CN111473362A - Premixing nozzle of gas turbine combustor - Google Patents

Abstract

The invention provides a gas turbine combustion chamber premixing nozzle, comprising: a central lobe fuel nozzle, an outer fuel distribution ring cavity and a premixing nozzle channel, wherein the central lobe fuel nozzle is coaxially arranged on the premixing nozzle. The inner center position of the mixing nozzle channel is used to uniformly pass the fuel into the premixing nozzle channel; the central lobe type fuel nozzle includes a hollow lobe structure formed by adjacent connection of M lobes, M≥3; A first fuel hole is arranged on the lobe structure, and the outer fuel distribution ring cavity is arranged between the central lobe type fuel nozzle and the outlet of the premix nozzle channel, and is coaxially arranged on the outer wall of the premix nozzle channel and the premix nozzle channel. communication for passing secondary fuel into the premix nozzle passage. It can improve the fuel/air mixing uniformity at the nozzle outlet, reduce the nitrogen oxide emission in the combustion chamber, improve the combustion stability, and suppress the thermoacoustic shock.

Description

A gas turbine combustor premix nozzle

technical field

The invention relates to the technical field of gas turbines, in particular to a premixing nozzle for a combustion chamber of a gas turbine.

Background technique

In order to improve the efficiency of gas turbines, the outlet temperature of the combustion chamber is getting higher and higher, and the nitrogen oxide emission under high temperature conditions increases exponentially with the increase of the outlet temperature of the combustion chamber. How to suppress the formation of nitrogen oxides under high temperature conditions is the focus and difficulty of the current combustion chamber design. The unit nozzle is an important part of the combustion chamber, and its structural design and layout play a decisive role in the combustion chamber performance and pollutant emissions. In order to meet the increasingly stringent pollutant emission standards, it is necessary to carry out a series of optimization designs for unit nozzles, including increasing blending uniformity, reducing the risk of flashback, etc., to reduce NOx emissions and suppress thermoacoustics while ensuring combustion efficiency shock.

Dry lean premixed combustion technology is currently the mainstream combustion technology in the field of gas turbines. Under the condition of constant combustion chamber outlet temperature, dry lean premixed combustion mainly reduces the generation of thermal NOx by reducing the flame peak temperature, thereby reducing the overall NOx emission. The difficulty of premixing nozzle design is to achieve rapid mixing of fuel and air in limited time and space, and the mixing quality has an important impact on combustion stability and NOx emission. With the gradual reduction of pollutant emission standards, it is still necessary to optimize the design of the nozzle structure of the existing dry lean premixed combustor to achieve stable, efficient and low-pollution operation of the gas turbine combustor.

SUMMARY OF THE INVENTION

(1) Technical problems to be solved

In view of this, the main purpose of the present invention is to provide a premixing nozzle for a gas turbine combustion chamber, which is used to improve the fuel/air mixing uniformity at the nozzle outlet, improve combustion stability while reducing nitrogen oxide emissions in the combustion chamber, and suppress Thermal shock.

(2) Technical solutions

In order to solve the above problems, the present invention provides a gas turbine combustion chamber premixing nozzle, comprising: a central lobed fuel nozzle, an outer fuel distribution ring cavity and a premixing nozzle channel, wherein the central lobed fuel nozzle is coaxial It is arranged at the inner center of the premixing nozzle channel, and is used to uniformly pass the fuel into the premixing nozzle channel; the central lobe type fuel nozzle includes a hollow lobe structure composed of M lobes connected adjacently, M≥ 3. A first fuel hole is arranged on the lobe structure, the outer fuel distribution ring cavity is arranged between the central lobed fuel nozzle and the outlet of the premixing nozzle channel, and is coaxially arranged on the outer wall of the premixing nozzle channel It communicates with the premixing nozzle passage and is used for passing the secondary fuel into the premixing nozzle passage.

Optionally, the central lobe type fuel nozzle further includes a hollow annular portion disposed at the front of the lobe structure, and a central fuel conduit disposed at the front of the hollow annular portion for introducing fuel; wherein the hollow The annular part and the cavity between the outer wall and the inner wall of the lobe structure constitute a first channel for the fuel to pass through. The end of the central fuel conduit is provided with P radial branch pipes, P≥3, and the radial branch pipes are connected to the end of the central fuel conduit. The first channel is communicated; the tail portion of the wave lobe structure is provided with a first fuel hole communicated with the first channel.

