Premixing device and combustion device comprising a premixing device

Abstract

This invention provides a premixing device and a combustion device including the premixing device. The premixing device includes: a gas flow path forming member, with the x-direction set as the axial length direction, and a Venturi-shaped gas flow path formed inside, allowing air to flow in from the outside; and a blade portion located within the gas flow path and extending along the y-direction, with a fuel gas outlet. The premixing device includes a first blade portion and a second blade portion spaced apart from each other in the z-direction, and a central air flow path is formed between these blade portions for a portion of the air to flow through. At least one of the first and second blade portions on opposite sides includes an inner bulge portion that bulges in the z-direction to reduce a portion of the central air flow path. According to this structure, a premixing device with low pressure loss and a high control ratio can be provided.

Description

Technical Field

[0001] This invention relates to a premixing device and a combustion apparatus including the premixing device. Here, "premixing" means the process of mixing air and fuel gas to generate a combustible mixture for the purpose of premixing combustion. Background Technology

[0002] As a specific example of a premixing device, there is the device described in Patent Document 1, which is shown in... Figure 9A and Figure 9B middle.

[0003] Figure 9A and Figure 9B The premixing device Ae shown includes: a tubular member 4e with a venturi-shaped gas flow path 40 formed inside; and two longitudinal and transverse blades 9A and 9B mounted on the tubular member 4e. Downstream of the gas flow path 40 ( Figure 9A The right side (not shown) is connected to the intake side of a fan, and air flows into the gas flow path 40. The gas flow path 40 is a Venturi-shaped path whose upstream area gradually decreases, while its downstream area gradually increases. (Example:) Figure 9B As shown, the two blade sections 9A and 9B are arranged in a cross shape when viewed from the side, and a fuel gas outlet 60 is provided at the rear end of the downstream side in the gas flow direction. The blade sections 9A and 9B are hollow inside, and fuel gas is supplied into the blade sections 9A and 9B from the periphery of the tubular member 4e.

[0004] In the premixing device Ae, air flows in the gas flow path 40, creating a negative pressure near the fuel gas outlet 60, thereby causing the fuel gas to flow from the fuel gas outlet 60 into the gas flow path 40 and mix with the air. Since the gas flow path 40 is venturi-shaped, the airflow rate is increased, and the negative pressure is generated.

[0005] However, there is room for improvement in the prior art, as described below.

[0006] Generally speaking, the performance requirements for premixing devices include: reducing gas pressure loss and achieving a high turndown ratio.

[0007] Here, when the air flow rate in the gas flow path 40 is high, the premixing device Ae can appropriately generate a negative pressure for the fuel gas to flow out and mix the fuel gas with air at a certain ratio. However, when the air flow rate is set to a low level, the negative pressure is not sufficiently generated, making it difficult to allow an appropriate amount of fuel gas to flow out from the fuel gas outlet 60 and mix with the air. Therefore, it is desirable to improve this situation as much as possible and obtain a high control ratio.

[0008] [Existing Technical Documents]

[0009] [Patent Literature]

[0010] [Patent Document 1] Japanese Patent Publication No. 11-502278 Summary of the Invention

[0011] [The problem the invention aims to solve]

[0012] The purpose of this invention is to provide a premixing device with low pressure loss and high control ratio, and a combustion device including the premixing device.

[0013] [Technical means to solve the problem]

[0014] To address the aforementioned issues, the following technical means are employed in this invention.

[0015] The premixing device provided by a first aspect of the present invention includes: a gas flow path forming member, wherein the x-direction is set as the axial length direction among mutually intersecting x-directions, y-directions, and z-directions, and a venturi-shaped gas flow path is formed inside which air can flow in from the outside; a blade portion located within the gas flow path and extending along the y-direction; and a fuel gas outlet disposed on the blade portion, and used to utilize the negative pressure generated when the air flowing into the gas flow path passes around the blade portion to cause fuel gas to flow out of the gas flow path and mix the fuel gas with the air; and the premixing device includes a first blade portion and a second blade portion arranged at intervals in the z-direction as the blade portion, and a central air flow path for a portion of the air to flow between these first blade portions and the second blade portion, and an inner bulge portion is included on at least one of the first blade portions and the second blade portion facing each other, the inner bulge portion bulging in the z-direction in a manner that reduces a portion of the central air flow path.

