High-temperature multi-stage cracking type combustion burner

Abstract

The utility model discloses a high-temperature multi-stage cracking type combustion burner. An oil spraying head can automatically adjust the fuel oil atomization effect according to different working conditions. The oil spraying head comprises a first-stage air inlet and a second-stage air inlet, and the air flow is adjusted through movement of an internal pushing block so as to meet the combustion requirements under different loads; and a cleaning mechanism is further arranged and used for removing impurities on the inner wall of the shell, the oil spraying holes are kept unblocked, and long-term stable operation of the combustor is guaranteed. In addition, the combustor further comprises a diffusion net and an ignition needle, the diffusion net is used for evenly distributing fuel oil, the combustion efficiency and the heat output stability are improved, the adaptability of the combustor to different working conditions is enhanced, generation of harmful emissions is reduced, and therefore dual improvement of environmental protection and economic benefits is achieved. The utility model aims to solve or alleviate the problem that oil is not uniformly distributed on a diffusion net due to the fact that an oil spraying head of an existing burner cannot adjust the atomization effect in a self-adaptive mode.

Description

Technical Field

[0001] The utility model relates to the technical field of automobile parts, in particular to a high-temperature multi-stage cracking combustion burner. Background Art

[0002] A parking heater is an auxiliary heating device that provides warm air or hot water to a parked vehicle. It is particularly suitable for commercial vehicles such as trucks and RVs. It generates heat by burning fuel (such as diesel or gasoline), which is then transferred to the air or water to achieve heating. The burner in the parking heater is the core component of the device, responsible for efficiently and safely burning the fuel to generate heat for heating.

[0003] In traditional parking heater designs, the burner typically injects fuel directly from the outlet pipe onto the diffuser. Due to a lack of precise fuel atomization control, the fuel cannot be evenly distributed across the diffuser, resulting in incomplete combustion and poor thermal efficiency. Furthermore, uneven fuel distribution can cause localized overheating or unstable combustion, increasing the production of harmful emissions such as carbon monoxide and unburned hydrocarbons. Over long-term operation, uneven combustion can damage the diffuser, reducing the equipment's service life.

[0004] If a conventional fuel injector is added to the burner, the fuel-air mixture cannot be maintained optimally under varying operating conditions. This results in insufficient fuel atomization at low loads, incomplete combustion, and increased harmful emissions. At high loads, however, excessive fuel injection wastes fuel and increases emissions. Furthermore, the inability of the fuel injector to automatically adjust the atomization effect limits the burner's adaptability to varying operating conditions, reducing the equipment's overall performance and compliance with environmental standards. Utility Model Content

[0005] The purpose of the utility model is to solve or alleviate the problem of the existing burner that the oil spray head cannot adaptively adjust the atomization effect, resulting in uneven distribution of oil on the diffusion network, and propose a high-temperature multi-stage cracking combustion burner.

[0006] The utility model is achieved through the following technical solutions:

[0007] A high-temperature multi-stage cracking combustion burner is provided with an air inlet cover, a distributor, a fixed mounting seat and a combustion guide tube along the direction of the flame. The upper end of the distributor is connected to the air inlet cover, the outer wall of the distributor is fixed with a fixed mounting seat, and the lower end of the distributor is fixed with a combustion guide tube. It also includes an oil inlet pipe and a cannula. The oil outlet end of the oil inlet pipe and the outlet end of the cannula are respectively connected to the inside of the distributor; an ignition mechanism for igniting fuel is provided in the cannula; an oil injection pipe and an oil injection head are also provided at the oil outlet end of the oil inlet pipe, one end of the oil injection pipe is connected to the oil outlet end of the oil inlet pipe, and the other end of the oil injection pipe is connected to the oil injection head; along the fuel injection direction, the outer wall of the shell of the oil injection head is provided with The first-level air inlet and the second-level air inlet, the flow cross-section of the second-level air inlet is larger than the flow cross-section of the first-level air inlet; a push block is slidingly provided in the shell, and a buffer mechanism is provided between the push block and the end of the fuel injection pipe; along the fuel injection direction, the push block is provided with an oil channel and an air channel that can respectively connect the oil channel with the first-level air inlet or the second-level air inlet; the push block is also provided with a cleaning mechanism for scraping impurities off the inner wall of the shell; the fuel flow puts pressure on the push block, and in the initial state, the air channel of the push block is connected with the first-level air inlet. As the pressure increases and offsets the restoring force of the buffer mechanism, the push block is displaced and the air channel is connected with the second-level air inlet, while driving the scraper ring to remove impurities on the inner wall of the shell.