Optionally, the first fuel holes are opened on the inner wall and the outer wall of the tail portion of the lobe structure, and the first fuel holes are uniformly distributed along the circumference of the lobe structure.

Optionally, the inner diameter D ₂ of the hollow annular portion satisfies: D ₁ /3≦D ₂ ≦3/4D ₁ , where D ₁ is the inner diameter of the premixing nozzle channel.

Optionally, the distance L ₁ between the radial branch pipe and the connection between the hollow annular portion and the lobe structure satisfies: D ₂ /2≦L ₁ ≦2D ₂ , where D ₂ is the inner diameter of the hollow annular portion.

Optionally, the outer edge height H ₁ of the lobe structure satisfies: D ₂ /4≤H ₁ ≤3/4D ₂ ; the inner edge height H ₂ of the lobe structure satisfies: D ₂ /4≤H ₂ ≤3/4D ₂ ; the number N of the first fuel holes satisfies: N≧4M; wherein, D ₂ is the inner diameter of the hollow annular portion.

Optionally, the outer lobe angle θ ₁ of the lobe in the lobe structure satisfies 10°≤θ ₁ ≤30°; the inner lobe angle θ ₂ of the lobe satisfies 10°≤θ ₂ ≤30°; the sidewall of the lobe The included angle θ ₃ of the line connecting the bottom of the lobe and the axis satisfies 0.5π/M≤θ ₃ ≤2π/M.

Optionally, the second fuel holes in the outer fuel distribution ring cavity are two rows of evenly distributed holes, the two rows of holes are distributed along the circumference of the outer wall of the premix nozzle channel, and the two rows of holes are arranged in a staggered manner, The number K of holes in each row satisfies K≧6, and the distance L ₂ between the two rows of holes satisfies D ₁ /4≦L ₂ ≦D ₁ , where D ₁ is the inner diameter of the premixing nozzle channel.

Optionally, the shortest distance L ₄ between the second fuel hole in the outer fuel distribution ring cavity and the outlet section of the premixing nozzle passage satisfies D ₁ /2≦L ₄ ≦2D ₁ .

Optionally, the distance L ₃ between the tail section of the lobe structure and the outlet of the premix nozzle channel satisfies 2D ₁ ≤L ₃ ≦5D ₁ , where D ₁ is the inner diameter of the premix nozzle channel.

(3) Beneficial effects

The present invention has at least the following beneficial effects:

(1) When the external air flows through the lobed fuel nozzle provided by the present invention, a complex vortex structure (such as flow vortex, orthogonal vortex, horseshoe vortex, etc.) can be formed at the trailing edge of the lobe, thereby enhancing the downstream fuel Blending with air improves the fuel/air mixing uniformity at the outlet of the premix nozzle.

(2) Compared with the traditional swirl premixing nozzle, the premixing nozzle provided by the present invention can realize more efficient mixing of fuel and air at the nozzle outlet, and the required length of the premixing section is shorter. Therefore, the peak temperature of the jet flame is reduced, and the NOx emission is suppressed;

(3) Compared with the traditional fuel nozzle, the central fuel nozzle of the premixing nozzle adopts a lobed structure, and the gas flow in the outer flow field is smoother, which is beneficial to improve the mixing efficiency and reduce the pressure loss;

(4) The second fuel holes in the outer fuel distribution ring cavity are arranged in double rows in a staggered manner, which further improves the fuel/air mixing uniformity and suppresses the occurrence of thermoacoustic shocks; at the same time, when the equivalence ratio is low, the outer ring cavity is appropriately increased. The fuel supply ratio can appropriately increase the fuel concentration outside the jet and increase the combustion stability.

(5) The lobed fuel nozzle nozzle provided by the present invention has a compact structure and flexible adjustment, and can effectively suppress the formation of a local high temperature zone downstream of the nozzle, thereby reducing the emission of nitrogen oxides in the combustion chamber.

