Light and dark burner

Abstract

To suppress the generation of resonance vibration having frequencies of 200 Hz to 250 Hz or more less without largely increasing the passage resistance of a lean air-fuel mixture of a rectification member 7, in a rich-lean burner which has a learn flame hole 2 in a fore-and-aft direction, and a rich flame hole 4 adjoining the learn flame hole with an air gap part 3 sandwiched therebetween at least at one side of the lean flame hole 2 in a lateral direction at an upper end part, and in which a throttle part 73 for dividing the learn flame hole 2 into a plurality of fore-and-aft portions by making a plurality of rectification plates 71, 72 adhere to a plurality of fore-and-aft points of the rectification member 7 having the plurality of rectification plates 71, 72 for partitioning the learn flame hole 2 into a plurality of regions in the lateral direction at upper parts of the rectification plates.SOLUTION: A second throttle part 74 for further dividing each portion of a learn flame hole which is divided by a throttle part 73 into a plurality of fore-and-aft points while adhering to a rectification plate 71 which adjoins in a lateral direction is arranged at a rectification plate 72 at least at the outermost side in the lateral direction. The second throttle part 74 is located above a lower end of the throttle part 73 at its lower end, and a vertical length is shorter than the throttle part 73.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a lean burner having, at its upper end, a lean flame port elongated in the front-to-rear direction for spraying a lean mixture with a fuel concentration leaner than the stoichiometric air-fuel ratio, and a rich flame port adjacent to at least one lateral side of the lean flame port across a gap of a predetermined width for spraying a rich mixture with a fuel concentration richer than the stoichiometric air-fuel ratio. [Background technology]

[0002] Conventionally, this type of thick / thin burner is equipped with a straightening member having a plurality of straightening plates that divide the thin flame port into a plurality of regions in the horizontal direction (see, for example, Patent Document 1). In addition, at a plurality of locations on the front and rear of the straightening member, there are provided throttle sections that bring the plurality of straightening plates into close contact with each other at the top of these straightening plates and divide the thin flame port into a plurality of front and rear sections.

[0003] In such a rich-lean burner, the rich mixture ejected from the rich flame port is combusted in the outer portion opposite the lean flame port by secondary air flowing outside the burner, and in the inner portion closer to the lean flame port, excess air in the lean mixture is supplied above the gap between the lean flame port and the rich-lean burner. If a uniform flame is formed over a wide area in the front-to-rear direction above the gap due to the combustion of a mixture with an excess air ratio of around 1.0, resonant vibrations with a frequency of around 200 Hz to 250 Hz are likely to occur.

[0004] Here, at the longitudinal position corresponding to the throttle portion, the supply of excess air in the lean mixture to the rich mixture is suppressed, and a flame caused by the combustion of a mixture with an air excess ratio of approximately 1.0 is not formed above the gap. Therefore, by increasing the number of throttle portions, the flame caused by the combustion of a mixture with an air excess ratio of approximately 1.0 that is formed above the gap is broken down, and the occurrence of resonant vibration with a frequency of approximately 200 Hz to 250 Hz can be suppressed. However, increasing the number of throttle portions increases the resistance to the passage of the lean mixture through the straightening member. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-286448 Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above, the present invention aims to provide a rich / lean burner that can suppress the occurrence of resonant vibrations with frequencies of approximately 200 Hz to 250 Hz without significantly increasing the resistance to the passage of lean mixtures through the straightening member. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides a lean-flame burner having, at its upper end, a lean flame port that is elongated in the front-to-rear direction and that sprays a lean mixture with a fuel concentration leaner than the stoichiometric air-fuel ratio, and a rich flame port that is adjacent to at least one side of the lean flame port in the horizontal direction, with a gap of a predetermined width between them, and that sprays a rich mixture with a fuel concentration richer than the stoichiometric air-fuel ratio; the burner is provided with a straightening member having a plurality of straightening plates that divide the lean flame port into a plurality of regions in the horizontal direction, and first throttling sections are provided at multiple locations in the front and rear of the straightening member, by bringing the plurality of straightening plates into close contact with each other at the top of these straightening plates, dividing the lean flame port into a plurality of front and rear sections; and the second throttling section is characterized in that the lower end of the second throttling section is located above the lower end of the first throttling section and has a shorter vertical length than the first throttling section.

