A premixed hydrogen-blended natural gas fuel nozzle and a method for nozzle flashback testing.

Abstract

This invention provides a premixed hydrogen-blended natural gas fuel nozzle and a method for testing nozzle backfire. It solves the problems of increased backfire risk with increasing hydrogen blending ratio in natural gas, insufficient theoretical calculation support, and a lack of experimental methods that hinder the development of hydrogen fuel combustion technology. This invention belongs to the field of combustion chamber testing technology. The invention includes: operating the premixed hydrogen-blended natural gas fuel nozzle stably in a combustion chamber under a certain operating condition using pure natural gas fuel; measuring the reference temperature of the premixing channel; adjusting the fuel to hydrogen-blended natural gas fuel and stably burning it under the same operating condition; measuring the actual temperature of the premixing channel; performing logical judgment; if backfire occurs, the test is stopped; if no backfire occurs, the hydrogen blending ratio is adjusted and the test continues until backfire occurs. The operating condition is adjusted and the test is repeated to finally form a full-condition backfire characteristic curve, determining the maximum hydrogen blending ratio of natural gas. This invention is applicable to backfire testing and combustion chamber improvement design in the field of gas turbines with air-fuel premixing structures.

Description

Technical Field

[0001] This invention belongs to the field of combustion chamber testing, specifically relating to a premixed hydrogen-blended natural gas fuel nozzle and a nozzle backfire test method. Background Technology

[0002] Compared to natural gas, hydrogen fuel is characterized by a wider combustible range and faster flame propagation speed, making it prone to backfire. Once backfire occurs, the fuel nozzle will experience localized high-temperature erosion, cracking, and spalling, affecting the combustion chamber's service life. Severe spalling can damage turbine blades, causing significant losses. Therefore, backfire control is one of the key research areas in hydrogen fuel combustion technology. Due to the considerable complexity of pure hydrogen combustion, pure hydrogen combustion technology is currently in the early stages of mechanism research, with very few actual engineering applications. The feasible engineering approach at present is to conduct research through a gradual transition, blending hydrogen with natural gas, gradually increasing the hydrogen blending ratio, and ultimately transitioning from pure natural gas to pure hydrogen fuel. This approach fully utilizes existing natural gas industrial foundations, resources, and technological experience for a smooth transition. When natural gas is blended with hydrogen, the risk of flashback increases sharply with the increase of the hydrogen blending ratio. Although simulation calculations can be used to make preliminary flashback predictions, the effect of low accuracy, high cost and long cycle is not obvious in supporting engineering applications. Therefore, effective experimental research on the combustion of hydrogen-blended natural gas fuel is the most effective means to promote the development of hydrogen fuel combustion technology. In particular, flashback characteristic testing is a key indicator for achieving technological breakthroughs. However, there are few reports on flashback characteristic testing methods in the current public literature. Summary of the Invention

[0003] The purpose of this invention is to provide a premixed hydrogen-blended natural gas fuel nozzle and a nozzle flashback test method that offers rapid and accurate verification results, low testing costs, strong engineering applicability and good scalability, and can comprehensively and effectively evaluate flashback characteristics. This provides practical guidance for flashback characteristic testing of premixed hydrogen-blended natural gas fuel nozzles, reduces the development cost of low-emission hydrogen fuel combustion chambers, shortens the development cycle, improves the development success rate, and thus provides technical support for the stable and safe operation of gas turbines.

[0004] A premixed hydrogen-blended natural gas fuel nozzle includes a nozzle body; the nozzle body is a two-stage radial premixing structure, including a first fuel channel, a first fuel injection orifice, a first air cyclone, a second fuel channel, a second fuel injection orifice, and a second air cyclone; the first fuel injection orifice is disposed on the cyclone blades of the first air cyclone, and the second fuel injection orifice is disposed on the cyclone blades of the second air cyclone; one end of the first fuel channel and the second fuel channel are connected to a fuel inlet, and the other end is respectively connected to the first fuel injection orifice and the second fuel injection orifice; the second air cyclone is arranged around the first air cyclone to form a two-stage radial stage, and a first air-fuel premixing channel and a second air-fuel premixing channel are provided at the outlet of the two-stage air cyclone.