Description of drawings

1 is a schematic structural diagram of a gas turbine combustion chamber premixing nozzle according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view of the lobe structure of the gas turbine combustor premixing nozzle shown in FIG. 1;

3 is a cross-sectional view of the central fuel conduit and its radial branch structure of the gas turbine combustor premixing nozzle shown in FIG. 1;

Fig. 4 is the C-C plane sectional view of the central lobe type fuel nozzle of the gas turbine combustor premixing nozzle shown in Fig. 1;

5 is a D-D cross-sectional view of the central lobe fuel nozzle of the gas turbine combustor premixing nozzle shown in FIG. 1;

Fig. 6 is the E-E cross-sectional view of the outer fuel distribution ring cavity of the gas turbine combustor premixing nozzle shown in Fig. 1;

FIG. 7 is a cross-sectional view of the F-F plane of the outer fuel distribution ring cavity of the premixing nozzle of the gas turbine combustor shown in FIG. 1 .

Among them, the reference numerals are:

11- center fuel conduit; 12- center lobe fuel nozzle;

21-outer fuel distribution ring cavity fuel conduit; 22-outer fuel distribution ring cavity;

31-premix nozzle channel; 12a-lobe structure;

12b - hollow annular portion; 12c - first channel;

12d-first fuel hole; 11a-radial branch pipe;

22a - the second fuel hole;

D ₁ - the inner diameter of the premix nozzle channel (31); D ₂ - the inner diameter of the hollow annulus;

L ₁ - the distance between the radial branch pipe and the connection between the hollow annular part and the lobe structure; L ₂ - the distance between the two rows of second fuel holes in the outer fuel distribution ring cavity; L ₃ - the tail section of the lobe structure and the the distance between the outlet of the premixing nozzle passage; L ₄ - the shortest distance between the second fuel hole in the outer fuel distribution ring cavity and the outlet section of the premixing nozzle passage;

H ₁ - the height of the outer edge of the lobe structure; H ₂ - the height of the inner edge of the lobe structure;

θ ₁ - the outer lobe angle of the lobe structure; θ ₂ - the inner lobe angle of the lobe structure;

θ ₃ - the angle between the lobe side wall and the lobe bottom and the line connecting the axis.

Detailed ways

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be understood, however, that these descriptions are exemplary only, and are not intended to limit the scope of the present invention. In the following detailed description, for convenience of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present invention. It will be apparent, however, that one or more embodiments may be practiced without these specific details. Also, in the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concepts of the present invention.

The terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the present invention. The terms "comprising", "comprising" and the like as used herein indicate the presence of stated features, steps, operations and/or components, but do not preclude the presence or addition of one or more other features, steps, operations or components.

An embodiment of the present invention provides a gas turbine combustion chamber premixing nozzle, referring to FIG. 1 , comprising: a central lobe fuel nozzle 12 , an outer fuel distribution ring cavity 22 and a premixing nozzle channel 31 , wherein the central lobe type fuel nozzle 12 , and a premixing nozzle channel 31 are provided. The fuel nozzle 12 is coaxially disposed at the inner center of the premixing nozzle passage 31, and is used to uniformly pass the fuel into the premixing nozzle passage 31; the central lobed fuel nozzle 12 includes M lobes connected adjacently. The hollow lobe structure 12a, M≥3; the first fuel hole 12d is arranged on the lobe structure 12a; the lobe structure can widen the distribution range of the fuel holes in the radial space of the premixing channel, and at the same time enhance the disturbance and improve the Blending efficiency. The outer fuel distribution ring cavity 22 is arranged between the central lobed fuel nozzle 12 and the outlet of the premixing nozzle passage 31, and is coaxially arranged on the outer wall of the premixing nozzle passage 31 to communicate with the premixing nozzle passage 31, and is used to connect the premixing nozzle passage 31. The secondary fuel is passed into the premixing nozzle channel 31, which further improves the uniformity of fuel/air premixing and suppresses the generation of thermoacoustic shock.

