BURNER

A burner includes a partition wall that partitions a mixing chamber, which generates an air-fuel mixture, and a combustion chamber, which burns the air-fuel mixture. The partition wall includes a plurality of communication passages that communicate the mixing chamber with the combustion chamber. Further, a heating unit that heats the partition wall is attached to the partition wall. Such a structure heats the partition wall and a mesh with the heating unit and burns particulate matter deposited on the partition wall and the mesh.

TECHNICAL FIELD

The technology of the present disclosure relates to a burner including a partition wall that partitions a mixing chamber and a combustion chamber.

BACKGROUND ART

In the prior art, an exhaust gas passage for a diesel engine includes an exhaust purifying device that purifies the exhaust gas. The exhaust gas purifying device includes a diesel particulate filter (DPF) that removes, for example, particulate matter (PM) from the exhaust gas. To sustain the particulate matter capturing performance, the DPF undergoes a regeneration process that burns particulate matter captured in the DPF.

The regeneration process is performed by activating a burner located in front of the DPF. During the regeneration process, the burner supplies the exhaust gas passage with combustion gas that is generated in a combustion chamber of the burner. The exhaust gas, which is heated by the combustion gas, flows through the DPF and burns the particulate matter captured in the DPF (refer to, for example, patent document 1).

A premixing type burner is known as such a burner that reduces the unburned fuel in the combustion gas by supplying the mixture of air and fuel to the combustion chamber instead of separately supplying air and fuel to the combustion chamber. In the premixing type burner, the premixing chamber is divided from the combustion chamber with a partition wall. The air-fuel mixture generated in the premixing chamber flows into the combustion chamber through communication chambers formed by the partition wall.

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF THE INVENTION

Problems that are to be Solved by the Invention

When the burner is deactivated, some of the exhaust gas flowing through the exhaust gas passage flows into the combustion chamber. Thus, the particulate matter in the exhaust gas deposits on the partition wall. This changes the distribution and flow rate of the mixture in the combustion chamber in the next combustion and may consequently lower the ignition performance of the air-fuel mixture in the combustion chamber. This problem occurs not only when the particulate matter in the exhaust gas deposits on the partition wall but also when the particulate matter included in the combustion chamber deposits on the partition wall.

It is an object of the technology of the present disclosure to provide a burner that limits degradation in the ignitability of the air-fuel mixture.

Means for Solving the Problem

One aspect of the present disclosure is a burner including a partition wall with which a mixing chamber is divided from a combustion chamber. The mixing chamber generates an air-fuel mixture, and the combustion chamber burns the air-fuel mixture. A plurality of communication passages are formed by the partition wall to communicate the mixing chamber with the combustion chamber, and a heating unit heats the partition wall.

In the burner according to the one aspect of the present disclosure, the partition wall is heated by the heating unit. Thus, in comparison to a structure that does not heat the partition wall, deposits are more easily removed from the partition wall. This limits degradation in the ignitability of the air-fuel mixture caused by deposits on the partition wall.

A further aspect of the present disclosure is a burner provided with a combustion tube including a distal end defining an injection port that injects combustion gas, which is the burned air-fuel mixture. A first inner tube extends through the combustion tube toward the injection port. The air-fuel mixture flows into the first inner tube from a side opposite to the injection port. A second inner tube is arranged in the combustion tube and fitted into the first inner tube. The second inner tube includes a closed opening located toward the injection port. A connection wall is connected to an inner surface of the combustion tube and an outer surface of the first inner tube. The connection wall closes a gap between the combustion tube and the first inner tube. The partition wall is annular and connected to the inner surface of the combustion tube and an outer surface of the second inner tube. An ignition portion is located closer to the injection port than the partition wall to ignite the air-fuel mixture.

The burner of the present disclosure divides the interior of the combustion tube into a mixing chamber and a combustion chamber with the partition wall and a second tube having a closed opening located at the side of the injection port.

EMBODIMENTS OF THE INVENTION

First Embodiment

A first embodiment of a burner will now be described with reference toFIGS. 1 to 5. The entire structure of a diesel engine including the burner will first be described. Here, a passage for air, which is drawn into the diesel engine, and a passage for exhaust gas, which is discharged from the diesel engine, will mainly be described.

As shown inFIG. 1, a diesel engine10is provided with a cylinder block11including six in-line cylinders11a. Each cylinder11ais connected to an intake manifold12, which supplies each cylinder11awith intake air, and an exhaust manifold16, into which the exhaust gas from each cylinder11aflows.