[0016] Preferably, the venturi-shaped gas flow path includes: an opening for air inflow; an upstream conical region, the inner diameter of which gradually decreases towards the rear; a small-diameter section connected to the rear side of the upstream conical region, with its inner diameter set to the minimum; and a downstream conical region connected to the rear side of the small-diameter section, the inner diameter of which gradually increases towards the rear; and the inner bulge is located in the small-diameter section.

[0017] The premixing device provided by a second aspect of the present invention includes: a gas flow path forming member, wherein the x-direction is set as the axial length direction among mutually intersecting x-directions, y-directions, and z-directions, and a venturi-shaped gas flow path is formed inside which air can flow in from the outside; a blade portion located within the gas flow path and extending along the y-direction; and a fuel gas outlet provided in the blade portion, which utilizes the negative pressure generated when the air flowing into the gas flow path passes around the blade portion to cause the fuel gas to flow out of the gas flow path and mix the fuel gas with the air; and the premixing device includes a first blade portion and a second blade portion arranged at intervals in the z-direction as the blade portion, and a pair of end-position air flow paths for a portion of the air to flow through are formed between these first blade portions and the inner wall surface of the gas flow path, and an outer bulge portion is included on the surface of the first blade portion and the second blade portion facing the inner wall surface, the outer bulge portion bulging in the z-direction in a manner that reduces a portion of the end-position air flow path.

[0018] Preferably, the venturi-shaped gas flow path includes: an opening for air inflow; an upstream conical region, the inner diameter of which gradually decreases towards the rear; a small-diameter portion connected to the rear side of the upstream conical region, with its inner diameter set to the minimum; and a downstream conical region connected to the rear side of the small-diameter portion, the inner diameter of which gradually increases towards the rear; and the outer bulge portion located in the small-diameter portion.

[0019] Preferably, the flow path area of ​​the portion of the air flow path near the end that narrows from the outer bulge is the same as the flow path area of ​​the portion of the air flow path near the center that narrows from the inner bulge.

[0020] Preferably, the first blade portion and the second blade portion each include: a pair of front inclined surfaces disposed in the forward region on the upstream side of the gas flow direction, and inclined in a rearward expanding manner with the blade thickness increasing towards the downstream side of the gas flow direction, with an included angle of acute angle; and a pair of rear inclined surfaces disposed on the rear side of the pair of front inclined surfaces, and inclined in a rearward narrowing manner with the blade thickness decreasing towards the downstream side of the gas flow direction, with an inclination angle smaller than the inclination angle of the pair of front inclined surfaces; the boundary portion between the pair of front inclined surfaces and the pair of rear inclined surfaces is the part with the maximum blade thickness, a part of the boundary portion is the inner bulge portion, and the other part is the outer bulge portion.

[0021] Preferably, a concave portion is provided at the rear end of the first blade portion and the second blade portion, which is partially recessed towards the upstream side in the gas flow direction, and the fuel gas outlet is provided in the concave portion.

[0022] The combustion apparatus provided by a third aspect of the invention includes the premixing apparatus provided by a first or second aspect of the invention.

[0023] Other features and advantages of the invention become more apparent from the following description of embodiments of the invention with reference to the accompanying drawings. Attached Figure Description

[0024] Figure 1 This is an explanatory diagram illustrating an example of a combustion apparatus including the premixing device of the present invention and a hot water supply device utilizing the same.

[0025] Figure 2 yes Figure 1 Section II-II.

[0026] Figure 3 yes Figure 1 Enlarged view of the main part.

[0027] Figure 4 yes Figure 2 A cross-sectional view of the portion of the first and second blades where the fuel gas outlet is not formed (the rounded ends of the first and second blades are omitted).

[0028] Figure 5 yes Figure 1 A schematic perspective view of the main part of the fractured tubular component of the premixing device shown.

[0029] Figure 6 yes Figure 1 Section VI-VI.

[0030] Figure 7 yes Figure 1 Section VII-VII.

[0031] Figure 8 It is a graph showing the relationship between the area ratio of the central airflow path to the end airflow path and the negative pressure of fuel gas attraction.

[0032] Figure 9A This is a cross-sectional view of the main part of an example of prior art. Figure 9B yes Figure 9A The main part, left side view. Detailed Implementation

[0033] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0034] For Figure 9A and Figure 9B Elements that are identical or similar to those in the prior art are appropriately labeled with the same symbols as those in the prior art.

