point in a combustion area; 
         FIG. 4  is a schematic view of a burner for an exhaust purification device according to a second embodiment; 
         FIG. 5  is a cross-sectional view taken along line  5 - 5  of  FIG. 4 ; and 
         FIG. 6  is a cross-sectional view taken along line  6 - 6  of  FIG. 4 . 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     A burner for an exhaust purification device according to a first embodiment of the present disclosure will now be described with reference to  FIGS. 1 to 3 . First, the general configuration of an exhaust purification device including the burner for an exhaust purification device will be described with reference to  FIG. 1 . 
     As shown in  FIG. 1 , an exhaust purification device  10  for a diesel engine is arranged downstream of an exhaust pipe  11 , through which exhaust gas from the engine flows. The exhaust purification device  10  includes a tubular upstream cover  13  and a tubular downstream cover  14 , which are coupled to each other. The downstream cover  14  includes a diesel particulate filter  12  (hereinafter, referred to as a DPF  12 ), to which particulate matter contained in the exhaust gas adsorbs. 
     The DPF  12  has a honeycomb structure made of, e.g., a porous silicon carbide and captures particulate matter in the exhaust gas with the surface of the inner wall that defines the honeycomb structure. A burner for an exhaust purification device  15  (hereinafter, referred to as a burner  15 ) is mounted upstream of the DPF  12 , and carries out a regeneration process of the DPF  12  by raising the temperature of the exhaust gas flowing into the DPF  12 . 
     The upstream cover  13  is one of the components included in the burner  15 , and its circumference wall has a basal end fixed to a basal wall  17  of the flame stabilizer  16 . The upstream cover  13  is connected to an exhaust pipe  11 , through which the exhaust gas from the engine flows. 
     The flame stabilizer  16  of the burner  15  has a tubular shape with the basal wall  17 , and its circumference wall is surrounded by the upstream cover  13 . The flame stabilizer  16  includes a small diameter portion  18  and a large diameter portion  19 . The small diameter portion  18  has a smaller diameter than the diameter of the basal wall  17  and is fixed to the basal wall  17 . The large diameter portion  19  extends from the distal end of the small diameter portion  18  to an ejection port  16 A of the flame stabilizer  16  while increasing its diameter. The flame stabilizer  16  includes a combustion area  20  formed in a space surrounded by the circumference wall of the small diameter portion  18  and the circumference wall of the large diameter portion  19 . 
     An air supply pipe  26  is fixed to the basal wall  17  of the flame stabilizer  16  and guides a portion of intake air that flows through an intake pipe  25  in a state of being compressed by a compressor of a turbocharger as air for combustion to the combustion area  20 . An air valve  27  is attached to a portion of an air supply pipe  26 . A portion of the intake air flows into the combustion area  20  through the air supply pipe  26  when the air valve  27  is in the open state. 
     A fuel injection valve  21  is fixed to the basal wall  17  of the flame stabilizer  16  inside a part where the circumference wall of the small diameter portion  18  is fixed to the basal wall  17 . The fuel injection valve  21  is supplied with fuel by a fuel pump for supplying fuel to the engine (not shown). A distal end portion of the fuel injection valve  21 , which includes an injection port, is arranged in the combustion area  20 . The fuel injection valve  21  injects the fuel into the combustion area  20  to supply atomized fuel to the combustion area  20 . 
     A pair of spark plugs  22  is fixed to the basal wall  17  of the flame stabilizer  16  inside a part where the circumference wall of the small diameter portion  18  is fixed to the basal wall  17 . The spark plugs  22  are arranged such that ignition portions  22   a , which are distal end portions of the spark plugs  22 , surround the distal end portion of the fuel injection valve  21 . The spark plugs  22  generate sparks in the combustion area  20  to ignite air-fuel mixture of fuel and air for combustion at an ignition point  23 . This produces flame F in the combustion area  20 . 