[0008] The introduction of an injector with adjustable atomization solves the problems of uneven fuel atomization and low combustion efficiency in traditional burners under varying operating conditions. By providing air inlets of varying sizes on the outer wall of the injector housing and utilizing a linkage mechanism between the push block and the air duct, the air flow rate is automatically adjusted according to changes in fuel injection pressure, thereby optimizing the fuel-air mixture ratio. Furthermore, a cleaning mechanism is incorporated within the injector to regularly remove impurities from the inner wall of the housing, maintaining unobstructed flow of the fuel injection holes and further ensuring the burner's stability and efficient combustion under various operating conditions. Through these innovative approaches, the burner improves combustion efficiency, reduces harmful emissions, and enhances adaptability to varying load conditions, providing significant technical improvements in the actual use of parking heaters.

[0009] Preferably, the ignition mechanism includes an ignition needle and a diffusion screen. The diffusion screen and ignition needle are positioned within the combustion guide tube, facing the direction of the flame. The diffusion screen is fixedly attached to the inner wall of the combustion guide tube. One end of the ignition needle is connected to a wire that passes through a cannula, and the other end of the ignition needle contacts the surface of the diffusion screen. The diffusion screen facilitates even diffusion of the fuel within the combustion chamber, while the ignition needle ignites the fuel on the diffusion screen.

[0010] Preferably, along the fuel injection direction, the cleaning mechanism includes a scraper ring, the housing is cylindrical, the scraper ring matches the inner wall of the housing and is arranged below the push block, in order to remove impurities and carbon deposits accumulated on the inner wall of the fuel injection head housing and ensure the smooth flow of the fuel injection hole.

[0011] Preferably, the buffer mechanism includes a groove arranged above the push block and a spring arranged inside the groove, and the two ends of the spring are fixedly connected to the connecting head and the inner wall of the groove respectively; when the spring is in the initial state, the airway is connected to the first-level air inlet.

[0012] Preferably, a connector is provided between the end of the fuel injection pipe and the push block, and the upper and lower ends of the connector are respectively connected to the end of the fuel injection pipe and the housing; the two ends of the spring are respectively fixedly connected to the connector and the push block.

[0013] Preferably, a fire-holding plate is provided below the diffusion net. The fire-holding plate is fixedly connected to the inner wall of the combustion guide tube and has a hole in the middle to provide a combustion space for the flame.

[0014] Preferably, the inner diameter of the scraper ring gradually increases in the oil flowing direction.

[0015] Preferably, a guide block is further provided in the housing, and a channel with a gradually decreasing cross-sectional area is provided on the guide block in the direction of fuel flow.

[0016] Preferably, the thickness of the scraper ring is L1, the vertical distance between the axes of the primary air inlet and the secondary air inlet is L2, and L1≤L2 is satisfied.

[0017] Preferably, the cross-sectional shapes of the primary air inlet and the secondary air inlet are both circular, and the radius of the secondary air inlet is 1.5 times the radius of the primary air inlet.

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0019] 1. This utility model utilizes a pusher block and airway linkage within the injector head to automatically adjust air flow based on changes in fuel injection pressure. This allows for optimal air flow under varying load conditions, such as supplying an appropriate amount of air through the primary intake at low loads and switching to the secondary intake to increase air supply at high loads. This ensures complete fuel combustion and efficient heat conversion. Furthermore, a cleaning mechanism within the injector head regularly removes impurities from the inner wall of the housing, maintaining unobstructed flow through the injection holes and further ensuring burner stability and efficient combustion under various operating conditions.