[0005] Furthermore, the head of the nozzle body is connected to the mounting sealing cover plate by fasteners after insertion; the mounting sealing cover plate is a cover plate structure with a central hole.

[0006] Furthermore, a lead seat is inserted into the circular stepped hole of the mounting sealing cover, and a first clamping ring, a sealing filler, and a second clamping ring are sequentially arranged in the center hole of the lead seat. The second clamping ring is clamped by a threaded clamping hollow plug.

[0007] Furthermore, multiple temperature measuring points of linear armored thermocouples are circumferentially distributed in the grooves of the inner walls of the first and second premixed channels. The heat-resistant thin pressure plate is spot-welded to the inner walls of the first and second air-fuel premixed channels and pressed tightly. The linear armored thermocouple and the nozzle are integrated into one structure. The lead diameter of the linear armored thermocouple is φ = 1~2mm.

[0008] A method for testing the backfire of a premixed hydrogen-blended natural gas fuel nozzle includes the following steps:

[0009] S1, enabling the premixed hydrogen-blended natural gas fuel nozzle to operate stably in the combustion chamber using pure natural gas fuel: According to the structure of the premixed hydrogen-blended natural gas fuel nozzle, on the inner wall of the first air-fuel premixing channel and the inner wall of the second air-fuel premixing channel, at a certain distance from the outlet end face, the circumferentially distributed temperature measuring points of the coupler wire are set. Pure natural gas fuel is used for ignition, and the main combustion air pressure, temperature and flow rate are adjusted to stable predetermined operating conditions and maintained in a stable combustion state;

[0010] S2, Measure the temperature at the thermocouple wire measuring point in the premixed channel under predetermined operating conditions using pure natural gas fuel to obtain the reference temperature: Based on step S1, after stable combustion for a certain period of time, the reference temperature T is obtained by measuring the inner wall temperature of the first and second premixed channels by the thermocouples at sections A and B, respectively. AS (The average of the measured values ​​at each measuring point) and T BS (The average value of each measuring point is taken);

[0011] S3, to enable the premixed hydrogen-blended natural gas fuel nozzle to operate stably in the combustion chamber using hydrogen-blended natural gas fuel: adjust the fuel to hydrogen-blended natural gas fuel, with a hydrogen volume ratio of K, so that the combustion chamber operates stably under the same conditions as in step S1, and maintains a stable combustion state.

[0012] S4, Measure the temperature at the thermocouple wire measuring point in the premixed channel under predetermined operating conditions of hydrogen-blended natural gas fuel to obtain the measured temperature: Under the predetermined stable combustion conditions in step S3, the measured values ​​of the inner wall temperatures of the first and second premixed channels, measured by thermocouples at sections A and B respectively, are T. fA (The average of the measured values ​​at each measuring point) and T fB (The average value of each measuring point is taken);

[0013] S5, performs logical judgment according to the set program: when under a certain stable operating condition T fA >T AS +△T or T fB >T BS If the temperature rise is +ΔT and the duration is t, then the premixed nozzle will experience backfire under this hydrogen blending ratio K condition; otherwise, backfire will not occur. Wherein ΔT is the allowable temperature rise determined based on the material and operating characteristics of the premixed hydrogen-blended natural gas fuel nozzle.

[0014] S6. If backfire occurs, record the hydrogen blending ratio K, shut off the fuel, and reduce the air parameters of the combustion chamber to the ignition condition. If backfire does not occur, adjust the hydrogen blending ratio in the natural gas to K1, and repeat steps S2 to S5 until backfire occurs.

[0015] S7. Adjust the test conditions and the hydrogen blending ratio of natural gas, repeat steps S1 to S6 and record the maximum hydrogen blending ratio for the corresponding conditions.