[0035] Figure 1 The diagram shows a premixing device A, a combustion device B (premixed combustion device) consisting of a fan 1 and a combustion plate 2 combined in the premixing device A, and a hot water supply device WH consisting of a heat exchanger 3 combined in the combustion device B. Figure 3 yes Figure 1 Enlarged view of the main part.

[0036] In this embodiment, the x and y directions shown in the figure are both horizontal and intersect each other. The z direction is the vertical direction.

[0037] Details of the premixing device A will be described below. The premixing device A generates a mixture of air and fuel gas (combustible mixture). This mixture is ejected towards the combustion plate 2 via a fan 1. The combustion plate 2 is a porous plate with multiple vent holes 20 and is housed within a housing 10. The mixture passes through the combustion plate 2 and burns below it. The resulting combustion gases act on a heat exchanger 3, heating the hot and cold water flowing within the heat exchanger 3 to generate warm water. This warm water is then supplied to the desired hot water supply destination.

[0038] The premixing device A includes: a tubular member 4 connected to the air intake of a fan 1; a housing member 5 surrounding the tubular member 4; and a first blade portion 6A and a second blade portion 6B.

[0039] The tubular member 4 is a member in which a Venturi-shaped gas flow path 40 (equivalent to a premixing chamber) is formed inside, which is an example of the gas flow path forming member described in this invention. The axial length direction of the tubular member 4 is the x-direction. When the fan 1 is driven, external air flows into the gas flow path 40. The gas flow path 40 has the following structure: it includes an opening 40a' for air inflow, and from the upstream side to the downstream side in the gas flow direction (air flow direction), it forms an upstream conical region 40a with a gradually decreasing inner diameter, a small diameter portion 40b with the smallest inner diameter and set to be approximately constant, and a downstream conical region 40c with a gradually increasing inner diameter. In addition, unlike this embodiment, the width (width in the x-direction) of the small diameter portion 40b may be set to zero or close to zero (or it may be set to the following structure: the front end of the downstream conical region 40c is directly connected to the rear end of the upstream conical region 40a, and the boundary of these regions 40a and 40c is set as the small diameter portion 40b).

[0040] In addition to functioning as nozzles for directing fuel gas into the gas flow path 40, the first blade portion 6A and the second blade portion 6B also control the airflow in the gas flow path 40 to a suitable airflow for fuel gas outflow. These first blade portions 6A and second blade portions 6B are hollow structures comprising an internal space portion 51a serving as the fuel gas flow path and an internal cavity serving as the fuel gas outlet 60. They are positioned within the gas flow path 40, mounted on the inner wall surface 41 (the inner surface of the peripheral wall portion of the tubular member 4), and extend along the y-direction (see also...). Figure 2 , Figures 5-7 ).

[0041] Preferably, rounded portions 69 are provided at the connection points between the two ends of the first blade portion 6A and the second blade portion 6B and the inner wall surface 41 of the gas flow path 40 to suppress abrupt changes in shape. The rounded portions 69 have the effect of suppressing the airflow from becoming turbulent.

[0042] The housing member 5 serves as a fuel gas supply member for the first blade portion 6A and the second blade portion 6B. More specifically, the housing member 5 is externally fitted into the front and rear stepped portions 42a and 42b provided on the outer periphery of the tubular member 4, surrounding the tubular member 4 in a gas-tight state achieved by the sealing ring 49. A fuel gas supply port 50 is provided on the housing member 5, and the fuel gas supplied through the fuel gas supply port 50 is supplied to the fuel gas supply path 51 formed between the tubular member 4 and the housing member 5. On the other hand, as Figure 5 and Figure 6As shown, an opening 43 is formed on the tubular member 4, communicating with the internal space 51a of the first blade portion 6A and the second blade portion 6B. The fuel gas supplied by the fuel gas supply passage 51 flows into the internal space 51a of the first blade portion 6A and the second blade portion 6B through the opening 43, and then flows out from the fuel gas outlet 60 to the gas flow passage 40. Preferably, the housing member 5 includes a flange portion 53 with a bolt insertion hole 52. With this structure, the premixing device A can be easily and appropriately connected to the desired location using the flange portion 53.

[0043] The first blade portion 6A and the second blade portion 6B are arranged approximately parallel to each other, spaced apart in the vertical height direction (z-direction). Thus, a central airflow path 40A is formed between the first blade portion 6A and the second blade portion 6B. A pair of end-position airflow paths 40B are formed between the upper portion of the first blade portion 6A and the inner wall surface 41, and between the lower portion of the second blade portion 6B and the inner wall surface 41.