An air cleaner14is coupled to an upstream end of an intake pipe13, which is a passage for the intake air and which is coupled to the intake manifold12. A compressor15of a turbo charger TC is arranged in the intake pipe13.

An EGR pipe17and an exhaust pipe18are connected to the exhaust manifold16. The exhaust pipe18is an element constituting an exhaust gas passage. When the intake pipe13and the exhaust manifold16are connected, exhaust gas flows into the intake pipe13through the EGR pipe17. A turbine19, which is coupled with the compressor15, is connected to the upstream side of the exhaust pipe18.

An exhaust gas purifying device20, which purifies the exhaust gas, is arranged at the downstream side of the exhaust pipe18. The exhaust gas purifying device20includes a diesel particulate filter21(hereafter, referred to as the DPF21) that captures particulate matter in the exhaust gas. The DPF21has a honeycomb structure formed from, for example, porous silicon carbide and captures particulate matter in the exhaust gas, with the inner wall surfaces of columnar bodies of the honeycomb structure. A burner40is arranged upstream of the DPF21to perform a regeneration process on the DPF21by heating the exhaust gas flowing into the DPF21.

An air supplying pipe25, which supplies the burner40with air, is connected to the intake pipe13at the downstream side of the compressor15. An air valve27is arranged in the air supplying pipe25. When the air valve27is open, the burner40is supplied with some of the intake air in the intake pipe13as combustion air.

Various types of sensors are fixed to the engine10to obtain information related to the operation conditions of the engine10. For example, an upstream exhaust gas flow rate sensor31, an upstream exhaust gas pressure sensor32, and an upstream exhaust gas temperature sensor33are fixed to the exhaust pipe18at the upstream side of the DPF21. The upstream exhaust gas flow rate sensor31detects the upstream exhaust gas flow rate Qep1, which is the mass flow rate of the exhaust gas flowing through the upstream side of the DPF21. The upstream exhaust gas pressure sensor32detects the upstream exhaust gas pressure Pep1, which is the pressure of the exhaust gas flowing through the upstream side of the DPF21. The upstream exhaust gas temperature sensor33detects the upstream exhaust pressure temperature Tep1, which is the temperature of the exhaust gas flowing through the upstream side of the DPF21.

A DPF temperature sensor34is fixed to the DPF21to detect the DPF temperature Td, which is the temperature of the DPF21. A downstream exhaust gas pressure sensor35is fixed to the exhaust pipe18at the downstream side of the DPF21to detect the downstream exhaust gas pressure Pep2, which is the pressure of the exhaust gas having passed through the exhaust gas purifying device20.

An intake air amount sensor36is fixed to the intake pipe13at the upstream side of the compressor15to detect the intake air amount Qa, which is the mass flow rate of the intake air flowing through the intake pipe13. An air flow rate sensor37, which detects the air flow rate Qad that is the mass flow rate of the combustion air flowing through the air supplying pipe25, and an air temperature sensor38, which detects the air temperature Tad that is the temperature of the air for fuel flowing through the air supplying passage, are fixed to the air supplying pipe25at the downstream side of the air valve27.

The structure of the burner40will now be described in further detail with reference toFIG. 2.

As shown inFIG. 2, the burner40has a double-tube structure including a cylindrical first tube41(hereafter, simply referred to as the tube41) and a second tube42(hereafter, simply referred to as the tube42), which has a larger inner diameter than the tube41. The basal ends of the tubes41and42are fixed to a base plate43, which closes the basal ends that are open. An annular closing plate44is fixed to the distal ends of the tubes41and42to close the gap between the tubes41and42. A generally annular injection plate45is coupled to the closing plate44, and an injection port46extends through the central portion of the injection plate45.

A partition wall49is coupled to the tube41to partition the interior of the tube41into a premixing chamber47and a combustion chamber48. The partition wall49is a perforated circular plate, and the outer rim49cof the partition wall49is joined with the inner circumferential surface of the tube41. Communication passages50, which communicate the premixing chamber47with the combustion chamber48, extend through the partition wall49in the thicknesswise direction of the partition wall49. The partition wall49includes a metal mesh51, which covers the opening of the each communication passage50, on the surface49afacing the combustion chamber48. The mesh51limits backfiring from the combustion chamber48to the premixing chamber47.