[0020] 2. This utility model utilizes a scraper ring and diffuser screen within the injector head to effectively remove impurities and carbon deposits from the inner wall of the housing, ensuring unobstructed flow of the injector holes and preventing uneven combustion and equipment failures caused by blockage. Furthermore, the diffuser screen and ignition needle ensure even fuel distribution and effective ignition, further improving combustion efficiency and reducing harmful emissions. This ensures the burner maintains efficient and stable operation over the long term, extending the equipment's service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention.

[0022] In the attached figure:

[0023] Figure 1 This is the overall structural diagram of the combustion chamber of the present utility model;

[0024] Figure 2 This is a top view of the combustion chamber of the present invention (the air inlet cover is not shown);

[0025] Figure 3 This is a cross-sectional view of the combustion chamber of the present utility model;

[0026] Figure 4 This is a cross-sectional view of the fuel injector of the present invention, which is intended to show the state in which the air passage is connected to the first-stage air inlet;

[0027] Figure 5 This is a cross-sectional view of the fuel injection head of the present invention, intended to show the state in which the air passage is connected to the secondary air inlet.

[0028] The reference numerals represent:

[0029] 1, combustion guide tube, 2, air inlet cover, 21, air inlet, 3, distributor, 31, oil inlet pipe, 32, insert tube, 4, fixed mounting seat, 5, air inlet guide tube, 51, fire collecting plate, 6, diffusion net, 61, ignition needle, 7, oil injection head, 71, connecting head, 711, primary air inlet, 72, shell, 722, secondary air inlet, 77, push block, 771, spring, 772, scraper ring, 74, guide block. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without the need for creative work are within the scope of protection of the present invention. The schematic implementation methods of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention. It should be noted that the present invention is already in the actual research and development and use stage.

[0031] Unless otherwise defined, technical or scientific terms used in this utility model should have the ordinary meaning understood by people with ordinary skills in the field to which this utility model belongs. The words "first", "second" and similar terms used in this utility model do not indicate any order, quantity or importance, but are simply used to distinguish different components. The words "include" or "comprising" and similar words mean that the elements or objects listed before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0032] In traditional parking heater burners, fuel is typically injected directly from the outlet pipe onto the diffuser, lacking precise fuel atomization control. This design results in uneven fuel distribution, affecting combustion efficiency and increasing the production of harmful emissions such as carbon monoxide and unburned hydrocarbons. Long-term operation can also damage the diffuser due to uneven combustion, reducing the lifespan of the equipment. Even if a fuel injector is added to the burner, significant problems remain if the injector cannot automatically adjust the atomization effect according to the fuel output. Under different operating conditions, the fuel-air mixture ratio cannot be maintained at an optimal state, resulting in insufficient fuel atomization and incomplete combustion at low loads, and excessive fuel injection at high loads, causing waste and increased emissions.

[0033] Example 1:

[0034] Please refer to the attached Figure 1 -Attached Figure 4, a high-temperature multi-stage cracking combustion burner, along the direction of the flame, respectively provided with an air inlet cover 2, a distributor 3, a fixed mounting seat 4 and a combustion guide tube 1, the upper end of the distributor 3 is connected to the air inlet cover 2, the outer wall of the distributor 3 is fixed with a fixed mounting seat 4, the lower end of the distributor 3 is fixed with a combustion guide tube 1, and also includes an oil inlet pipe 31 and a plug 32, the oil outlet end of the oil inlet pipe 31 and the outlet end of the plug 32 are respectively connected to the inside of the distributor 3; the plug 32 is provided with an ignition mechanism for igniting fuel; an oil injection pipe and an oil injection head 7 are also provided at the oil outlet end of the oil inlet pipe 31, one end of the oil injection pipe is connected to the oil outlet end of the oil inlet pipe 31, and the other end of the oil injection pipe is connected to the oil injection head 7; along the fuel injection direction, the outer wall of the shell 72 of the oil injection head 7 is provided with a first-level air inlet 7 in sequence 11 and the secondary air inlet 722, the flow cross-section of the secondary air inlet 722 is larger than the flow cross-section of the primary air inlet 711; a push block 77 is slidingly provided in the shell 72, and a buffer mechanism is provided between the push block 77 and the end of the injection pipe; along the fuel injection direction, an oil channel and an air channel that can respectively connect the oil channel with the primary air inlet 711 or the secondary air inlet 722 are provided on the push block 77; a cleaning mechanism for scraping impurities from the inner wall of the shell 72 is also provided on the push block 77; the fuel flow puts pressure on the push block 77, and in the initial state, the air channel of the push block 77 is connected with the primary air inlet 711, and as the pressure increases and offsets the restoring force of the buffer mechanism, the push block 77 is displaced and the air channel is connected with the secondary air inlet 722, while driving the scraper ring to clean impurities from the inner wall of the shell 72.