[0044] In this embodiment, the first blade portion 6A and the second blade portion 6B are made to have the same shape and size, and the portion where the fuel gas outlet 60 is not formed is designated as... Figure 4 The cross-sectional shape shown.

[0045] That is, in Figure 4 In the first blade portion 6A and the second blade portion 6B, a pair of forward inclined surfaces 61 are respectively located in the forward region on the upstream side of the gas flow direction, and a pair of rear inclined surfaces 62 are respectively located on the rear side. The pair of forward inclined surfaces 61 are inclined in a rearward expanding manner, with the blade thickness increasing towards the downstream side of the gas flow direction, and the included angle α is an acute angle. In contrast, the pair of rear inclined surfaces 62 are inclined in a rearward narrowing manner, with the blade thickness decreasing towards the downstream side of the gas flow direction, and the inclination angle β2 relative to the horizontal direction (x direction) is smaller than the inclination angle β1 of each of the forward inclined surfaces 61 (β1 = α / 2). The front end surface 63 of the first blade portion 6A and the second blade portion 6B is provided as a curved surface that smoothly connects the adjacent front portions of the pair of forward inclined surfaces 61 to each other. The rear end surface 64 of the first blade portion 6A and the second blade portion 6B is provided as a curved surface that smoothly connects the rear ends of the pair of rear inclined surfaces 62 to each other.

[0046] The boundary portions of a pair of front inclined surfaces 61 and a pair of rear inclined surfaces 62 in the first blade portion 6A and the second blade portion 6B are multiple bulges 65 that partially bulge upward and downward relative to the front and rear ends of the first blade portion 6A and the second blade portion 6B, and are the portions with the greatest blade thickness.

[0047] As multiple bulges 65, there is a pair of inner bulges 65a and a pair of outer bulges 65b. The pair of inner bulges 65a are upward or downward bulges provided on the opposing surfaces of the first blade portion 6A and the second blade portion 6B, and they reduce a portion of the central airflow path 40A. That is, the central airflow path 40A has the following structure: the area sandwiched by the pair of inner bulges 65a is locally reduced to an area smaller than its upstream and downstream areas.

[0048] A pair of outer bulges 65b are upward or downward bulges provided on the surfaces of the first blade portion 6A and the second blade portion 6B facing the inner wall surface 41, and each of the pair of end-position airflow paths 40B is reduced in size. That is, the pair of end-position airflow paths 40B are respectively structured such that the area opposite to the outer bulges 65b is locally reduced to an area smaller than that of its upstream and downstream areas.

[0049] The inner bulge 65a and the outer bulge 65b are located in the smallest diameter section 40b of the gas flow path 40. Preferably, the inner bulge 65a and the outer bulge 65b are located at the positions where they are provided. Figure 7 The flow area A1 of the central airflow path 40A and the flow areas A2 (A2a, A2b) of the pair of end airflow paths 40B are related as A1≒A2 (A1≒A2a≒A2b).

[0050] Fuel gas outlet 60 is located at the rear end of the central portion of the first blade portion 6A and the second blade portion 6B in the longitudinal direction (y-direction). In this embodiment, a recessed portion 66, partially recessed towards the upstream side in the gas flow direction, is provided at the rear end of the first blade portion 6A and the second blade portion 6B, and the fuel gas outlet 60 is located at the depth of the recessed portion 66 (upstream side). As described later, this structure provides the following effect: when air vortices are generated downstream of the first blade portion 6A and the second blade portion 6B in the gas flow direction, the fuel gas outflow is less likely to be adversely affected. The fuel gas outlet 60 opens towards the downstream side in the gas flow direction to minimize pressure loss caused by the fuel gas outflow from the fuel gas outlet 60.

[0051] Next, the functions of the premixing device A and the combustion device B will be explained.

[0052] First, when the fan 1 is driven, air flows into the gas flow path 40 from the opening 40a', and passes through the central air flow path 40A and a pair of end air flow paths 40B. Here, the gas flow path 40 is venturi-shaped with a small diameter portion 40b, so the air velocity is increased in the small diameter portion 40b. In addition, since the central air flow path 40A is narrowed by a pair of inner bulges 65a of the first blade portion 6A and the second blade portion 6B as described above, the air velocity is further increased in this part. In each end air flow path 40B, it is also narrowed by the outer bulges 65b of the first blade portion 6A and the second blade portion 6B, so the air velocity is also further increased in this part.