[0008] According to the present invention, the straightening member is provided with a second throttle portion in addition to a first throttle portion, so that the flame formed above the gap due to the combustion of an air-fuel mixture with an excess air ratio of approximately 1.0 is more fragmented than in a configuration with only a first throttle portion, thereby suppressing the occurrence of resonant vibrations with a frequency of approximately 200 Hz to 250 Hz. Moreover, the second throttle portion has a lower end located above the lower end of the first throttle portion and is shorter in the vertical direction than the first throttle portion, so the resistance to the passage of a lean air-fuel mixture through the straightening member does not increase significantly. Note that, if a second throttle portion is provided on the horizontally outermost straightening vane adjacent to the gap, the above effect can be achieved to some extent even if the other straightening vanes do not have second throttle portions.

[0009] Furthermore, in the present invention, when the second throttle portions are provided on the plurality of straightening vanes, it is desirable that the second throttle portions provided on at least some of the plurality of straightening vanes have a width in the front-rear direction narrower than that of the first throttle portions, thereby further suppressing an increase in passage resistance due to the second throttle portions.

[0010] Furthermore, in the present invention, when second throttle portions are provided on a plurality of straightening plates, it is desirable that the upper ends of the second throttle portions provided on at least some of the plurality of straightening plates are located below the upper ends of the straightening plates. In this way, the lean air-fuel mixture flows at a low speed above the second throttle portions whose upper ends are located below the upper ends of the straightening plates, forming a short, stable flame and achieving a flame stabilization effect.

[0011] In addition, in the present invention, it is desirable that the positions of the second throttling portion provided on one of the two adjacent flow straightening vanes on the outer and inner sides in the lateral direction and the second throttling portion provided on the other flow straightening vane are offset in the vertical direction by a range shorter than the vertical length of the second throttling portion, so that the upper end of the second throttling portion provided on one flow straightening vane reaches the upper end of the flow straightening vane, but the upper end of the second throttling portion provided on the other flow straightening vane is located below the upper end of the flow straightening vane. This not only achieves the flame stabilization effect described above, but also makes it possible to narrow the front-to-rear width of the second throttling portion as described below, which helps to suppress an increase in passage resistance.

[0012] Furthermore, in the present invention, it is desirable to provide a plurality of inlet holes, spaced apart in the front-rear direction, for introducing a portion of the lean mixture into the gap, located below the lower end of the second throttle section in a portion of the laterally outermost straightening vane other than the first throttle section. This arrangement lowers the position at which the excess air in the lean mixture is supplied to the rich mixture, resulting in an excess air ratio of 1.0, due to the supply of the lean mixture from the gap. Therefore, combustion noise due to oscillatory combustion with a relatively low frequency of 60 Hz to 80 Hz, which occurs when this position is high, can be suppressed. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a perspective view of a concentration burner according to an embodiment of the present invention; [Figure 2] 1 is a perspective view of a burner body and a flow straightening member of a concentrated / light burner according to an embodiment of the present invention in a separated state; [Figure 3] FIG. [Figure 4] FIG. 4 is an enlarged cross-sectional view taken along line IV-IV in FIG. 3. [Figure 5] An enlarged cross-sectional view taken along line VV in Figure 3. [Figure 6] 6 is a cross-sectional side view taken along line VI-VI in FIG. 4. [Figure 7] FIG. 7 is a cross-sectional side view taken along line VII-VII in FIG. 4. DETAILED DESCRIPTION OF THE INVENTION

[0014] 1 to 4, reference numeral 1 denotes a rich-lean burner according to an embodiment of the present invention. This rich-lean burner 1 has, at its upper end, a lean flame port 2 elongated in the front-to-rear direction for ejecting a lean mixture whose fuel concentration is leaner than the stoichiometric air-fuel ratio, and a pair of rich flame ports 4, 4 adjacent to both sides of the lean flame port 2 in the lateral direction, sandwiching gaps 3, 3 of a predetermined width therebetween, for ejecting a rich mixture whose fuel concentration is richer than the stoichiometric air-fuel ratio.