Therefore, the present invention increases the distribution range of the fuel holes in the radial space in the channel by arranging the lobed fuel nozzle in the premixing nozzle channel, that is, the hollow lobe structure 12a is formed by connecting M lobes adjacently, and at the same time A complex vortex structure is induced downstream of the lobed fuel nozzle, which improves the mixing efficiency of fuel and air, reduces the non-uniformity of fuel-air mixing at the nozzle outlet section, and thus inhibits the formation of local hot spots in the combustion chamber. Reduced NOx emissions. In addition, by setting a fuel ring cavity downstream of the lobed fuel nozzle to supply secondary fuel, the combustion pulsation generated by different fuel incident points can cancel each other, thereby suppressing the generation of thermoacoustic oscillation; under low operating conditions, the ring cavity can be reasonably distributed by distributing the ring cavity. The fuel ratio can also improve the combustion stability of the combustion chamber at low loads. The premixing nozzle has a compact structure and is suitable for the combustion of natural gas, coal-to-synthesis gas and other low-to-medium calorific value synthesis gas.

Specifically, referring to FIGS. 1 to 7 , the central lobe type fuel nozzle 12 further includes a hollow annular portion 12b disposed at the front of the lobe structure 12a, and is disposed at the front of the hollow annular portion 12b for introducing fuel The central fuel conduit 11; wherein, the hollow annular portion 12b and the cavity between the outer wall and the inner wall of the lobed structure 12a constitute the first channel 12c for the fuel to pass through, in order to ensure that the central fuel is in the central lobed fuel The hollow annular portion 12b of the nozzle 12 is evenly distributed in the circumferential direction, and the end of the central fuel conduit 11 is provided with P radial branch pipes 11a, P≥3, the radial branch pipes 11a communicate with the first channel 12c; the wave A first fuel hole 12d communicated with the first passage 12c is provided at the tail of the petal structure 12a.

After the fuel is introduced from the front end of the central fuel conduit 11, it enters the hollow annular portion 12b through the P radial branch pipes 11a and the cavity between the outer wall and the inner wall of the lobe structure 12a constitutes a first channel 12c for the fuel to pass through, and then It flows out through the first fuel hole 12d at the rear of the lobe structure 12a and enters the premixing nozzle passage 31 .

In order to ensure the mixing efficiency, the first fuel holes 12d are opened on the inner wall and the outer wall of the tail of the lobe structure 12a, and the first fuel holes 12d are evenly distributed along the circumference of the lobe structure 12a. In addition, the inner diameter D ₂ of the hollow annular portion 12b satisfies: D ₁ /3≦D ₂ ≦3/4D ₁ , wherein D ₁ is the inner diameter of the premixing nozzle passage 31 . The distance L ₁ between the radial branch pipe 11a and the connection between the hollow annular portion 12b and the lobe structure 12a satisfies: D ₂ /2≦L ₁ ≦2D ₂ . The L ₁ is the flow distance of the fuel within the hollow annular portion.

In addition, in order to further ensure the mixing efficiency, the height H ₁ of the outer edge of the lobe structure 12a satisfies: D ₂ /4≤H ₁ ≤3/4D ₂ ; the height H ₂ of the inner edge of the lobe structure 12a satisfies: D ₂ /4≦H ₂ ≦3/4D ₂ ; the number N of the first fuel holes 12d satisfies: N≧4M.

In order to improve the mixing efficiency of the central lobed fuel nozzle 12, avoid flow separation, and reduce pressure loss, the outer lobe angle θ ₁ of the lobe in the lobe structure 12a satisfies 10°≤θ ₁ ≤30°; The inner lobe angle θ ₂ satisfies 10°≤θ ₂ ≤30°; the included angle θ ₃ between the line connecting the lobe sidewall and the lobe bottom and the axis satisfies 0.5π/M≤θ ₃ ≤2π/M.

In order to suppress the thermoacoustic oscillation during the combustion process, the second fuel holes 22a in the outer fuel distribution ring cavity 22 are two rows of evenly distributed holes, the two rows of holes are distributed along the circumference of the outer wall of the premixing nozzle channel 31, and the The two rows of holes are staggered, the number K of each row of holes satisfies K≥6, and the distance L ₂ between the two rows of holes satisfies D ₁ /4≤L ₂ ≤D ₁ , where D ₁ is premixed The inner diameter of the nozzle passage 31 . In order to ensure the uniformity of fuel distribution at the outlet, the shortest distance L ₄ between the second fuel hole 22a in the outer fuel distribution ring cavity 22 and the outlet section of the premixing nozzle passage 31 satisfies D ₁ /2≤L ₄ ≤2D ₁ . After the secondary fuel passes into the outer fuel distribution ring cavity 22 from the fuel conduit 21 of the outer fuel distribution ring cavity, it enters the premixing nozzle passage 31 through the second fuel hole 22a.