The air supplying pipe25is connected to the outer circumferential surface of the tube42at a position located toward the distal end from the partition wall49. The combustion air from the air supplying pipe25enters an air intake chamber52, which is the gap between the tube41and the tube42. First intake holes53are formed at the circumferential wall of the tube41entirely in the circumferential direction of the tube41at positions located toward the basal end from the partition wall49. The first intake holes53extend through the circumferential wall of the tube41to communicate the air intake chamber52with the premixing chamber47. Second intake holes54are formed at the circumferential wall of the tube41entirely in the circumferential direction of the tube41at positions located toward the distal end from the partition wall49. The second intake holes54extend through the circumferential wall of the tube41to communicate the air intake chamber52with the combustion chamber48. Thus, when the air valve27is open, some of the intake air flowing through the intake pipe13is supplied to the premixing chamber47through the air supplying pipe25, the air intake chamber52, and the first intake holes53, and some of the intake air is supplied to the combustion chamber48through the air supplying pipe25, the air intake chamber52, and the second intake holes54.

A fuel supplying unit55delivers fuel to an injection nozzle56, which is fixed to the central portion of the base plate43. The injection port of the injection nozzle56is arranged in the premixing chamber47. The fuel supplying unit55includes a fuel pipe, a fuel valve, and a heater (not shown). The fuel supplying unit55vaporizes the fuel, which flows when the fuel valve opens, with the heater and delivers the vaporized fuel to the injection nozzle56. The fuel delivered to the injection nozzle56is injected into the premixing chamber47from an injection port of the injection nozzle56. In the premixing chamber47, the fuel injected from the injection nozzle56is mixed with the combustion air drawn through the first intake holes53to generate an air-fuel mixture.

An ignition portion58of an ignition plug57is arranged in the combustion chamber48at a position located toward the partition wall49from the location where the second intake holes54are formed. The air-fuel mixture flows through the communication passage50of the partition wall49into the combustion chamber48, and the ignition portion58ignites the air-fuel mixture. This produces a flame that burns the air-fuel mixture in the combustion chamber48and generates combustion gas, which is the burned air-fuel mixture. The generated combustion gas flows into the exhaust pipe18through the injection port46.

A heating unit59is fixed to the partition wall49on a surface49bfacing away from the injection port46by a fastener (not shown). The heating unit59is a wire resistance heating element that is electrically insulated from the partition wall49and usable at a temperature that can burn the particulate matter in the exhaust gas, for example, at a temperature higher than approximately 600° C. The heating unit59includes two ends, each connected to a basal end of an electric wire60that supplies power to the heating unit59(refer toFIG. 3). The electric wires60, which are electrically insulated from the tube41and the base plate43by a coating material, extend toward the base plate43in the premixing chamber47.

A terminal base61is fixed to the base plate43. The terminal base61is inserted into a wire passage67, which extends through the base plate43. A seal (not shown) seals the gap between the terminal base61and the wire passage67. The terminal base61includes an interior terminal63, which is arranged inside the premixing chamber47, and an exterior terminal64, which is arranged outside the premixing chamber47. The interior terminal63of the terminal base61is connected to a connection terminal60A arranged on the distal end of the electric wire60, and the exterior terminal64of the terminal base61is connected to an electric wire65, which is further connected to a power supply device66. The terminal base61and the electric wire65are provided for each of the electric wires60connected to the two ends of the heating unit59.

FIG. 3is a front view showing the structure of the partition wall49in the first embodiment from the premixing chamber47. InFIG. 3, the ignition plug57and the ignition portion58, which are indicated by the double-dashed lines inFIG. 3, show where the ignition plug57and the ignition portion58are located as viewed from the front of the partition wall49.

As shown inFIG. 3, the heating unit59is attached to the surface49bto be symmetric at the left and right sides of an axis extending in the vertical direction when viewing the surface49bfacing the premixing chamber47from the front. Further, the heating unit59is attached to the surface49bavoiding the opening of the communication passages50. A region68in the partition wall49surrounded by the double-dashed lines defines a first portion located closer to the ignition portion58than the outer rim49cof the partition wall49as viewed from the front of the partition wall49. In the partition wall49, a region69between the outer rim49cof the partition wall49and the double-dashed lines defines a second portion located closer to the outer rim of the partition wall49than the ignition portion58as viewed from the front of the partition wall49.