[0015] The rich / lean burner 1 comprises, as burner components, a burner body 5 having a pair of side plates 51, 51 facing each other laterally, with the lean flame port 2 and gaps 3, 3 on both sides of it in the lateral direction defined between the upper ends of these side plates 51, 51, and a burner cap 6 having a pair of side plates 61, 61 covering the burner body 5 from both sides in the lateral direction, with rich flame ports 4, 4 defined between the upper ends of these side plates 61, 61 and the upper ends of both side plates 51, 51 of the burner body 5. The burner cap 6 also comprises a rectifying member 7 attached between the upper ends of the side plates 51, 51 of the burner body 5, and having a plurality of rectifying plates 71, 72 that divide the lean flame port 2 into a plurality of regions in the lateral direction.

[0016] The two side plates 51, 51 of the burner body 5 are formed by folding a single plate in a palm-to-palm state along a folding line that forms the lower edge of the burner body 5. The burner body 5 is also provided with a lean mixture pipe section 52, which is formed by pressing the two side plates 51, 51, and extends rearward from an inlet 52a that opens at the front end of the lower part of the burner body 5, and a lean passage section 53 that guides the lean mixture from the lean mixture pipe section 52 to the lean flame port 2. The opening area of the inlet 52a of the lean mixture pipe section 52 is relatively large. Therefore, a relatively large amount of primary air flows into the lean mixture pipe section 52 together with fuel gas from a lean gas nozzle (not shown) facing the inlet 52a, generating a lean mixture. The lean passage section 53 extends upward and forward from the rear end of the lean mixture pipe section 52.

[0017] Furthermore, a rich mixing tube section 54 formed by pressing both side plates 51, 51 is provided in the portion of the burner body 5 between the lean mixing tube section 52 and the lean passage section 53. The rich mixing tube section 54 extends a short distance rearward from an inlet 54a that opens at the front end of the burner body 5 and terminates therein. An outlet hole 54b is opened on the rear outer surface of the rich mixing tube section 54. The opening area of the inlet 54a of the rich mixing tube section 54 is relatively narrow. Therefore, a relatively small amount of primary air flows into the rich mixing tube section 54 together with fuel gas from a rich gas nozzle (not shown) facing the inlet 54a, and a rich mixture is generated.

[0018] The rich mixture flowing out from the outlet hole 54b of the rich mixture tube section 54 is guided to each rich flame port 4 through a rich passage section 62 defined between each side plate 51 of the burner body 5 and each side plate 61 of the burner cap 6. In addition, recesses 63 are formed at multiple locations on the front and rear of the upper part of each side plate 61 of the burner cap 6, dividing the rich flame port 4 into multiple (specifically, 12) sections on the front and rear.

[0019] The flow straightening member 7 has a pair of inner flow straightening plates 71, 71 on the inner side in the horizontal direction and a pair of outer flow straightening plates 72, 72 located on both outer sides in the horizontal direction. Furthermore, a longitudinal groove 55 is formed in the upper part of each side plate 51 of the burner body 5, which is in contact with the outer flow straightening plate 72, which is the outermost flow straightening plate in the horizontal direction of the flow straightening member 7. A gap 3 is defined between the part of the side plate 51 above this groove 55 and the outer flow straightening plate 72.

[0020] First throttle sections 73 are provided at multiple locations (specifically, three locations) in the front and rear of the rectifying member 7, which bring the multiple rectifying plates 71, 72 into close contact with each other at their upper parts, dividing the thin flame port 2 into multiple (specifically, four) front and rear sections. Each of the rectifying plates 71, 72 is also provided with a second throttle section 74 that is in close contact with the rectifying plate adjacent to each of the rectifying plates 71, 72 in the horizontal direction, and further divides each of the sections of the thin flame port 2 divided by the first throttle section 73 into multiple (specifically, three) front and rear sections. Specifically, as shown in Figure 5, the second constriction portions 74, 74 recessed inward in the horizontal direction and provided on a pair of inner straightening plates 71, 71 are in close contact with each other, dividing the area of the thin flame port 2 between the two inner straightening plates 71, 71 into front and rear portions, and the second constriction portion 74 recessed inward in the horizontal direction and provided on the outer straightening plate 72, which is the horizontally outermost straightening plate adjacent to the gap portion 3, is in close contact with the inner straightening plate 71, dividing the area of the thin flame port 2 between the inner straightening plate 71 and the outer straightening plate 72 into front and rear portions.