[0035] Fuel is delivered to the injector head 7 through the fuel inlet pipe 31 and the injection pipe. The injector head 7 regulates the atomization of the fuel through its internal pusher block 77 and air channel. Pusher block 77 moves under the influence of fuel pressure. Initially, the air channel communicates with the primary air inlet 711. As fuel pressure increases, pusher block 77 shifts, switching the air channel to the secondary air inlet 722, thereby changing the fuel-air mixture ratio. Simultaneously, a cleaning mechanism on pusher block 77 scrapes impurities from the inner wall of the housing 72, ensuring proper operation of the injector head 7.

[0036] During the combustion process, when more air is needed to support a greater load or more complete combustion, the larger secondary air inlet 722 can provide sufficient air flow to ensure that the mixture ratio of fuel and air reaches the optimal state, allowing the burner to flexibly adjust the air supply according to different combustion requirements, thereby improving combustion efficiency and heat output.

[0037] The process of achieving secondary combustion involves two main stages. First, primary combustion occurs in the initial area of the combustion chamber. Here, fuel sprayed from the fuel injector (7) mixes with air and is ignited by the ignition needle, beginning combustion. This primary combustion converts the majority of the fuel into usable heat energy, while also producing a certain amount of high-temperature flue gas. The high-temperature flue gas then enters the secondary combustion area of the combustion chamber. Due to the higher temperature, unburned hydrocarbons and other combustible materials in the flue gas undergo a secondary combustion process in the presence of ample oxygen. This secondary combustion further improves combustion efficiency, ultimately producing cleaner exhaust gas.

[0038] As attached Figure 3 As shown, as a further preference of this embodiment, the ignition mechanism includes an ignition needle and a diffusion net 6; along the direction of the flame, a diffusion net 6 and an ignition needle are respectively provided in the combustion guide tube 1, and the diffusion net 6 is fixedly connected to the inner wall of the combustion guide tube 1. One end of the ignition needle is connected to a wire, which passes through the insert tube 32, and the other end of the ignition needle contacts the surface of the diffusion net 6.

[0039] It should be noted that the purpose of providing the diffuser mesh 6 and ignition pins is to ensure uniform fuel distribution and effective ignition. The diffuser mesh 6 facilitates even diffusion of the fuel within the combustion chamber, while the ignition pins are responsible for igniting the fuel on the diffuser mesh 6. When using the diffuser mesh 6 and ignition pins, care must be taken to ensure good contact between the ignition pins and the diffuser mesh 6 to ensure reliable ignition. Furthermore, the diffuser mesh 6 must possess sufficient strength and heat resistance to withstand long-term high-temperature operating environments.

[0040] As attached Figure 4 With attached Figure 5 As shown, as a further preference of this embodiment, along the fuel injection direction, the cleaning mechanism includes a scraper ring 772 , the housing 72 is cylindrical, the scraper ring 772 matches the inner wall of the housing 72 and is arranged below the push block 77 .

[0041] It should be noted that the scraper ring 772 is provided to remove impurities and carbon deposits accumulated on the inner wall of the housing 72 of the fuel injector 7, ensuring unobstructed flow of the fuel injection holes. The scraper ring 772 closely fits the inner wall of the housing 72, effectively scraping away deposits within the housing 72, preventing clogging of the fuel injection holes and thus maintaining fuel atomization quality.