[0053] Accordingly, even when the rotational speed of fan 1 is set to a low speed and the airflow in gas passage 40 is set to a small amount, the airflow can be accelerated and a negative pressure can be appropriately generated. Therefore, by appropriately allowing fuel gas to flow out from fuel gas outlet 60 using the negative pressure, a combustible mixture of fuel gas and air in an appropriate ratio can be generated, thereby improving the control ratio.

[0054] On the other hand, the first blade portion 6A and the second blade portion 6B are located within the gas flow path 40 and extend along the y-direction, but these can be configured as follows: (as reference) Figure 4 The thin-walled structure, as described, does not pose a significant drag on airflow. Therefore, it also reduces pressure loss.

[0055] Figure 8 Showing the reference Figure 7 The negative suction pressure generated when the ratio of the flow area A1 and flow area A2 of the central air flow path 40A and each end air flow path 40B changes to 1:2, 1:1, and 2:1, respectively.

[0056] according to Figure 8 The data shown indicates that setting the ratio of flow path area A1 to flow path area A2 to 1:1 results in the lowest possible suction negative pressure. This is presumably because, at this ratio of 1:1, air will not flow with significant deviations through the central airflow path 40A and the end airflow paths 40B, thus efficiently achieving the Venturi effect at each location in both the central and end airflow paths 40A.

[0057] In contrast, in the premixing device A of this embodiment, as described above, the flow path areas A1 and A2 are set to be approximately equal, with a structure close to the 1:1 ratio. Therefore, it is more preferable in terms of maximizing the negative pressure effect of fuel gas attraction caused by the Venturi effect, and the adjustment ratio can be further improved.

[0058] In the vicinity of the downstream side of the gas flow direction of the first blade portion 6A and the second blade portion 6B, air vortices may be generated. In contrast, since the fuel gas outlet 60 is located in the concave portion 66 at the rear end of the first blade portion 6A and the second blade portion 6B, vortices are less likely to exert their influence near the fuel gas outlet 60. Therefore, the obstruction of fuel gas flow from the fuel gas outlet 60 by vortices can be suppressed, and smooth fuel gas flow can be achieved. This also improves the control ratio.

[0059] This invention is not limited to the embodiments described herein. Various design changes can be freely made to the specific structure of the premixing device and the combustion device including the premixing device, within the scope of the invention's intent.

[0060] In the described embodiment, in addition to narrowing the central airflow path 40A using the inner bulge 65a, the outer bulge 65b also narrows the end airflow paths 40B, thus further enhancing the negative pressure for fuel gas outflow. However, the present invention is not limited to this. In the present invention, it is also possible to configure a structure that narrows one of the central airflow path and the end airflow path without narrowing the other. Even in this case, compared to Patent Document 1, the negative pressure for fuel gas outflow can be enhanced, achieving the intended effect of the present invention. Furthermore, as the mechanism for narrowing the central airflow path, the inner bulge may not be provided on either the first blade portion or the second blade portion, or the inner bulge may be provided only on either the first blade portion or the second blade portion.

[0061] In this invention, the structure may also include three or more blade portions. In such cases, if at least two of the three or more blade portions have a relationship with the first and second blade portions as intended by this invention, then it is included within the scope of this invention.

[0062] In the described embodiment, the x and y directions are defined as horizontal directions, and the z direction as vertical directions. However, the invention is not limited to this. The x, y, and z directions can be any directions that intersect with each other, and can be set to directions different from those described in the embodiment.

[0063] The combustion device of the present invention is not limited to hot water supply devices; for example, it can also be used for other purposes such as heating or incineration. Furthermore, it is not limited to a type that directs the combustion gases downwards; it can also be a type that directs the combustion gases upwards, for example.

Claims

1. A premixing device, comprising: The gas flow path forming component sets the x-direction as the axial length direction among the intersecting x, y, and z directions, and forms a venturi-shaped gas flow path inside that allows air to flow in from the outside. The blade portion is located within the gas flow path and extends along the y-direction; and A fuel gas outlet is provided at the blade portion, and is used to utilize the negative pressure generated when air flows into the gas flow path and passes around the blade portion to cause fuel gas to flow out of the gas flow path and mix with the air; and The premixing device includes a first blade portion and a second blade portion, which are spaced apart from each other in the z-direction and each extends in the y-direction. The two ends of the first blade portion and the second blade portion in the y-direction are connected to the inner wall surface of the gas flow path. An air flow path is formed between the first blade portion and the second blade portion, allowing a portion of the air to flow through. The first blade portion and the second blade portion each have an inner bulge on at least one of their opposite sides, the inner bulge bulging in the z-direction in a manner that reduces a portion of the central airflow path.