     A annular partition wall  33  is fixed to the upstream cover  13  and the small diameter portion  18 . The partition wall  33  is a partition portion that partitions a gap formed between the inner circumferential face of the upstream cover  13  and the outer circumferential face of the flame stabilizer  16  into an upstream exhaust chamber  31  and a downstream exhaust chamber  32 . The upstream exhaust chamber  31  is located close to the basal wall  17  (basal end) of the flame stabilizer  16 . The downstream exhaust chamber  32  is located close to the ejection port  16 A (distal end) of the flame stabilizer  16 . In detail, the partition wall  33  projects from the outer circumferential face of the small diameter portion  18  of the flame stabilizer  16  toward the inner circumferential face of the upstream cover  13 , and the partition wall  33  is coupled to the inner circumferential face of the upstream cover  13  and the outer circumferential face of the small diameter portion  18 . The partition wall  33  is located closer to the distal end of the flame stabilizer  16  (ejection port  16 A) than the ignition portions  22   a  in the axial direction of the flame stabilizer  16 . In other words, with respect to distances in the axial direction of the flame stabilizer  16 , the distance between the partition wall  33  and the ejection port  16 A is shorter than the distance between the ignition portions  22   a  and the ejection port  16 A. The upstream exhaust chamber  31  communicates with the exhaust pipe  11  through an opening  34  formed in the upstream cover  13 . The downstream exhaust chamber  32  has an open end located opposite to the partition wall  33 . The partition wall  33  includes communication holes  35  formed at predefined intervals in the circumferential direction of the partition wall  33 . The communication holes  35  connect the upstream exhaust chamber  31  to the downstream exhaust chamber  32 . In other words, after the exhaust gas flowing through the exhaust pipe  11  passes through the upstream exhaust chamber  31 , the communication holes  35 , the downstream exhaust chamber  32  in order, the exhaust gas flows into the DPF  12 . In this case, when the flame F is formed in the combustion area  20 , the temperature of exhaust gas is raised by the flame F, and then the exhaust gas flows into the DPF  12 . 
     As shown in  FIG. 2 , the exhaust pipe  11  is shaped such that piping extending in the radial direction of the upstream cover  13  is offset toward the left of the upstream cover  13  and extends substantially in the tangential direction of the outer surface of the upstream cover  13 . For this reason, the exhaust gas flowing into the upstream exhaust chamber  31  from the exhaust pipe  11  partially flows into the downstream exhaust chamber  32  through the communication holes  35  included in the partition wall  33  while the exhaust gas flowing in the upstream exhaust chamber  31  forms a swirling flow that swirls around the small diameter portion  18  of the flame stabilizer  16  as illustrated by the arrows shown in  FIG. 2 . 
     The upstream exhaust chamber  31  is formed such that the swirling flow of the exhaust gas has a flow path area smaller than the flow path area of the exhaust pipe  11 . In other words, in  FIG. 1 , a portion surrounded by the small diameter portion  18 , the partition wall  33 , the upstream cover  13 , and the basal wall  17  is formed so as to have an area smaller than the flow path area of the exhaust pipe  11 . 
     Operation of the burner  15  configured as above will now be described with reference to  FIG. 3 . 
     In the burner  15 , the gap between the upstream cover  13  and the flame stabilizer  16  is partitioned by the partition wall  33  into the upstream exhaust chamber  31  and the downstream exhaust chamber  32 . The partition wall  33  includes the communication holes  35 , which connect the upstream exhaust chamber  31  to the downstream exhaust chamber  32 . In addition, the exhaust pipe  11  communicates with the upstream exhaust chamber  31 . 
     According to this configuration, the exhaust gas which has flowed through the exhaust pipe  11  passes through the upstream exhaust chamber  31 , the communication holes  35 , and the downstream exhaust chamber  32 . After that, the exhaust gas flows into the DPF  12 . For this reason, compared to when the partition wall  33  is not formed, the exhaust gas that has flowed into the gap between the upstream cover  13  and the flame stabilizer  16  takes a more complex route to flow out of the gap, and therefore, the possibility for the exhaust gas to contact the circumference wall of the flame stabilizer  16  is increased. This facilitates heating the flame stabilizer  16  with heat transferred from the exhaust gas and raising the temperature of gas in the combustion area  20  heated with the flame stabilizer  16 . 
     In other words, even when the engine is cold, the temperature of the flame stabilizer  16  and the temperature of the gas in the combustion area  20  are promptly raised. Furthermore, after raising the temperatures of the flame stabilizer  16  and the combustion area  20 , it is easier to maintain the raised temperatures. This facilitates vaporization of the fuel in the combustion area  20  when the engine is cold, thereby reducing the fuel discharged as unburned gas after being supplied to the combustion area  20 . 
     In the burner  15 , the exhaust pipe  11  is, as shown in  FIG. 2 , one pipe that is offset toward the left of the upstream cover  13  and extends substantially in the tangential direction of the outer circumferential face of the upstream cover  13 . For this reason, the exhaust gas flowing into the upstream exhaust chamber  31  forms a swirling flow that swirls around the small diameter portion  18 . According to this configuration, compared to when a plurality of exhaust gas pipes is connected to the upstream cover  13 , it is easier to generate a swirling flow in the upstream exhaust chamber  31 . In addition, compared to when the exhaust gas flowing into the upstream exhaust chamber  31  forms two flows divided by the flame stabilizer  16  by striking the circumference wall of the flame stabilizer  16 , it is easier for the exhaust gas to contact the entire surface of the portion of the circumference wall of the small diameter portion  18  that defines the upstream exhaust chamber  31 . As a result, heat is efficiently transferred from the exhaust gas to the flame stabilizer  16 . 