[0042] This embodiment has a better solution. The buffer mechanism includes a groove above the push block 77 and a spring 771 inside the groove. The two ends of the spring 771 are fixedly connected to the connecting head 71 and the inner wall of the groove respectively; when the spring 771 is in the initial state, the airway is connected to the first-level air inlet 711.

[0043] This embodiment has a better solution. A connector 71 is provided between the end of the fuel injection pipe and the push block 77. The upper end and the lower end of the connector 71 are respectively connected to the end of the fuel injection pipe and the housing 72; the two ends of the spring 771 are respectively fixedly connected to the connector 71 and the push block 77.

[0044] It should be noted that connector 71 ensures a stable connection between the fuel injection pipe and push block 77, while allowing a certain degree of freedom of movement to accommodate the displacement of push block 77 during operation. This ensures that fuel injector 7 maintains good atomization effect under different operating conditions, while also ensuring the stability and reliability of the entire fuel supply system.

[0045] As attached Figure 3 As shown, this embodiment offers a more advanced solution. A flame-controlling plate 51 is provided below the diffusion net 6. This plate is fixedly attached to the inner wall of the combustion guide tube 1 and has a central opening to provide combustion space for the flame. This plate guides the flow of the flame, ensuring even distribution within the combustion chamber and improving combustion efficiency. It also helps control the shape and size of the flame, preventing it from directly impacting the combustion chamber walls, thereby reducing thermal stress and extending the service life of the combustion chamber.

[0046] Example 2:

[0047] As attached Figure 3 With attached Figure 4 As shown, as a further optimization of the above embodiment, the inner diameter of the scraper ring 772 gradually increases in the direction of fuel flow. The continuously increasing inner diameter of the scraper ring 772 forms a wedge shape, which helps to more effectively remove impurities by increasing the pressure difference during the movement of the push block 77, ensuring the cleanliness and normal operation of the fuel injector head 7.

[0048] The housing 72 is also equipped with a guide block 74, which features a channel with a gradually decreasing cross-sectional area as the fuel flows. The scraper ring has a thickness of L1, and the perpendicular distance between the primary air inlet 711 and the secondary air inlet 722 is L2, satisfying the condition L1 ≤ L2. This ensures that the scraper ring effectively removes impurities from the inner wall of the housing 72 during the movement of the push block 77. As the push block 77 moves, the pressure differential between the scraper ring and the inner wall of the housing 72 increases with distance, facilitating more thorough impurity removal. This design ensures that the injector head 7 maintains excellent cleanliness regardless of its operating conditions.

[0049] Both the primary and secondary air inlets 711 and 722 have circular cross-sections. The radius of the secondary air inlet 722 is 1.5 times that of the primary air inlet 711. This is designed to accommodate air flow requirements under varying operating conditions. The smaller air inlet (primary air inlet 711) provides an appropriate amount of air during low loads or during the initial combustion phase, ensuring adequate fuel atomization and combustion. As the load increases, the larger air inlet (secondary air inlet 722) provides more air, supporting more complete combustion and higher heat output. This design allows the burner to flexibly adjust air supply according to varying operating conditions, thereby improving combustion efficiency and heat output.

[0050] The above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present disclosure. The following points need to be explained: The accompanying drawings of the embodiments of the present invention only involve structures related to the embodiments of the present invention, and other structures can refer to the general design. In the absence of conflict, the features of the same embodiment and different embodiments of the present invention can be combined with each other. The above is only an exemplary implementation of the present invention, and is not intended to limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the attached claims.