The two ends of the heating unit59are located proximal to the outer rim49cof the partition wall49. One end of the heating unit59is located at the left lower side of the partition wall49in the region69, and the other end of the heating unit59is located at the right lower side of the partition wall49in the region69. The heating unit59extends from the two ends toward the center of the partition wall49. Further, the heating unit59is laid out in the region68so as to detour the center of the partition wall49and pass by a location overlapping the ignition portion58in the axial direction of the tube41(as viewed from the front of the partition wall49).

The electric structure of the burner40will now be described with reference toFIG. 4.

A burner controller70(hereafter, simply referred to as the controller70) controls the supply of fuel from the fuel supplying unit55, the ignition of the ignition plug57, the opening and closing of the air valve27, and the supply of power from the power supply device66to the heating unit59in the burner40. The controller70includes a CPU, a ROM, which stores various types of control programs and various types of data, and a RAM, which temporarily stores computation results of various types of computations and various types of data. The controller70executes various types of processes based on the control programs stored in the ROM. Here, a regeneration process will be described; a regeneration process which burns the particulate matter captured by the DPF21by heating the exhaust gas with the burner40.

Referring toFIG. 4, the controller70receives, in predetermined control cycles, a detection signal indicating the upstream exhaust gas flow rate Qep1from the upstream exhaust gas flow rate sensor31, a detection signal indicating the upstream exhaust gas pressure Pep1from the upstream exhaust gas pressure sensor32, and a detection signal indicating an upstream exhaust gas temperature Tep1from the upstream exhaust gas temperature sensor33. Further, the controller70receives, in predetermined control cycles, a detection signal indicating the DPF temperature Td from the DPF temperature sensor34, a detection signal indicating the downstream exhaust gas pressure Pep2from the downstream exhaust gas pressure sensor35, and a detection signal indicating an intake air amount Qa from the intake air amount sensor36. Moreover, the controller70receives, in predetermined cycles, a detection signal indicating the air flow rate Qad from the air flow rate sensor37and a detection signal indicating the air temperature Tad from the air temperature sensor38.

The controller70calculates the deposited amount M of particulate matter on the DPF21based on the pressure difference ΔP of the upstream exhaust gas pressure Pep1and the downstream exhaust gas pressure Pep2, and the upstream exhaust gas flow rate Qep1. The controller70starts the regeneration process of the DPF21under the condition that the deposited amount M becomes greater than a preset threshold α.

The controller70ends the regeneration process when the deposited amount M of the particulate matter calculated during the regeneration process becomes less than a preset threshold β (<α), which allows for determination that the particulate matter deposited on the DPF21has been sufficiently burned.

The controller70includes a power control unit71that outputs a start signal to the power supply device66to start the supply of power to the heating unit59. The power supply device66that receives the start signal supplies the heating unit59with predetermined power. When the deposited amount M of the particulate matter calculated during the regeneration process becomes less than the threshold β, the power control unit71outputs an end signal to the power supply device66to end the supply of power to the heating unit59. The power supply device66ends the supply of power to the heating unit59in response to the end signal.

The controller70includes a timer72that starts measuring the time when the start signal is output and resets the measurement value when the end signal is output. When the measurement C of the timer72exceeds a predetermined completion valve Cf, the controller70starts driving the fuel supplying unit55, the air valve27, and the ignition plug57. The completion value Cf is a value at which it may be assumed that the burning of the particulate matter deposited on the partition wall49and the mesh51has been completed.

The controller70includes a fuel supply control unit73that calculates the fuel injection amount Qf per unit time injected into the combustion chamber48from the fuel supplying unit55based on the upstream exhaust gas flow rate Qep1, the upstream exhaust gas temperature Tep1, the air flow rate Qad, the air temperature Tad, the DPF temperature Td, and the target temperature of the DPF21. The fuel injection amount Qf is the fuel amount needed to heat the exhaust gas flowing through the DPF21to heat the DPF21to the target temperature. The fuel supply control unit73outputs a control signal to the fuel supplying unit55so that the injection nozzle56injects the calculated fuel injection amount Qf. The fuel supplying unit55, which has received the control signal, drives a fuel injection valve and a heater in accordance with the control signal to inject fuel from the injection nozzle56.

The controller70includes an air valve control unit74that calculates an air supplying amount Qs that is the air amount corresponding to the fuel injection amount Qf. The air amount corresponding to the fuel injection amount Qf is the air amount per unit time needed to burn the fuel corresponding to the fuel injection amount Qf. The air valve control unit74outputs an open valve signal to the air valve27. The open valve signal is a control signal indicating the open degree of the air valve27needed to supply the burner40with air in correspondence with the intake air amount Qs, based on the intake air amount Qa, the air flow rate Qad, and the air temperature Tad. The air valve27, which has received the open valve signal, is controlled at an open angle corresponding to the open valve signal.