     In the burner  15 , the exhaust pipe  11  is attached to the upstream cover  13  at a position such that a swirling flow is generated in the upstream exhaust chamber  31 . For this reason, for example, compared to when a guide plate for guiding the exhaust gas flowing into the upstream exhaust chamber  31  is arranged in the upstream exhaust chamber  31  to generate a swirling flow in the upstream exhaust chamber  31 , a simpler configuration is employed to allow the exhaust gas to contact the entire surface of the portion of the circumference wall of the small diameter portion  18  that defines the upstream exhaust chamber  31 . 
     In the burner  15 , the flow path cross-sectional area of the exhaust pipe  11  is larger than the flow path cross-sectional area in the upstream exhaust chamber  31 . For this reason, compared to when the flow path cross-sectional area of the exhaust pipe  11  is smaller than the flow path cross-sectional area of the upstream exhaust chamber  31 , the volume of the upstream exhaust chamber  31  in the same flow path length is smaller, and therefore, expansion of the exhaust gas in the upstream exhaust chamber  31  is suppressed. This reduces the decrease in the temperature of the exhaust gas flowing in the upstream exhaust chamber  31 , thereby increasing the efficiency of heat transfer from the exhaust gas to the flame stabilizer  16 . 
     In the burner  15 , the partition wall  33  is arranged closer to the distal end of the flame stabilizer  16  than the ignition portions  22   a . For this reason, compared to when the partition wall  33  is arranged closer to the basal wall  17  of the flame stabilizer  16  than the ignition portions  22   a , the circumference wall of the flame stabilizer  16  that defines the upstream exhaust chamber  31  is enlarged so that the circumference wall surrounds the ignition point  23 . As a result, the temperature of the flame stabilizer  16  is more easily raised with the exhaust gas flowing in the upstream exhaust chamber  31 , and the ambient temperature is more easily raised near the ignition point  23  via the flame stabilizer  16 . 
       FIG. 3  shows a graph that shows a relationship between elapsed time t from cold start of the engine and an ambient temperature T in the combustion area. In  FIG. 3 , an example indicated by a solid line represents the aforementioned burner  15 . A comparison example indicated by a long dashed double-short dashed line represents a burner for an exhaust purification device in which the partition wall  33  is not formed and the exhaust pipe  11  is connected to the upstream cover  13  so as to face the large diameter portion  19 . The ambient temperature T is a temperature near the ignition point  23 , and an ignitable temperature T 1  is a temperature at which mixture of fuel and air can be ignited. 
     As shown in  FIG. 3 , in the burner  15  of the example, the ambient temperature T near the ignition point  23  reaches the ignitable temperature T 1  in elapsed time t 1 . In the burner for an exhaust purification device of the comparison example, the ambient temperature T near the ignition point  23  reaches the ignitable temperature T 1  in elapsed time t 2 , which is longer than the elapsed time t 1 . Thus, it is recognized that the burner  15  of the example has the ambient temperature T near the ignition point  23  to reach the ignitable temperature T 1  earlier than the burner of the comparison example. 
     As described above, the burner  15  according to the first embodiment provides the following advantages. 
     (1) Even in cold, the temperature of the flame stabilizer  16  and the temperature of gas in the combustion area  20  heated by the flame stabilizer  16  are promptly raised. In addition, after the temperature of the flame stabilizer  16  is raised, it is easier to maintain the raised temperatures of the flame stabilizer  16  and the gas in the combustion area  20 . This reduces fuel discharged as unburned gas after being supplied to the combustion area  20 . 
     (2) Since the swirling flow that swirls around the flame stabilizer  16  is generated in the upstream exhaust chamber  31 , it is easier for the exhaust gas to contact the entire surface of the portion of the circumference wall of the flame stabilizer  16  that defines the upstream exhaust chamber  31 , and heat is efficiently transferred from the exhaust gas to the flame stabilizer  16 . 
     (3) The exhaust pipe  11  is attached to the upstream cover  13  at the position such that a swirling flow is generated in the upstream exhaust chamber  31 . Thus, compared to when a member such as a guide plate is arranged in the upstream exhaust chamber  31 , a simpler configuration can be employed to allow the exhaust gas to contact the entire surface of the portion of the circumference wall of the flame stabilizer  16  that defines the upstream exhaust chamber  31 . 
     (4) The exhaust gas flowing into the upstream exhaust chamber  31  flows along the partition wall  33 , and then flows into the downstream exhaust chamber  32  through the communication holes  35  of the partition wall  33 . In this case, in order to flow from the upstream exhaust chamber  31  to the downstream exhaust chamber  32 , the exhaust gas needs to change the flowing direction so as to flow in the depthwise direction of the partition wall  33  after flowing along the face of the partition wall  33 . For this reason, compared to when the exhaust gas flows from the upstream exhaust chamber  31  to the downstream exhaust chamber  32  without changing the flowing direction of the exhaust gas, the exhaust gas takes a more complex route, and therefore, the efficiency of heat transfer from the exhaust gas to the flame stabilizer  16  is increased. 