Claims

1. A high-temperature multi-stage cracking combustion burner, which is respectively provided with an air inlet cover (2), a distributor (3), a fixed mounting seat (4) and a combustion guide tube (1) along the flame direction, wherein the upper end of the distributor (3) is connected to the air inlet cover (2), the outer wall of the distributor (3) is fixed with the fixed mounting seat (4), and the lower end of the distributor (3) is fixed with the combustion guide tube (1), characterized in that: It also includes an oil inlet pipe (31) and a plug pipe (32), the oil outlet end of the oil inlet pipe (31) and the outlet end of the plug pipe (32) are respectively connected to the inside of the distributor (3); an ignition mechanism for igniting fuel is provided in the plug pipe (32); an oil injection pipe and an oil injection head (7) are also provided at the oil outlet end of the oil inlet pipe (31), one end of the oil injection pipe is connected to the oil outlet end of the oil inlet pipe (31), and the other end of the oil injection pipe is connected to the oil injection head (7); Along the fuel injection direction, the outer wall of the shell (72) of the fuel injection head (7) is provided with a first-stage air inlet (711) and a second-stage air inlet (722) in sequence, and the flow cross section of the second-stage air inlet (722) is larger than the flow cross section of the first-stage air inlet (711); a push block (77) is provided in the shell (72) for sliding, and a buffer mechanism is provided between the push block (77) and the end of the fuel injection pipe; along the fuel injection direction, the push block (77) is provided with an oil channel and a second-stage air inlet (722) that can respectively connect the oil channel and the first-stage air inlet (711) 711) or the air passage of the secondary air inlet (722); the pushing block (77) is also provided with a cleaning mechanism for scraping impurities from the inner wall of the housing (72); the fuel flow applies pressure to the pushing block (77), and in the initial state, the air passage of the pushing block (77) is connected to the primary air inlet (711), and as the pressure increases and offsets the restoring force of the buffer mechanism, the pushing block (77) is displaced and the air passage is connected to the secondary air inlet (722), while driving the cleaning mechanism to remove impurities from the inner wall of the housing (72).

2. A high-temperature multi-stage cracking combustion burner according to claim 1, characterized in that: The ignition mechanism includes an ignition needle and a diffusion net (6); along the direction of the flame, the diffusion net (6) and the ignition needle are respectively provided in the combustion guide tube (1); the diffusion net (6) is fixedly connected to the inner wall of the combustion guide tube (1); one end of the ignition needle is connected to a wire, the wire passes through the insert tube (32), and the other end of the ignition needle contacts the surface of the diffusion net (6).

3. The high-temperature multi-stage cracking combustion burner according to claim 1, characterized in that: Along the fuel injection direction, the cleaning mechanism includes a scraper ring (772), the housing (72) is cylindrical, the scraper ring (772) matches the inner wall of the housing (72) and is arranged below the push block (77).

4. A high-temperature multi-stage cracking combustion burner according to claim 2, characterized in that: The buffer mechanism comprises a groove provided above the push block (77) and a spring (771) provided inside the groove, with both ends of the spring (771) fixedly connected to the connector (71) and the inner wall of the groove, respectively; when the spring (771) is in an initial state, the airway is communicated with the first-stage air inlet (711).

5. A high-temperature multi-stage cracking combustion burner according to claim 4, characterized in that: A connector (71) is provided between the end of the fuel injection pipe and the push block (77), and the upper end and lower end of the connector (71) are respectively connected to the end of the fuel injection pipe and the housing (72); and the two ends of the spring (771) are respectively fixedly connected to the connector (71) and the push block (77).

6. A high-temperature multi-stage cracking combustion burner according to claim 2, characterized in that: A fire-holding plate (51) is further provided below the diffusion net (6). The fire-holding plate (51) is fixedly connected to the inner wall of the combustion guide tube (1) and has a hole in the middle to provide a combustion space for the flame.

7. The high-temperature multi-stage cracking combustion burner according to claim 3, characterized in that: In the direction of fuel flow, the inner diameter of the scraper ring (772) gradually increases.

8. The high-temperature multi-stage cracking combustion burner according to claim 7, characterized in that: A guide block (74) is further provided in the housing (72), and a channel with a gradually decreasing cross-sectional area is provided on the guide block (74) in the direction in which the fuel flows.

9. The high-temperature multi-stage cracking combustion burner according to claim 3, characterized in that: The thickness of the scraper ring is L1, and the vertical distance between the axes of the first-stage air inlet (711) and the second-stage air inlet (722) is L2, and L1≤L2 is satisfied.

10. A high-temperature multi-stage cracking combustion burner according to any one of claims 1 to 9, characterized in that: The cross-sectional shapes of the primary air inlet (711) and the secondary air inlet (722) are both circular, and the radius of the secondary air inlet (722) is 1.5 times the radius of the primary air inlet (711).

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