Further, if the deposited amount M of the particulate matter calculated when the regeneration process is performed becomes less than the threshold1, the air valve control unit74outputs a close valve signal, which is a control signal that closes the air valve27. This blocks the flow of the intake air in the air supplying pipe25from the intake pipe13.

The controller70includes an ignition plug control unit75that provides the ignition plug57with a control signal that drives the ignition plug57. The ignition plug57, which has received the control signal, generates a spark in the proximity of the ignition portion58.

The procedures for processing a regeneration process will now be described with reference toFIG. 5. As described above, the controller70starts the regeneration process under the condition that the deposited amount M is greater than the threshold α.

Referring toFIG. 5, in step S11, the controller70starts the regeneration process under the condition that the deposited amount M is greater than the threshold α.

As shown inFIG. 5, in step S11, the controller70starts heating the partition wall49by outputting a start signal to the power supply device66and supplying power to the heating unit59. Further, the controller70starts measuring the time with the timer72. In following step S12, the controller70repeatedly determines whether or not the measurement C of the timer72has exceeded the completion value Cf.

When the measurement C of the timer72has exceeded the completion value Cf (step S12: YES), that is, when assumed that the particulate matter deposited on the partition wall49and the mesh51has been burned, the controller70proceeds to following step S13.

In step S13, the controller70obtains, from the sensors, the upstream exhaust gas flow rate Qep1, the upstream exhaust gas temperature Tep1, the air flow rate Qad, the air temperature Tad, the intake air amount Qa, and the DPF temperature Td. In following step S14, the controller70calculates fuel injection amount Qf and the air supply amount Qs corresponding to the fuel injection amount Qf.

In following step S15, the controller70outputs a control signal to the fuel supplying unit55to drive the fuel supplying unit55and inject the amount of fuel corresponding to the fuel injection amount Qf into the premixing chamber47. Further, based on the intake air amount Qa and the air supply amount Qs, the controller70outputs a control signal to the air valve27and drives the air valve27to draw the amount of combustion air corresponding to the air supply amount Qs into the air intake chamber52. The controller70also outputs a control signal to the ignition plug57to drive the ignition plug57.

This ignites the air-fuel mixture, which is generated by the premixing chamber47, in the combustion chamber48with the ignition plug57. The combustion gas generated in the combustion chamber48is mixed with the exhaust gas flowing through the exhaust pipe18to heat the exhaust gas that flows to the DPF21. The heated exhaust gas flows into the DPF21and burns the particulate matter deposited on the DPF21.

In following step S16, the controller70newly obtains the upstream exhaust gas pressure Pep1from the upstream exhaust gas pressure sensor32, the downstream exhaust gas pressure Pep2from the downstream exhaust gas pressure sensor35, and the upstream exhaust gas flow rate Qep1from the upstream exhaust gas flow rate sensor31.

In following step S17, the controller70computes the pressure difference ΔP of the upstream exhaust gas pressure Pep1and the downstream exhaust gas pressure Pep2and calculates the deposited amount M for the DPF21based on the pressure difference ΔP and the upstream exhaust gas flow rate Qep1. Then, in following step S18, the controller70determines whether or not the deposited amount M is less than or equal to the threshold β.

When the deposited amount M exceeds the threshold β (step S18: NO), the controller70repeats the processing of step S13to step S18.

When the deposited amount M is less than or equal to the threshold β (step S18: YES), in following step S19, the controller70outputs an end signal to the power supply device66to stop the supply of power to the heating unit59. Further, the controller70resets the measurement C of the timer72. The controller70also outputs an end signal to the fuel supplying unit55, a close valve signal to the air valve27, and a suspension signal to the ignition plug57. The controller70then ends the regeneration process.

The operation of the burner40will now be described.

In the burner40, the heating unit59heats the partition wall49and the mesh51to temperatures at which particulate matter can be burned to burn the particulate matter deposited on the partition wall49and the mesh51. This opens the communication passages50that were at least partially closed by particulate matter. Thus, the air-fuel mixture that flows into the combustion chamber48from the premixing chamber47is evenly distributed and the flow rate of the air-fuel mixture is also lowered. As a result, the air-fuel mixture is supplied with a high probability to the vicinity of the ignition portion58, and the occurrence of misfires caused by the flow rate of the air-fuel mixture is lowered. This makes it harder for the particulate matter deposited on the partition wall49to have an influence on the air-fuel mixture, and limits degradation in the ignitability of the air-fuel mixture.