[0016] S8. Organize and record data to form a backfire characteristic curve under all operating conditions, and determine the maximum hydrogen blending ratio of natural gas under the condition that no backfire occurs in this premixed hydrogen-blended natural gas fuel nozzle.

[0017] Furthermore, in step S1, the distance between the measuring point section A in the first air-fuel premixing channel and the outlet end face is 5-8 mm, and the distance between the measuring point section B in the second air-fuel premixing channel and the outlet end face is 10-15 mm.

[0018] Furthermore, in step S5, the allowable temperature rise ΔT = 100℃ and the duration t ≥ 20s. Under different working conditions, ΔT and t can be taken with different values ​​depending on the material and working conditions.

[0019] Furthermore, in steps S5 and S6, the applicable range of hydrogen doping ratios K and K1 is 0-100%.

[0020] The beneficial effects of this invention are as follows:

[0021] 1. This invention provides a thermocouple lead hole on the mounting cover of the premixed hydrogen-blended natural gas fuel nozzle and fixes multiple thermocouple bundles on the nozzle body. All linear armored thermocouples and the nozzle are integrated into a single structure, which is convenient to disassemble and assemble, easy to maintain, highly practical for engineering and has good promotion potential.

[0022] 2. In this invention, the temperature measuring points of the linear armored thermocouple wire are evenly distributed circumferentially on the wall of the premixing channel, with 4 to 8 measuring points. This fully and accurately reflects the temperature changes in the premixing channel while ensuring minimal flow field interference. At the same time, the distance between the measuring point and the nozzle outlet section is reasonably designed to avoid misjudgment and backfire erosion, improve the accuracy of measurement results, and reduce test costs.

[0023] 3. The backfire temperature limit defined in this invention is the sum of the reference temperature Ts at a key location in the premixed channel when burning pure natural gas and the allowable temperature rise ΔT determined by the nozzle material and operating characteristics. This allows for timely and accurate judgment of backfire occurrence, providing a basis for the design and application of premixed hydrogen-blended natural gas fuel nozzles. At the same time, it quickly determines the upper limit of the hydrogen blending ratio and the backfire characteristics under all operating conditions of the nozzle structure, effectively maintaining the nozzle's working life, extending the gas turbine overhaul period, and providing technical support for the stable and safe operation of the gas turbine. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the premixed hydrogen-blended natural gas fuel nozzle structure of the present invention;

[0025] Figure 2 yes Figure 1 Sectional view of AA;

[0026] Figure 3 yes Figure 1 BB section view;

[0027] Figure 4 yes Figure 3 Enlarged view of part of the C-view;

[0028] Figure 5 This is a schematic diagram of the structure of the first and second clamping rings;

[0029] Figure 6 This is a schematic diagram of the test method of the present invention;

[0030] Figure 7 The test results of the example are the tempering characteristic curves.

[0031] In the diagram: 1: Nozzle body; 1-1: First fuel channel; 1-2: Second fuel channel; 1-3: First air cyclone; 1-4: Second air cyclone; 1-5: First fuel injection hole; 1-6: Second fuel injection hole; 1-7: First air-fuel premixing channel; 1-8: Second air-fuel premixing channel; 1-9: Inner wall of the first premixing channel; 1-10: Inner wall of the second premixing channel; 2: Mounting sealing cover; 2-1: Stepped lead wire hole; 3: Lead wire seat; 4-1: First clamping ring; 4-2: Second clamping ring; 5: Linear armored thermocouple; 5-1: Temperature measuring point of the thermocouple wire; 6: Sealing filler; 7: Compacting hollow plug; 8: High-temperature resistant thin pressure plate; 8-1: Spot weld point; 2001~2008: Steps S1~S8 Detailed Implementation

[0032] The present invention will now be further described with reference to the accompanying drawings.