     (5) The flow path cross-sectional area of the exhaust pipe  11  is larger than the flow path cross-sectional area of the upstream exhaust chamber  31 . Thus, compared to when the flow path cross-sectional area of the exhaust pipe  11  is smaller than the flow path cross-sectional area of the upstream exhaust chamber  31 , the volume in the upstream exhaust chamber  31  per the same flow path length is smaller than the volume in the exhaust pipe  11 , and therefore, expansion of exhaust gas in the upstream exhaust chamber  31  is suppressed. Accordingly, heat is efficiently transferred from the exhaust gas to the flame stabilizer  16 . 
     (6) The partition wall  33  is arranged closer to the ejection port  16 A of the flame stabilizer  16  than the ignition portions  22   a . Thus, compared to when the partition wall  33  is arranged closer to the basal wall  17  of the flame stabilizer  16  than the ignition portions  22   a , it is easier to raise the temperature of the flame stabilizer  16 . As a result, the temperature of gas in the combustion area  20  is more easily raised by being heated by the flame stabilizer  16 . 
     Second Embodiment 
     A burner for an exhaust purification device according to a second embodiment of the present disclosure will now be described with reference to  FIGS. 4 to 6 . The burner for an exhaust purification device  50  according to the second embodiment is primarily configured in the same way as the burner for an exhaust purification device according to the first embodiment. For this reason, in the second embodiment, parts different from the first embodiment will be described in detail, and parts with similar functions to those in the first embodiment will not be described in detail by assigning like reference characters. 
     As shown in  FIG. 4 , in the burner for an exhaust purification device  50  (hereinafter, simply referred to as a burner  50 ), the flame stabilizer  16  has a cylindrical tube shape that has a bottom and is opened toward the DPF  12 . The basal wall  17  in the flame stabilizer  16  closes the opening at the basal end of the small diameter portion  18  in the flame stabilizer  16  and extends radially outward from the portion fixed to the small diameter portion  18 . 
     A tubular outer tube  51  is fixed to the edge of the basal wall  17  of the flame stabilizer  16 . The outer tube  51  extends from the edge of the basal wall  17  toward the DPF  12 , and surrounds the entire small diameter portion  18  of the flame stabilizer  16 . The distal end portion of the outer tube  51 , which is the one of two ends that is located close to the DPF  12 , is fixed to an annular closing wall  53 . The distal end portion of the outer tube  51  is arranged closer to the basal wall  17  than the ejection port  16 A of the flame stabilizer  16 . An area between the outer circumferential face of the small diameter portion  18  and the inner circumferential face of the outer tube  51  is sandwiched and closed by the basal wall  17  and the closing wall  53 . 
     The closing wall  53  has an outer circumferential edge fixed to the tubular upstream cover  13 . The upstream cover  13  extends from the outer circumferential edge of the closing wall  53  toward the DPF  12  and surrounds the entire large diameter portion  19  of the flame stabilizer  16 . The gap between the outer circumferential face of the large diameter portion  19  and the inner circumferential face of the upstream cover  13  is opened toward the DPF  12 . The upstream cover  13  serves as a tubular cover that surrounds the flame stabilizer  16 . 
     The partition wall  33  is arranged in the gap between the outer circumferential face of the large diameter portion  19  and the inner circumferential face of the upstream cover  13 . The annular partition wall  33  resides along a periphery of the large diameter portion  19 . The partition wall  33  partitions the gap between the outer circumferential face of the large diameter portion  19  and the inner circumferential face of the upstream cover  13  in the axial direction of the flame stabilizer  16  into the upstream exhaust chamber  31  and the downstream exhaust chamber  32 . The upstream exhaust chamber  31  is a space connected to the exhaust pipe  11 , and the downstream exhaust chamber  32  is a space connected to the ejection port  16 A. The partition wall  33  has the communication holes  35 , which extend through the partition wall  33  to connect the upstream exhaust chamber  31  to the downstream exhaust chamber  32 . 
     As shown in  FIG. 5 , the outer circumferential face of the outer tube  51  is connected to the air supply pipe  26 , and a guide plate  54  is arranged on the inner circumferential face of the outer tube  51  near the outlet of the air supply pipe  26 . The guide plate  54  is positioned to be separated from the outlet of the air supply pipe  26  and to face the outlet. The area between the outer circumferential face of the small diameter portion  18  and the outer tube  51  is an introduction flow path  52 . The air for combustion that enters the introduction flow path  52  from the air supply pipe  26  is guided by the guide plate  54 , and turns along the outer circumferential face of the small diameter portion  18 . 