Further, as shown inFIG. 3, the heating unit59is in contact with the region68, which is the first portion, and the region69, which is the second portion, and passes by a location overlapped with the ignition portion58in the axial direction of the tube41(when viewing the partition wall49from the front). Thus, for example, in comparison to when the heating unit59is in contact with only the region69, in the partition wall49, the temperature of the region68that is proximal to the ignition portion58is quickly heated. As a result, the particulate matter deposited near the ignition portion58is easily burned. This supplies air-fuel mixture to the proximity of the ignition portion58with a high probability. Thus, degradation in the ignitability of the air-fuel mixture is efficiently limited.

The heating unit59is in contact with both of the region68, which is the first portion, and the region69, which is the second portion. Thus, in comparison to when the heating unit59is in contact with only the region68or only the region69, the temperature is increased entirely and quickly in the partition wall49. As a result, particulate matter is burned entirely on the partition wall49. This further limits decreases in the ignitability of the air-fuel mixture.

The heating unit59is attached to the partition wall49on the surface49bat the side of the premixing chamber47. Thus, in comparison to when the heating unit59is attached to the surface′49aat the side of the combustion chamber48, it is less important for the heating unit59to have a high heat resistance, and it is less important for the electric wires60to have a high heat resistance. The electric wires60are joined with the heating unit59. Further, in comparison with when the heating unit59is incorporated in the partition wall49, it is not so hard to manufacture the partition wall49.

The heating unit59performs heating immediately before the ignition by the ignition portion58. In other words, the ignition portion58performs an ignition when the temperature of the partition wall49is raised by the heating unit59. As a result, in comparison to when the ignition by the ignition portion58is performed before the temperature of the partition wall49is increased, the ignition portion58performs an ignition when the deposited amount of the particulate matter is small on the partition wall49and the mesh51. Further, the air-fuel mixture passing through the communication passages50is heated with the partition wall49. This improves the ignitability of the air-fuel mixture.

Further, the heating unit59continues to heat the partition wall49until the deposited amount M of particulate matter on the DPF21becomes less than or equal to the threshold β. That is, the partition wall49is maintained at a temperature that can burn the particulate matter after the ignition by the ignition portion58and during a period in which the air-fuel mixture is burned in the combustion chamber48. Thus, the air-fuel mixture flowing into the combustion chamber48is heated with the partition wall49when passing through the communication passages50. As a result, in addition to the ignitability of the air-fuel mixture, the combustion properties of the air fuel mixture are improved.

As described above, the burner40of the first embodiment has the advantages described below.

(1) The particulate matter deposited on the partition wall49and the mesh51is burned. This lowers the influence which the particulate matter captured by the partition wall49has on the ignition of the air-fuel mixture, and improves the ignitability of the air-fuel mixture.

(2) The heating unit59is in contact with the region68, which is the first portion. Thus, the heating unit59directly heats the region68, and the particulate matter deposited at a location proximal to the ignition portion58is easily burned. This efficiently limits degradation in the ignitability of the air-fuel mixture.

(3) The heating unit59is arranged in the region68and the region69, which is the second portion. Thus, the temperature is increased entirely and quickly in the partition wall49. As a result, in comparison to when only one of the region68and the region69is directly heated, degradation in the ignitability of the air-fuel mixture is further limited.

(4) The heating unit59is attached to the surface49bat the side of the premixing chamber47. Thus, it is less important for the heating unit59and the electric wires60joined with the heating unit59to have a high heat resistance. Further, it is not so hard to manufacture the partition wall49.

(5) The heating unit59performs heating immediately before ignition by the ignition portion58. This ignites the air-fuel mixture when the deposited amount of particulate matter is small on the partition wall49and the mesh51, and heats the air-fuel mixture passing through the communication passages50with the partition wall49. As a result, the ignitability of the air-fuel mixture are improved.

(6) The heating unit59continues to heat the partition wall49until the deposited amount M of the particulate matter on the DPF21becomes less than or equal to the threshold β. As a result, the ignitability of the air-fuel mixture are improved and the combustion properties of the air-fuel mixture are improved in comparison to when the heating unit59suspends heating before an ignition by the ignition portion58, that is, before the air-fuel mixture is burned in the combustion chamber48.