[0033] like Figures 1-5 As shown, the premixed hydrogen-blended natural gas fuel nozzle used in this invention mainly includes a nozzle body 1, a linear armored thermocouple 5, and a high-temperature resistant thin-plate 8. Figure 1 , Figure 5 ), the inner wall of the first premixed channel 1-9 ( Figure 1 , Figure 2 ), the inner wall of the second premixed channel 1-10 ( Figure 1 , Figure 3 Install sealing cover 2, lead seat 3, tighten hollow plug 7, first clamping ring 4-1 ( Figure 1 , Figure 5 ), second clamping ring 4-2 ( Figure 1 , Figure 5 The nozzle body 1 is a two-stage radial premixing structure, including a first fuel channel 1-1, a first fuel injection hole 1-5, and a first air cyclone 1-3; a second fuel channel 1-2, a second fuel injection hole 1-6, and a second air cyclone 1-4. The first fuel injection hole 1-5 is located on the cyclone blades of the first air cyclone 1-3, and the second fuel injection hole 1-6 is located on the cyclone blades of the second air cyclone 1-4. Fuel enters through the fuel inlet and exits through multiple first fuel injection holes and second fuel injection holes. The second air cyclone 1-4 is arranged around the first air cyclone 1-3 to form a two-stage radial stage. A first air-fuel premixing channel 1-7 is located at the outlet of the two-stage air cyclone. Figure 1 , Figure 2 ) and second air-fuel premixing channels 1-8 ( Figure 1 , Figure 3 This allows the air and fuel involved in combustion to be spatially divided into two stages for uniform mixing, forming a premixed combustible that enters the combustion zone through the premixing channel. Figure 1The sealing cover 2 is a cover structure with a central hole, which is connected to the head of the nozzle body 1 by insertion and fasteners; the lead wire seat 3 is inserted into the circular stepped lead wire hole 2-1 on the sealing cover 2 and connected by welding. The first clamping ring 4-1, the sealing filler 6 and the second clamping ring 4-2 are sequentially arranged in the central hole of the lead wire seat 3, and the second clamping ring 4-2 is clamped by the clamping hollow plug 7 with thread connection, so that the sealing filler 6 fills the gap to ensure sealing; the multiple temperature measuring points 5-1 of the linear armored thermocouple 5 are evenly distributed circumferentially in the grooves of the inner wall 1-9 of the first premixing channel and the inner wall 1-10 of the second premixing channel. Figure 4 ), and is pressed and fixed by the corresponding heat-resistant thin pressure plate 8. Figure 4 The heat-resistant thin sheet 8 is welded to point 8-1. Figure 4 ) and compacted tightly against the inner walls 1-9 of the first air-fuel premixing channel and the inner walls 1-10 of the second air-fuel premixing channel. Figure 2 , Figure 3 Multiple linear armored thermocouples 5 have their wires led out through the flow gap between the swirling blades of the first air cyclone separator 1-3 and the second air cyclone separator 1-4. They are then bundled on the outer surface of the nozzle body 1 and fixed by spot welding with several heat-resistant thin pressure plates 8. Finally, they pass sequentially through the stepped lead hole 2-1 in the cover plate, the first clamping ring 4-1, the sealing filler 6, the second clamping ring 4-2, and the clamping hollow plug 7 before connecting to the temperature display device. Figure 1 (Only two wires are shown in the illustration) to complete signal transmission and temperature display.

[0034] like Figure 2 and Figure 3 As shown, the specific arrangement of the multiple linear armored thermocouples 5 is as follows: at a distance of d = 5~8mm from the outlet end face of the first premixing channel 1-7, at section AA ( Figure 1 The inner wall 1-9 of the first premixing channel has four temperature measuring points A1, A2, A3 and A4 arranged on its surface. Figure 2 At a distance of D = 10-15 mm from the outlet end face of the second premixing channel 1-8, at section BB ( Figure 1 The inner wall 1-10 of the second premixed channel has six temperature measuring points (B1, B2, B3, B4, B5, and B6) arranged on its surface. These points are circumferentially evenly distributed, allowing for comprehensive measurement of the actual temperature of the premixed channel's inner wall with minimal interference to the air-fuel mixture flow field. The distance from the end face is appropriate; too small a distance could easily lead to insufficient combustion in low-temperature combustion zones (such as...). Figure 1 (Illustration of the location area in the diagram) Temperature fluctuations caused by flame pulsation can lead to misjudgment. If the fluctuations are too large, the timing of backfire cannot be quickly and timely identified, resulting in nozzle erosion.