     The small diameter portion  18  has an end (basal end) fixed to the basal wall  17  and has a plurality of first introduction ports  55  extending through the small diameter portion  18  in a portion located near the basal end. The first introduction ports  55  line up at equal intervals in the circumferential direction of the small diameter portion  18 . The space surrounded by the flame stabilizer  16  is the combustion area  20 , and the first introduction ports  55  lead a portion of the air for combustion that has entered the introduction flow path  52  to the inside of the flame stabilizer  16 . 
     The portion of the small diameter portion  18  that is located closer to the ejection port  16 A than the first introduction ports  55  includes a plurality of second introduction ports  56 , which extends through the small diameter portion  18 . The second introduction ports  56  line up at equal intervals in the circumferential direction of the flame stabilizer  16 . The second introduction ports  56  lead the air for combustion that has entered the introduction flow path  52  to the inside of the flame stabilizer  16 . 
     As shown in  FIG. 6 , a raised piece  57  is formed at the opening edge of each first introduction port  55  by cutting a portion of the circumference wall of the small diameter portion  18  and raising the portion inward. The raised piece  57  guides air for combustion from the first introduction port  55  to the inside of the flame stabilizer  16 , and swirls the air for combustion inside the flame stabilizer  16 . The raised piece  57  swirls the air for combustion in the swirling direction of the air for combustion in the introduction flow path  52  inside the flame stabilizer  16 . 
     A fuel supply unit  58 , which supplies fuel to the inside of the flame stabilizer  16 , is fixed to the basal wall  17 . The distal end portion of the fuel supply unit  58 , which includes a supply port, is arranged inside the flame stabilizer  16 . The fuel supply unit  58  is connected to a fuel pump for supplying fuel to the engine through a fuel valve. Fuel is sent to the fuel supply unit  58  by the fuel pump when the fuel valve is opened. The fuel sent to the fuel supply unit  58  is vaporized in the fuel supply unit  58  and injected to the inside of the flame stabilizer  16 . 
     A coupling portion  60  is coupled to the portion of the inner circumferential face  16   b  of the small diameter portion  18  that resides between the first introduction ports  55  and the second introduction ports  56  in the flame stabilizer  16 . The coupling portion  60  includes a flange  61 , an insertion portion  62 , and a radially-narrowed portion  63 . The flange  61 , the insertion portion  62 , and the radially-narrowed portion  63  are integrated. 
     The flange  61  is annular and resides along the inner circumferential face  16   b  of the small diameter portion  18  and fixed to the entire inner circumferential face  16   b  of the small diameter portion  18  in the circumferential direction of the inner circumferential face  16   b . In the space surrounded by the flame stabilizer  16 , the flange  61  and the basal wall  17  define a first mixing chamber  71 . 
     Air for combustion enters the first mixing chamber  71  through the first introduction ports  55 , and fuel enters the first mixing chamber  71  from the fuel supply unit  58 . The air for combustion swirls around the axis of the flame stabilizer  16  and the fuel is injected toward the center of the swirling air for combustion so that the air for combustion and the fuel are mixed in the first mixing chamber  71 . 
     The insertion portion  62  has a tubular shape extending from the radially-narrowed portion  63  toward the ejection port  16 A and has a smaller diameter than the inner diameter of the flange  61 . The radially-narrowed portion  63  has a tubular truncated cone shape extending from the inner circumferential edge of the flange  61  toward the ejection port  16 A and couples the flange  61  with the insertion portion  62 . 
     A tubular first inner tube  64  is inserted into the insertion portion  62 . The basal end of the first inner tube  64 , which is the one of two ends that is located close to the basal wall  17 , is joined to the insertion portion  62 . The flange  61  of the coupling portion  60  is coupled to the inner circumferential face  16   b  of the flame stabilizer  16 , and the insertion portion  62  of the coupling portion  60  is coupled to the outer circumferential face  64   a  of the first inner tube  64 . The coupling portion  60  closes an area between the inner circumferential face  16   b  of the flame stabilizer  16  and the outer circumferential face  64   a  of the first inner tube  64 . The distal end of the first inner tube  64 , which is the one of two ends that is located close to the ejection port  16 A, is opened. 
     A tubular second inner tube  65  is arranged around the first inner tube  64  to surround the first inner tube  64 . The distal end portion of the first inner tube  64  is surrounded by the second inner tube  65 . The end (distal end) of the second inner tube  65  that is located close to the ejection port  16 A is positioned closer to the ejection port  16 A than the distal end of the first inner tube  64 . The end (basal end) of the second inner tube  65  that is located close to the basal wall  17  is positioned closer to the ejection port  16 A than the basal end of the first inner tube  64 . 