Second Embodiment

A second embodiment of a burner will now be described with reference toFIGS. 6 and 7. A burner76of the second embodiment differs from the burner40of the first embodiment in the structure of the premixing chamber. Portions differing from the first embodiment will be described in detail for the second embodiment, and portions functioning in the same manner as the first embodiment are given the same reference numbers and will not be described in detail.

As shown inFIG. 6, in the burner76, the first tube41corresponds to a combustion tube in the claims. An annular connection wall77, as viewed from above in the axial direction of the tube41, connects a cylindrical third tube78(hereafter, simply referred to as the tube78) to the inner circumferential surface of the tube41. The tube78corresponds to a first inner tube in the claims. The rim of the connection wall77is fixed to the tube41at a position located toward the base plate43, and the connection wall77closes the gap between the inner circumferential surface of the tube41and the outer circumferential surface of the tube78. The tube78is connected to the connection wall77when fitted into an inner fitting portion79of the connection wall77. Further, the tube78has an open end located toward the injection port46.

In the tube41, at a portion closer to the base plate43than the portion connecting the tube41and the connection wall77, first intake holes53are formed at predetermined intervals in the circumferential direction. The first intake holes53draw combustion air from the air intake chamber52into a first mixing chamber91(hereafter, simply referred to as the mixing chamber91), which is the area surrounded by the base plate43, the tube41, and the connection wall77. The first intake holes53are formed by cutting and bending portions of the circumferential wall of the tube41toward the inner side. The tube41includes bent pieces80formed by the cut and bent portions. The bent pieces80guide the combustion air so that the air flowing into the mixing chamber91from the air intake chamber52swirls in the mixing chamber91.

The tube78includes a second mixing chamber92, which is an area surrounded by the circumferential wall of the tube78. A portion of the tube78is fitted into a cylindrical fourth tube81(hereafter, simply referred to as the tube81). The tube81corresponds to a second inner tube in the claims. The tube81projects toward the injection port46from the tube78. A closing plate82closes the open end of the projecting portion (distal end of tube81). The end of the tube81at the side opposite to the injection port46(basal end of tube81) is located closer to the injection port46than the portion connecting the tube41and the connection wall77. An annular partition wall49fixes the basal end to the tube41.

The partition wall49of the second embodiment includes an inner rim entirely connected to the outer circumferential surface of the tube81. The outer rim of the partition wall49is entirely connected to the inner circumferential surface of the tube41. The partition wall49includes communication passages83, which are arranged along a circle having a small diameter, and communication passages84, which are arranged along a circle having a large diameter. Thus, the centers of the openings of the communication passages83and84are arranged along concentric circles having different diameters (refer toFIG. 7).

A third mixing chamber93(hereafter, simply referred to as the mixing chamber93) is located toward the injection port46from the tube78. The mixing chamber93is an area surrounded by the tube81and the closing plate82and in communication with the mixing chamber92. The gap between the tube78and the tube81defines a fourth mixing chamber94(hereafter, simply referred to as the mixing chamber94), which is in communication with the mixing chamber93. The area surrounded by the tube41, the partition wall49, and the connection wall77at the side of the mixing chamber94facing away from the injection port46defines a fifth mixing chamber95(hereafter, simply referred to as the mixing chamber95), which is in communication with the mixing chamber94.

Accordingly, in the burner76, the mixing chambers91,92,93,94, and95form a premixing chamber90. The gap between the tube41and the tube81and the area surrounded by the tube41located toward the injection port46from the closing plate82defines a combustion chamber96. The premixing chamber90is divided from the combustion chamber96with the partition wall49.

A heating unit59is fixed to the partition wall49on the surface49bfacing away from the injection port46by a fastener (not shown). The heating unit59includes two ends, each connected to a basal end of an electric wire60that supplies power to the heating unit59. The electric wires60are electrically insulated from the tube41by a coating material. A connection terminal60A, which is arranged on the distal end of each of the electric wires60, is connected to an interior terminal of a terminal base86, which is coupled to the circumferential wall of the tube41. The terminal base86includes an exterior terminal that is located in the air intake chamber52and connected to an electric wire87. The electric wire87is electrically insulated from the tube41and the base plate43by a coating material.

The electric wires87each extend through the air intake chamber52toward the base plate43and connect to an interior terminal of a terminal base88fixed to the base plate43. The exterior terminal of the terminal base88is connected to an electric wire89, and the electric wire89is connected to the power supply device66. Each of the electric wires60joined with the two ends of the heating unit59is provided with the terminal bases86and88and the electric wires87and89.