In order to ensure the uniformity of the fuel/air distribution in the outlet section of the premixing nozzle channel 31, and at the same time prevent the turbulence of the lobe from causing excessive disturbance at the channel outlet, thereby affecting the stability of the flame at the nozzle outlet, the tail of the lobe structure 12a The distance L ₃ between the cross section and the outlet of the premixing nozzle channel 31 satisfies 2D ₁ ≦L ₃ ≦5D ₁ , where D ₁ is the inner diameter of the premixing nozzle channel 31 .

In this embodiment, the outlet velocity of the premixing nozzle is set to be 80m/s to 160m/s, the jet velocity of the first fuel hole of the central lobed fuel nozzle is set to be 20m/s to 60m/s, and the second fuel in the outer fuel ring cavity is set to be 20m/s to 60m/s. The jet velocity at the hole is 40m/s to 100m/s. Under rated load conditions, through the efficient mixing of the lobe structure, rapid and uniform mixing of fuel and air is achieved, the formation of local hot spots caused by uneven mixing is reduced, and NOx emissions are reduced. At the same time, the secondary fuel introduced into the fuel ring cavity also inhibits the occurrence of thermoacoustic shock. However, under low load conditions, as the equivalence ratio decreases, the jet under fully premixed conditions will lead to a decrease in combustion stability. At this time, by appropriately increasing the fuel ratio of the outer annular cavity, the fuel concentration at the periphery of the jet is increased, thereby reducing the ignition delay time and improving the combustion stability under the condition of low equivalence ratio.

It should be noted that, in the drawings or the main text of the description, the experimental methods that are not shown or described are the forms known to those of ordinary skill in the art, and are not described in detail. In addition, the above definitions of each element are not limited to the various specific structures and shapes mentioned in the embodiments, and those of ordinary skill in the art can simply modify or replace them, for example:

(1) The second fuel hole in the outer fuel ring cavity can also adopt other forms or structures, and the number of rows of openings can also be multiple rows, as long as the same function can be accomplished;

(2) The first fuel hole of the central lobe fuel nozzle can also be inclined at an appropriate angle or set on the trailing edge surface of the lobe so that the jet direction is parallel to the axis direction, as long as the fuel-air mixing degree at the nozzle outlet can be guaranteed to meet the requirements ;

(3) Demonstrations of parameters including specific values may be provided herein, but these parameters need not be exactly equal to the corresponding values, but may be approximated within acceptable error tolerances or design constraints;

(4) Orientation words mentioned in the implementation, such as "front", "rear", etc., only refer to the direction of the accompanying drawings, and are not intended to limit the protection scope of the present invention;

To sum up, the premixing nozzle provided by the present invention makes full use of the characteristics of low pressure loss and high mixing efficiency of the lobed structure. The position of the hole greatly improves the mixing efficiency of fuel and air. At the same time, the downstream of the central lobed fuel nozzle further uses a fuel ring cavity to supply secondary fuel, which can be used to supplement the insufficient mixing of the lobed nozzle at the edge of the flow channel under rated conditions, and improve the uniformity of fuel and air distribution at the nozzle outlet. Thereby reducing NOx emissions; and under low equivalence ratio conditions, the secondary fuel can be used to increase the fuel concentration at the jet edge and increase combustion stability. At the same time, the dual-row fuel hole design of the annular cavity can also suppress the generation of thermoacoustic shock, broaden the stable operation range of the combustion chamber, and realize the rapid response of the combustion chamber to the load. The premixing nozzle has compact structure, flexible adjustment and high reliability, and can be applied to the combustion of various gas fuels such as natural gas, coal-to-synthesis gas and other medium and low calorific value synthesis gas.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in further detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A gas turbine combustor premix nozzle, comprising: a central lobe fuel nozzle (12), an outer fuel distribution annulus (22), and a premix nozzle passage (31),