     The opening at the distal end of the second inner tube  65  is closed by a closing wall  66 . The basal end of the second inner tube  65  is fixed to the inner circumferential face of the small diameter portion  18  with an annular support plate  67 . 
     The inner circumferential edge of the support plate  67  is fixed to the entire outer circumferential face  65   a  of the second inner tube  65 . The outer circumferential edge of the support plate  67  is fixed to the entire inner circumferential face  16   b  of the flame stabilizer  16 . A plurality of communication passages  68  extends through the support plate  67  so that the space located closer to the ejection port  16 A than the support plate  67  communicates with the space located closer to the basal wall  17  than the support plate  67 . A wire mesh  69 , which covers the communication passages  68 , is attached to the support plate  67 . 
     The space surrounded by the inner circumferential face of the first inner tube  64  in the space surrounded by the flame stabilizer  16  forms a second mixing chamber  72 . The air-fuel mixture coming out of the first mixing chamber  71  enters the second mixing chamber  72 . 
     In the space surrounded by the flame stabilizer  16 , the space that is located closer to the ejection port  16 A than the second mixing chamber  72  and surrounded by the inner circumferential face of the second inner tube  65  and the closing wall  66  forms a third mixing chamber  73 . The air-fuel mixture coming out of the second mixing chamber  72  enters the third mixing chamber  73 . 
     In the space surrounded by the flame stabilizer  16 , the area between the outer circumferential face of the first inner tube  64  and the inner circumferential face of the second inner tube  65  forms a fourth mixing chamber  74 . The air-fuel mixture coming out of the third mixing chamber  73  enters the fourth mixing chamber  74 . 
     In the space surrounded by the flame stabilizer  16 , the area surrounded by the inner circumferential face  16   b  of the flame stabilizer  16 , the support plate  67 , and the coupling portion  60  forms a fifth mixing chamber  75 . The air-fuel mixture coming out of the fourth mixing chamber  74  enters the fifth mixing chamber  75 . 
     The spark plug  22  is fixed to the outer circumferential face of the outer tube  51 . The ignition portion  22   a  of the spark plug  22  projects inward of the flame stabilizer  16  from the inner circumferential face  16   b  of the flame stabilizer  16 . The ignition portion  22   a  is arranged in the space between the inner circumferential face of the small diameter portion  18  and the outer circumferential face  65   a  of the second inner tube  65  and positioned closer to the ejection port  16 A than the support plate  67  in the axial direction of the flame stabilizer  16 . The distance between the ignition portion  22   a  and the upstream exhaust chamber  31  in the axial direction of the flame stabilizer  16  is shorter than the distance between the ignition portions  22   a  and the downstream exhaust chamber  32 . 
     The first mixing chamber  71 , the second mixing chamber  72 , the third mixing chamber  73 , the fourth mixing chamber  74 , and the fifth mixing chamber  75  form one premixing chamber  70 , which serves as a premixing portion for producing air-fuel mixture. The space between the inner circumferential face  16   b  of the flame stabilizer  16  and the outer circumferential face  65   a  of the second inner tube  65  and the space located closer to the ejection port  16 A than the closing wall  66  in the flame stabilizer  16  form the combustion area  20 . The premixing chamber  70  and the combustion area  20  are comparted with a compartment portion including the second inner tube  65 , the closing wall  66 , and the support plate  67 . The air-fuel mixture produced in the premixing chamber  70  enters the combustion area  20  through the communication passages  68  and is then ignited by the ignition portion  22   a.    
     As described above, the burner  50  according to the second embodiment provides the following advantages in addition to the above advantages (1) to (5). 
     (7) Before entering the combustion area  20  to be combusted, fuel is mixed with air for combustion in advance in the premixing chamber  70 . For this reason, compared to the configuration in which air-fuel mixture is not produced in the premixing chamber  70 , it is easier to ignite the air-fuel mixture, and the air-fuel mixture is efficiently combusted. As a result, it is possible to further suppress the discharge of fuel supplied to the combustion area as unburned gas. 
     (8) The distance (shortest distance) between the ignition portions  22   a  and the upstream exhaust chamber  31  is shorter than the distance (shortest distance) between the ignition portion  22   a  and the downstream exhaust chamber  32 . Further, the temperature of the exhaust gas flowing in the upstream exhaust chamber  31  is transferred via the flame stabilizer  16 . This raises the temperature of gas near the ignition portion  22   a . Thus, compared to the configuration in which the temperature of gas is raised at a distance from the ignition portions  22   a , the exhaust gas is efficiently utilized as heat for reducing production of unburned gas. 
     (9) Before entering the first mixing chamber  71 , the air for combustion flowing in the introduction flow path  52  contacts the outer circumferential face of the flame stabilizer  16  and is heated with the outer circumferential face. As a result, it is easier to ignite the air-fuel mixture, and the air-fuel mixture is efficiently combusted. 