FIG. 7is a front view showing the structure of the partition wall49in the second embodiment as viewed from the mixing chamber95. As shown inFIG. 7, the heating unit59is attached to the surface49bto be symmetric at the left and right sides of an axis extending in the vertical direction when viewing the surface49bfrom the mixing chamber95. The two ends of the heating unit59are located at positions proximal to the outer rim49cof the partition wall49. The heating unit59extends from the two ends toward the center of the partition wall49and then between the communication passages83and the communication passages84in the circumferential direction of the partition wall49. The heating unit59passes by a location overlapped with the ignition portion58as viewed from the front of the partition wall49in the region68.

As described above, the burner76of the second embodiment has the same advantages as the burner40of the first embodiment.

The burners of the first and second embodiments may be modified as described below.

The heating by the heating unit59may be suspended at any timing as long as the measurement C of the timer72has reached the completion value Cf. For example, the heating may be suspended at the point of time the measurement C of the timer72reaches the completion value Cf or at the point of time the measurement C of the timer72reaches a predetermined measurement value that is greater than the completion value Cf.

The heating by the heating unit59does not have to be performed immediately before an ignition by the ignition portion58and may be performed cyclically regardless of the timing at which the ignition portion58performs an ignition. Even in such a structure, compared to a burner in which the heating unit59does not perform heating, the probability is increased in that the ignition portion58performs an ignition when the deposited amount of particulate matter on the partition wall49is small.

The heating unit59may be attached to the surface49aof the partition wall49and arranged in the combustion chamber. Alternatively, the heating unit59may be incorporated in the partition wall49or be spaced apart from the partition wall49. It is only necessary that the heating unit be located at a position where it can heat the partition wall49.

The heating unit59may be attached to the partition wall49with the mesh51located between the heating unit59and the partition wall49. Such a structure heats the mesh51more easily than the partition wall49and thus quickly burns the particulate matter deposited on the mesh51.

The mesh51may be omitted from the burners40and76.

The heating unit59may be in contact with the first portion and the second portion, only the first portion, or only the second portion. Further, the temperature of the first portion may be the same as the temperature of the second portion. Alternatively, the temperature of the first portion may be higher than the temperature of the second portion or the temperature of the first portion may be lower than the temperature of the second portion. It is only required that the partition wall49be heated.

For example, as shown inFIG. 8, when viewing the surface49bfacing the premixing chamber47from the front, the heating unit59may have a star-shaped polygonal shape extending along the entire circumference of the partition wall49and, in the vicinity of the ignition portion58, be overlapped with the ignition portion58as viewed from the front of the partition wall49. In such a structure, when the heating unit59performs heating, portions having a low temperature and portions having a high temperature are not locally formed in an easy manner. Thus, the partition wall49is heated while limiting variations in the temperature distribution. It is preferable that the heating unit59be shaped to be symmetric at the left and right sides of an axis extending in the vertical direction to heat the partition wall49while limiting variations in the temperature distribution.

A structure in which the heating unit59heats the partition wall49so that the temperature of the first portion is higher than the temperature of the second portion especially limits changes in the condition of the air-fuel mixture caused by deposits on the partition wall49at a portion relatively close to the ignition portion58. This efficiently limits degradation in the ignitability of the air-fuel mixture.

A plurality of heating units59may be attached to the partition wall49. For example, a heating unit59may be attached on each of the surface49aand the surface49bof the partition wall49. Alternatively, a plurality of heating units59may be attached to the surface49bof the partition wall49.

The heating unit is not limited to a linear heating element and may be a planar heating element as long as it may be attached to a partition wall without overlapping openings of communication passages. Further, a heating body only needs to be a heating element that may be used at a temperature that can burn the particulate matter in the exhaust gas, for example, 600° C. The heating body is not limited to a metal heating element like a resistance heating element and may be, for example, a non-metal heating element such as a silicon carbide heating element.

The wires for supplying power to the heating unit may be changed in accordance with the design conditions.

The burner controller70may be formed by a single electronic control unit or a plurality of electronic control units.

In addition to the regeneration process of the DPF21, the heating by the burners40and76may be applied to, for example, a catalyst heating process that heats a catalyst of an exhaust gas purifying device.

The engines to which the burners40and76are applied may be gasoline engines. In addition to engines, the burners40and76may be applied to, for example, heating appliances.

DESCRIPTION OF REFERENCE CHARACTERS