2. The premixing device according to claim 1, wherein, The Venturi-shaped gas flow path includes: an opening for air inflow; an upstream conical region, the inner diameter of which gradually decreases towards the rear; a small-diameter section connected to the rear side of the upstream conical region, with its inner diameter set to the minimum; and a downstream conical region connected to the rear side of the small-diameter section, the inner diameter of which gradually increases towards the rear. The inner bulge is located in the small diameter portion.

3. The premixing device according to claim 1, wherein, A pair of end-position airflow paths are formed between the first and second blade portions and the inner wall surface of the gas flow path, allowing another portion of the air to flow through. The first and second blade portions each include an outer bulge on the surface facing the inner wall, the outer bulge bulging in the z-direction in a manner that reduces a portion of the airflow path at each end.

4. The premixing device according to claim 3, wherein, The flow area of ​​the portion of the airflow path near each end that narrows from the outer bulge is the same as the flow area of ​​the portion of the airflow path near the center that narrows from the inner bulge.

5. The premixing apparatus according to claim 3, wherein, The Venturi-shaped gas flow path includes: an opening for air inflow; an upstream conical region, the inner diameter of which gradually decreases towards the rear; a small-diameter section connected to the rear side of the upstream conical region, with its inner diameter set to the minimum; and a downstream conical region connected to the rear side of the small-diameter section, the inner diameter of which gradually increases towards the rear. The outer bulge is located in the small diameter portion.

6. The premixing apparatus according to claim 3, wherein, The first blade portion and the second blade portion respectively include: A pair of forward-sloping surfaces are located in the forward region on the upstream side of the gas flow direction, and slope backward in an expanding manner with the blade thickness increasing towards the downstream side of the gas flow direction, with an acute angle between them; and A pair of rear inclined surfaces are disposed behind the pair of front inclined surfaces, and are inclined in a way that the thickness of the blades decreases as they move downstream of the gas flow direction, with their inclination angle being smaller than that of the pair of front inclined surfaces. The boundary between the pair of front inclined surfaces and the pair of rear inclined surfaces is the part with the greatest blade thickness. Part of the boundary is the inner bulge and the other part is the outer bulge.

7. The premixing apparatus according to claim 1, wherein, The first blade portion and the second blade portion each have a recessed portion that is partially recessed towards the upstream side in the gas flow direction at their respective rear ends. The concave portion is provided with the fuel gas outlet.

8. A premixing device, comprising: The gas flow path forming component sets the x-direction as the axial length direction among the intersecting x, y, and z directions, and forms a venturi-shaped gas flow path inside that allows air to flow in from the outside. The blade portion is located within the gas flow path and extends along the y-direction; and A fuel gas outlet is provided at the blade portion, and is used to utilize the negative pressure generated when air flows into the gas flow path and passes around the blade portion to cause fuel gas to flow out of the gas flow path and mix with the air; and The premixing device includes a first blade portion and a second blade portion, which are spaced apart from each other in the z-direction and each extends in the y-direction, and the two ends of the first blade portion and the second blade portion in the y-direction are connected to the inner wall surface of the gas flow path. A pair of end-position air flow paths are formed between the first blade portion and the second blade portion and the inner wall surface of the gas flow path to allow a portion of the air to flow through. The first and second blade portions each include an outer bulge on the surface facing the inner wall, the outer bulge bulging in the z-direction in a manner that reduces a portion of the airflow path at each end.

9. The premixing apparatus according to claim 8, wherein, The Venturi-shaped gas flow path includes: an opening for air inflow; an upstream conical region, the inner diameter of which gradually decreases towards the rear; a small-diameter section connected to the rear side of the upstream conical region, with its inner diameter set to the minimum; and a downstream conical region connected to the rear side of the small-diameter section, the inner diameter of which gradually increases towards the rear. The outer bulge is located in the small diameter portion.

10. A combustion device comprising a premixing device as claimed in any one of claims 1 to 9.

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