     (10) The outer circumferential face of the large diameter portion  19  defines the upstream exhaust chamber  31 . Thus, compared to the configuration in which the outer circumferential face of the small diameter portion  18  defines the upstream exhaust chamber  31 , the contact area of the outer circumferential face of the flame stabilizer  16  with the exhaust gas is enlarged. 
     The first and second embodiments may be modified in the following forms. 
     In the first embodiment, the partition wall  33  may be arranged closer to the basal wall  17  of the flame stabilizer  16  than the ignition portions  22   a . In other words, with respect to distances in the axial direction of the flame stabilizer  16 , the distance between the partition wall  33  and the ejection port  16 A may be longer than the distance between the ignition portions  22   a  and the ejection port. 
     In the second embodiment, the second introduction ports  56  may be omitted. In other words, air for combustion may be supplied to the combustion area  20  only through the premixing chamber  70 . 
     In the second embodiment, the air supply pipe  26  may be connected to the basal wall  17 . In other words, air for combustion may enter the premixing chamber  70  without traveling around the flame stabilizer  16 . 
     In the second embodiment, the compartment portion, which comparts the premixing chamber  70  and the combustion area  20 , may be, e.g., a flat plate arranged inside the flame stabilizer  16  to be orthogonal to the axial direction of the stabilizer  16 . In other words, the compartment portion, which comparts the premixing chamber  70  and the combustion area  20 , may be modified as long as it is configured as a member that partitions a space defined by the flame stabilizer  16  into a space producing air-fuel mixture and a space for igniting the air-fuel mixture (combustion area). 
     In the configuration in which the compartment portion includes the coupling portion  60 , the first inner tube  64 , the second inner tube  65 , the closing wall  66 , and the support plate  67 , a passage that connects the space for producing air-fuel mixture and the space for igniting the air-fuel mixture (combustion area) is complicated. For this reason, in view of mixing fuel and air for combustion to a great extent, it is preferable for the compartment portion to include the coupling portion  60 , the first inner tube  64 , the second inner tube  65 , the closing wall  66 , and the support plate  67 . 
     The distance between the ignition portion  22   a  and the upstream exhaust chamber  31  may be equal to the distance between the ignition portion  22   a  and the downstream exhaust chamber  32 , or may be longer than the distance between the ignition portion  22   a  and the downstream exhaust chamber  32 . 
     For example, in the axial direction of the flame stabilizer  16 , the ignition portion  22   a  may be arranged midway between the upstream exhaust chamber  31  and the downstream exhaust chamber  32 . In this case, the upstream exhaust chamber  31  and the downstream exhaust chamber  32  may be partitioned by two or more partition walls. In the configuration that partitions with one partition wall, the ignition portion  22   a  may be arranged inside the flame stabilizer  16  through the partition wall. With this configuration, the distance between the ignition portion  22   a  and the upstream exhaust chamber  31  is set to be equal to the distance between the ignition portion  22   a  and the downstream exhaust chamber  32  or to be longer than the distance between the ignition portion  22   a  and the downstream exhaust chamber  32 . 
     For example, the upstream exhaust chamber  31  may be defined by a partition wall and another wall different from the partition wall and arranged closer to the ejection port  16 A than the downstream exhaust chamber  32 . In this case, piping that connects the downstream exhaust chamber  32  and the ejection port  16 A may be modified as long as it is configured to be separately provided outside of the cover so that the exhaust gas of the downstream exhaust chamber  32  travels outside the cover and flows to the ejection port  16 A. 
     For example, the partition wall may extend in the direction that crosses the circumferential direction of the flame stabilizer  16 , and partition the upstream exhaust chamber  31  off from the downstream exhaust chamber  32  in the direction that crosses the circumferential direction of the flame stabilizer  16 . With this configuration, in the radial direction of the flame stabilizer  16 , the upstream exhaust chamber  31  and the downstream exhaust chamber  32  are arranged outside of the ignition portion  22   a . For this reason, the distance between the ignition portion  22   a  and the upstream exhaust chamber  31  is equal to the distance between the ignition portion  22   a  and the downstream exhaust chamber  32 , or longer than the distance between the ignition portion  22   a  and the downstream exhaust chamber  32 . 
     In other words, the partition portion may be modified as long as it is configured to partition the gap between the outer circumferential face of the flame stabilizer and the inner circumferential face of the cover into the upstream exhaust chamber  31  connected to the exhaust pipe and the downstream exhaust chamber  32  connected to the ejection port. 
     The flow path cross-sectional area of the exhaust pipe  11  may be less than or equal to the flow path cross-sectional area of the upstream exhaust chamber  31 . 