[0021] The front-rear direction positions of the first and second throttle portions 73, 74 of the straightening member 7 are the same as the front-rear direction positions of the recesses 63 of the side plates 61 of the burner cap 6. In addition, the recess 63 designated by the symbol #1 in Fig. 1, which is located at the same front-rear direction position as the first throttle portion 73, is larger than the other recesses 63. Furthermore, the burner cap 6 is provided with a bridge portion 64, which connects the both side plates 61, 61 of the burner cap 6 at their upper edges, at the same front-rear direction position as the first throttle portion 73.

[0022] 6 and 7 , the lower end of the second throttling portion 74 is located higher than the lower end of the first throttling portion 73, and the vertical length is shorter than that of the first throttling portion 73. The second throttling portion 74 provided on the outer flow vane 72 has the same front-to-rear width as the first throttling portion 73, but the front-to-rear width W1 of the second throttling portion 74 provided on the inner flow vane 71 is narrower than the front-to-rear width W2 of the first throttling portion 73. Note that the front-to-rear width of the second throttling portion 74 provided on the outer flow vane 72 may be narrower than the front-to-rear width of the first throttling portion 73, and the front-to-rear width of the second throttling portion 74 provided on the inner flow vane 71 may be equal to the front-to-rear width of the first throttling portion 73. Alternatively, the front-to-rear width of the second throttling portions 74 provided on both the inner and outer flow vanes 71, 72 may be narrower than the front-to-rear width of the first throttling portion 73. In short, the width in the front-rear direction of the second throttle portion 74 provided on at least some of the plurality of rectifying plates 71, 72 of the rectifying member 7 may be made narrower than the width in the front-rear direction of the first throttle portion 73.

[0023] By providing the second throttling portion 74 as described above, the flame formed above the gap 3 due to the combustion of an air-fuel mixture with an excess air ratio of approximately 1.0 is broken down into smaller flames than when the rectifier member 7 is provided with only the first throttling portion 73, thereby suppressing the occurrence of resonant vibrations with a frequency of approximately 200 Hz to 250 Hz. Moreover, since the lower end of the second throttling portion 74 is located higher than the lower end of the first throttling portion 73 as described above and its vertical length is shorter than that of the first throttling portion 73, the passage resistance of the lean air-fuel mixture through the rectifier member 7 does not increase significantly. Furthermore, by making the front-rear direction width of the second throttling portion 74 provided on at least some of the rectifier plates 71, 72 of the rectifier member 7 narrower than the front-rear direction width of the first throttling portion 73, the increase in passage resistance due to the second throttling portion 74 can be further suppressed.

[0024] It is also possible to reduce the passage resistance by shortening the vertical length or front-to-rear width of the first throttling portion 73. However, in order to rectify the flow of the lean mixture that flows into the front or rear of the lean flame port 2 and is tilted relatively greatly in the front-to-rear direction so that it flows upward, the vertical length of the first throttling portion 73 needs to be at least to a certain extent, and further, in order to prevent the bridge portion 64 from being burned by the flame, the front-to-rear width of the first throttling portion 73 located directly below the bridge portion 64 also needs to be at least to a certain extent. For this reason, it is not preferable to shorten the vertical length or front-to-rear width of the first throttling portion 73.

[0025] Furthermore, in this embodiment, the positions of the second throttling portion 74 provided on the inner flow rectifying plate 71 and the second throttling portion 74 provided on the outer flow rectifying plate 72 are offset in the vertical direction by a distance shorter than the vertical length of the second throttling portion 74. Specifically, the position of the second throttling portion 74 provided on the outer flow rectifying plate 72 is offset upward so that the upper end of this second throttling portion 74 reaches the upper end of the outer flow rectifying plate 72, and the position of the second throttling portion 74 provided on the inner flow rectifying plate 71 is offset downward so that the upper end of this second throttling portion 74 is located below the upper end of the inner flow rectifying plate 71.

[0026] Here, when the positions of the second throttling portion 74 provided on the inner flow plate 71 and the second throttling portion 74 provided on the outer flow plate 72 are not misaligned in the vertical direction, it is necessary to bring the second throttling portion 74 provided on the outer flow plate 72 into close contact with the second throttling portion 74 provided on the inner flow plate 71 in order to divide the area of the thin flame port 2 between the inner flow plate 71 and the outer flow plate 72 into front and rear. To do this, the front-rear width of the second throttling portion 74 provided on the inner flow plate 71 needs to be wide enough to accommodate the second throttling portion 74 provided on the outer flow plate 72. In contrast, according to this embodiment, the area of the thin flame port 2 between the inner flow plate 71 and the outer flow plate 72 can be divided into front and rear by bringing the upper part of the second throttling portion 74 provided on the outer flow plate 72, which is offset upward, into close contact with a part of the inner flow plate 71 above the upper end of the second throttling portion 74 provided on the inner flow plate 71, as shown in FIG. Therefore, it is not necessary to make it possible to insert the second throttling portion 74 provided on the outer flow plate 72 into the second throttling portion 74 provided on the inner flow plate 71. As a result, the front-to-rear width of the second throttling portion 74 provided on the inner flow plate 71 can be narrowed, which helps to suppress an increase in passage resistance.