the central lobe type fuel nozzle (12) is coaxially arranged at the central position in the premixing nozzle channel (31) and is used for uniformly introducing fuel into the premixing nozzle channel (31); the central lobe type fuel nozzle (12) comprises a hollow lobe structure (12a) formed by adjacent connection of M lobes, M is more than or equal to 3, and a first fuel hole (12d) is arranged on the lobe structure (12 a);

the outer fuel distribution ring cavity (22) is arranged between the central lobe type fuel nozzle (12) and an outlet of the premixing nozzle channel (31), is coaxially arranged on the outer wall of the premixing nozzle channel (31) and is communicated with the premixing nozzle channel (31) and is used for introducing secondary fuel into the premixing nozzle channel (31).

2. The combustor premix nozzle of claim 1, wherein said central lobe fuel nozzle (12) further comprises a hollow annular portion (12b) disposed forward of said lobe structure (12a), a central fuel conduit (11) disposed forward of hollow annular portion (12b) for passing fuel;

the hollow annular part (12b) and a cavity between the outer wall and the inner wall of the lobe structure (12a) form a first channel (12c) for fuel to pass through, P radial branch pipes (11a) are arranged at the tail end of the central fuel guide pipe (11), P is more than or equal to 3, and the radial branch pipes (11a) are communicated with the first channel (12 c); the tail part of the lobe structure (12a) is provided with a first fuel hole (12d) communicated with the first channel (12 c).

3. The combustor premix nozzle according to claim 2, wherein said first fuel holes (12d) open on the inner and outer walls of the aft portion of said lobed structure (12a), said first fuel holes (12d) being evenly distributed circumferentially along the lobed structure (12 a).

4. Premix nozzle according to claim 2, characterized in that the inner diameter D of the hollow annular portion (12b)₂Satisfies the following conditions: d₁/3≤D₂≤3/4D₁Wherein D is₁Is the inner diameter of the premixing nozzle passage (31).

5. Premix nozzle according to claim 2, characterized in that the distance L between the radial branch (11a) to the junction of the hollow annular portion (12b) and the lobe structure (12a)₁Satisfies the following conditions: d₂/2≤L₁≤2D₂Wherein D is₂Is the inner diameter of the hollow annular part (12 b).

6. The premix nozzle of claim 2, wherein the lobe structure (12a) has an outer rim height H₁Satisfies the following conditions: d₂/4≤H₁≤3/4D₂(ii) a The height H2 of the inner edge of the lobe structure (12a) satisfies: d₂/4≤H₂≤3/4D₂(ii) a The number N of the first fuel holes (12d) satisfies: n is more than or equal to 4M; wherein D is₂Is the inner diameter of the hollow annular part (12 b).

7. The premix nozzle of claim 1, wherein the lobe configuration (12a) has lobe angles θ₁Theta is more than or equal to 10 degrees₁Less than or equal to 30 degrees; inner lobe angle theta of lobe₂Theta is more than or equal to 10 degrees₂Less than or equal to 30 degrees; the included angle theta between the lobe side wall and the connecting line of the lobe bottom and the axis₃Satisfies the condition that 0.5 pi/M is not more than theta₃≤2π/M。

8. The premix nozzle of claim 1, wherein the outer portion is a portion of a fuel injectorThe second fuel holes (22a) in the side fuel distribution ring cavity (22) are two rows of holes which are uniformly distributed, the two rows of holes are distributed along the circumferential direction of the outer wall of the premixing nozzle channel (31), the two rows of holes are staggered, the number K of each row of holes meets the condition that K is more than or equal to 6, and the distance L between the two rows of holes₂Satisfies D₁/4≤L₂≤D₁Wherein D is₁Is the inner diameter of the premixing nozzle passage (31).

9. The premix nozzle of claim 8, wherein a shortest distance L between a second fuel hole (22a) in said outer fuel distribution annulus (22) and an outlet cross-section of said premix nozzle passage (31)₄Satisfies D₁/2≤L₄≤2D₁。

10. The premix nozzle of claim 1, wherein a distance L between an aft cross-section of said lobe structure (12a) and an outlet of said premix nozzle passage (31)₃Satisfy 2D₁≤L₃≤5D₁Wherein D is₁Is the inner diameter of the premixing nozzle passage (31).

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