     The configuration for generating a swirling flow in the upstream exhaust chamber  31  is not limited to the exhaust pipe  11  that is offset from the upstream cover  13 , but may be formed, e.g., by arranging a guide plate for guiding the exhaust gas flowing into the upstream exhaust chamber  31  in the upstream exhaust chamber  31 . According to the first and second embodiments, the upstream exhaust chamber  31  is a continuous annular space. However, another configuration for generating a swirling flow in the upstream exhaust chamber  31  may be employed, e.g., by forming the upstream exhaust chamber  31  with a discontinuous space by a stopper arranged near the portion that connects the upstream cover  13  and the exhaust pipe  11 . 
     In the upstream exhaust chamber  31 , for example, the exhaust pipe  11  may extend in the radial direction of the outer surface of the upstream cover  13  so that the exhaust gas flowing from the exhaust pipe  11  is divided by the flame stabilizer  16  to form two flows. In addition, a plurality of exhaust pipes  11  may be connected to the upstream exhaust chamber  31  so that the exhaust gas flowing from the exhaust pipes  11  flows in different directions. In other words, this may be modified as long as it is configured that the exhaust gas of the exhaust pipes  11  passes through the upstream exhaust chamber  31 , the communication holes  35 , and the downstream exhaust chamber  32  in order. 
     The communication holes  35  may be omitted, and the partition portion may be configured such that the partition wall  33  is separated from the inner surface of the upstream cover  13 . The communication holes  35  may be omitted, and the partition portion may be configured such that the partition wall  33  is separated from the circumference wall of the flame stabilizer  16 . The partition portion may be configured to include two or more partition walls  33  configured as above. The plurality of communication holes  35  may be omitted from the partition wall  33 , and the upstream exhaust chamber  31  and the downstream exhaust chamber  32 , which are partitioned by the partition wall  33 , may be connected by, e.g., other piping arranged outside of the upstream cover  13 . 
     Not limited to piping for exhaust gas from the engine, the exhaust pipe  11  may be piping through which the exhaust gas that has passed through the DPF  12  flows. 
     The flame stabilizer  16  may have a tubular shape that has a constant diameter over the entire flame stabilizer in the axial direction. In other words, the flame stabilizer  16  may be modified as long as it is configured to have a tubular shape with the ejection port  16 A for ejecting combustion gas. 
     The fuel injected from the fuel injection valve  21  may be supplied from a common rail, not a fuel pump. A fuel pump that supplies fuel only to the fuel injection valve  21  may be included. 
     In the first embodiment, for example, the fuel injection valve  21  may be configured to supply fuel that is vaporized in advance to the combustion area  20 . 
     In the second embodiment, the fuel supply unit  58  may inject fuel that is not vaporized to the first mixing chamber  71 . 
     Not limited to a spark plug, a glow plug, a laser spark device, or a plasma spark device may be used to ignite air-fuel mixture. One of those or two or more of those may be used to ignite the air-fuel mixture. 
     Not limited to the intake air flowing through the intake pipe  25 , air for combustion may be air flowing through piping connected to the air tank of a brake or air supplied by a blower for the burner for an exhaust purification device. 
     The engine with the burner for an exhaust purification device may be a gasoline engine. 
     The exhaust gas with the temperature raised by the burner for an exhaust purification device is used for raising the temperature of a catalyst, not limited to a regeneration process of the DPF  12 . 
     DESCRIPTION OF THE REFERENCE NUMERALS 
     
         
         
           
             F: flame, T: ambient temperature, T 1 : ignitable temperature, t, t 1 , t 2 : elapsed time,  10 : exhaust purification device,  11 : exhaust pipe,  12 : diesel particulate filter,  13 : upstream cover,  14 : downstream cover,  15 : burner for an exhaust purification device,  16 : flame stabilizer,  16 A: ejection port,  17 : basal wall,  18 : small diameter portion,  19 : large diameter portion,  20 : combustion area,  21 : fuel injection valve,  22 : spark plug,  22   a : ignition portion,  23 : ignition point,  25 : intake pipe,  26 : air supply pipe,  27 : air valve,  31 : upstream exhaust chamber,  32 : downstream exhaust chamber,  33 : partition wall,  34 : opening,  35 : communication hole,  50 : burner for an exhaust purification device,  51 : outer tube,  52 : introduction flow path,  53 : closing wall,  54 : guide plate,  55 : first introduction port,  56 : second introduction port,  57 : raised piece,  58 : fuel supply unit,  60 : coupling portion,  61 : flange,  62 : insertion portion,  63 : radially-narrowed portion,  64 : first inner tube,  65 : second inner tube,  66 : closing wall,  67 : support plate,  68 : communication passage,  69 : wire mesh,  70 : premixing chamber,  71 : first mixing chamber,  72 : second mixing chamber,  73 : third mixing chamber,  74 : fourth mixing chamber, and  75 : fifth mixing chamber.