[0027] Furthermore, since the upper end of the second throttle portion 74 provided on the inner flow plate 71 is located lower than the upper end of the inner flow plate 71, part of the lean mixture that flows into the region of the lean flame port 2 between the pair of inner flow plates 71, 71 flows around at a low speed above the second throttle portion 74 of the inner flow plate 71. As a result, a short and stable flame is formed above the second throttle portion 74 of the inner flow plate 71, and a flame stabilization effect is achieved.

[0028] In addition, in this embodiment, a plurality of introduction holes 75 are provided at intervals in the front-to-rear direction in a portion other than the first throttling portion 73 of the outer stabilizing plate 72, which is the stabilizing plate on the outer side of the stabilizing member 7, and are positioned below the lower end of the second throttling portion 74 to introduce a portion of the lean mixture into the gap portion 3. In this embodiment, no introduction holes 75 are provided directly below each of the second throttling portions 74, but it is also possible to provide introduction holes 75 in this portion.

[0029] If excess air in the lean mixture is supplied to the rich mixture ejected from the rich flame port 4, and the position where the excess air ratio becomes 1.0 becomes higher, the base of the rich flame formed by the combustion of the rich mixture, on the lean flame port 2 side, becomes unstable, causing oscillatory combustion at a relatively low frequency of 60 Hz to 80 Hz, which may result in combustion noise. In this embodiment, the lean mixture is introduced into the gap 3 through the introduction hole 75, and the position where the excess air in the lean mixture is supplied to the rich mixture and the excess air ratio becomes 1.0 is lowered by the supply of the lean mixture from the gap 3. Therefore, combustion noise caused by oscillatory combustion at a relatively low frequency of 60 Hz to 80 Hz can be suppressed.

[0030] Although the embodiments of the present invention have been described above with reference to the drawings, the present invention is not limited thereto. For example, in the above embodiment, a pair of rich flame ports 4, 4 are provided on both lateral sides of the light flame port 2, sandwiching a gap 3, 3, but the present invention can also be applied to a rich-lean burner in which a rich flame port is provided on only one lateral side of the light flame port, sandwiching a gap.

[0031] Furthermore, unlike the above embodiment, the pair of inner flow straightening plates 71, 71 may not be provided with the second throttling portion 74, and the pair of outer flow straightening plates 72, 72 may be provided with the second throttling portion 74. Even in this case, the flame formed above the gap 3 due to the combustion of an air-fuel mixture with an excess air ratio of about 1.0 is broken down more finely than in the case where only the first throttling portion 73 is provided in the flow straightening member 7, and the occurrence of resonant vibration with a frequency of about 200 Hz to 250 Hz can be suppressed to some extent.

[0032] Furthermore, although the rectifying member 7 in the above embodiment has four rectifying plates, it may have six rectifying plates, including a pair of inner rectifying plates, a pair of intermediate rectifying plates, and a pair of outer rectifying plates. In this case, if the position of the second throttling portion provided on the outer rectifying plate is shifted upward so that its upper end reaches the upper end of the outer rectifying plate, the position of the second throttling portion provided on the intermediate rectifying plate is shifted downward so that its upper end is located below the upper end of the outer rectifying plate, and the position of the second throttling portion provided on the inner rectifying plate is shifted upward so that its upper end reaches the upper end of the inner rectifying plate, then the upper part of the second throttling portion provided on the outer rectifying plate will be higher than the upper end of the second throttling portion provided on the intermediate rectifying plate. The second throttling portion provided on the pair of inner flow plates is in close contact with a portion of the inner flow plate below the lower end of the second throttling portion provided on the inner flow plate, dividing the area of the thin flame port between the outer flow plate and the intermediate flow plate into front and rear, and the lower part of the second throttling portion provided on the intermediate flow plate is in close contact with a portion of the inner flow plate below the lower end of the second throttling portion provided on the inner flow plate, dividing the area of the thin flame port between the intermediate flow plate and the inner flow plate into front and rear, and the second throttling portions provided on the pair of inner flow plates are in close contact with each other, dividing the area of the thin flame port between the two inner flow plates into front and rear. Note that the position of the second throttling portion provided on the outer flow plate may be shifted downward, the position of the second throttling portion provided on the intermediate flow plate may be shifted upward, and the position of the second throttling portion provided on the inner flow plate may be shifted downward. [Explanation of symbols]

[0033] 1...thick / light burner, 2...light flame port, 3...gap portion, 4...strong flame port, 5...burner body, 51...side plate, 6...burner cap, 61...side plate, 7...straightening member, 71...inner straightening plate, 72...outer straightening plate (laterally outermost straightening plate), 73...first throttling portion, 74...second throttling portion, 75...introduction hole.

Claims

1. A lean burner having, at its upper end, a lean flame port elongated in the front-rear direction for ejecting a lean mixture having a fuel concentration leaner than the stoichiometric air-fuel ratio, and a rich flame port adjacent to at least one lateral side of the lean flame port with a gap of a predetermined width therebetween for ejecting a rich mixture having a fuel concentration richer than the stoichiometric air-fuel ratio, A straightening member is provided with a plurality of straightening plates that divide the thin flame port into a plurality of regions in the horizontal direction, and first constriction portions are provided at a plurality of positions in front and behind the straightening member, by bringing the plurality of straightening plates into close contact with each other at the top of these straightening plates, and dividing the thin flame port into a plurality of front and rear portions, A plurality of straightening plates, including the horizontally outermost straightening plate adjacent to the gap portion, are provided with second throttling portions that are in close contact with horizontally adjacent straightening plates of each of the straightening plates and further divide each of the portions of the light flame port divided by the first throttling portions into a plurality of front and rear portions, and the lower end of the second throttling portion is located above the lower end of the first throttling portion and the vertical length is shorter than that of the first throttling portion, Furthermore, the thick-and-light burner is characterized in that the second throttle portion provided on at least some of the plurality of straightening plates has a width in the front-to-rear direction narrower than that of the first throttle portion.

2. A lean burner having, at its upper end, a lean flame port elongated in the front-to-rear direction for spraying a lean mixture having a fuel concentration leaner than the theoretical air-fuel ratio, and a rich flame port adjacent to at least one lateral side of the lean flame port across a gap of a predetermined width for spraying a rich mixture having a fuel concentration richer than the theoretical air-fuel ratio, A straightening member is provided with a plurality of straightening plates that divide the thin flame port into a plurality of regions in the horizontal direction, and first constriction portions are provided at a plurality of positions in front and behind the straightening member, by bringing the plurality of straightening plates into close contact with each other at the top of these straightening plates, and dividing the thin flame port into a plurality of front and rear portions, A plurality of straightening plates, including the horizontally outermost straightening plate adjacent to the gap portion, are provided with second throttling portions that are in close contact with horizontally adjacent straightening plates of each of the straightening plates and further divide each of the portions of the light flame port divided by the first throttling portions into a plurality of front and rear portions, and the lower end of the second throttling portion is located above the lower end of the first throttling portion and the vertical length is shorter than that of the first throttling portion, Furthermore, the thick-and-thin burner is characterized in that the upper ends of the second throttle portions provided on at least some of the plurality of straightening plates are located below the upper ends of the straightening plates.

3. A light-and-shape burner as described in claim 2, characterized in that the positions of the second throttling portion provided on one of the two adjacent straightening plates on the outer and inner sides in the horizontal direction and the second throttling portion provided on the other straightening plate are offset in the vertical direction within a range shorter than the vertical length of the second throttling portion, and the upper end of the second throttling portion provided on one straightening plate reaches the upper end of the straightening plate, but the upper end of the second throttling portion provided on the other straightening plate is located below the upper end of the straightening plate.

4. A rich-lean burner as described in any one of claims 1 to 3, characterized in that a plurality of inlet holes for introducing a portion of the lean mixture into the gap are provided at intervals in the front-to-rear direction in a portion other than the first throttling portion of the outermost horizontal straightening plate, positioned below the lower end of the second throttling portion.

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