[0035] like Figure 4As shown, the temperature measuring point 5-1 of the linear armored thermocouple 5 is set in the rectangular groove of the inner wall 1-9 of the first premixing channel and the inner wall 1-10 of the second premixing channel. The cross-sectional area of ​​the groove is equivalent to the cross-sectional area of ​​the thermocouple wire. The temperature measuring point 5-1 of the thermocouple wire is pressed by the heat-resistant thin pressure plate 8 and fixed by the spot welding point 8-1 to ensure that the temperature measuring point of the thermocouple wire is in full contact with the premixing channel entity.

[0036] like Figure 5 As shown, the first clamping ring 4-1 and the second clamping ring 4-2 are circular disc structures with a central hole and a slit, with a thickness of δ = 1.5-2 mm. The slit width h is equivalent to the diameter of the thermocouple wire of the linear armored thermocouple 5, ensuring that a single thermocouple wire can smoothly enter the central hole. The equivalent area Sc of the central hole is equivalent to the sum of the cross-sectional areas of all linear armored thermocouples 5, which can fully ensure that all the thermocouple wires of the linear armored thermocouple 5 pass through the central hole while having the minimum flow area. In addition, the slits of the first clamping ring 4-1 and the second clamping ring 4-2 are staggered and not in the same plane, which facilitates the sealing of the filler 6.

[0037] Based on the above structure of the premixed hydrogen-blended natural gas fuel nozzle, this invention provides a method for testing the backfire of the premixed hydrogen-blended natural gas fuel nozzle, such as... Figure 6 As shown, it includes the following steps:

[0038] S1, enabling the premixed hydrogen-blended natural gas fuel nozzle to operate stably in the combustion chamber using pure natural gas fuel. 2001: According to the aforementioned premixed hydrogen-blended natural gas fuel nozzle structure, on the surfaces of the inner walls 1-9 of the first air-fuel premixing channel and the inner walls 1-10 of the second air-fuel premixing channel, at distances d and D from the outlet end face, uniformly arranged circumferential wire temperature measuring points are placed at sections A and B. Ignition is performed using pure natural gas fuel, and the main combustion air pressure, temperature, and flow rate are adjusted to a stable predetermined operating condition (e.g., ...). Figure 7 The value of 0.7 (in the operating condition) is maintained and a stable combustion state is maintained;

[0039] S2, Under pure natural gas fuel conditions, the temperature of the thermocouple wire measuring point in the premixed channel under predetermined operating conditions is measured to obtain the reference temperature 2002. Based on step S1, after stable combustion for a certain period of time, the reference inner wall temperatures of the first and second premixed channels are measured by thermocouples at sections A and B, respectively, to be T. AS (Temperature T) A1S Temperature T A2S Temperature T A3S Temperature T A4S (Average of 4 measurements) and T BS (Temperature T) B1S Temperature T B2S Temperature T B3S Temperature T B4S Temperature T B5STemperature T B6S (The average of the 6 measurements is taken.) Figure 7 The "reference temperature curve" shows a reference average temperature of approximately 400℃ under operating condition 0.7.

[0040] S3, make the premixed hydrogen-blended natural gas fuel nozzle work stably in the combustion chamber using hydrogen-blended natural gas fuel 2003: adjust the fuel to hydrogen-blended natural gas fuel, with a hydrogen volume ratio of K (e.g., 30%), so that the combustion chamber works stably under the same conditions as in step S1, and maintains a stable combustion state;

[0041] S4, Measure the temperature at the thermocouple wire measuring point in the premixed channel under the predetermined operating condition of hydrogen-blended natural gas fuel, and obtain the measured temperature 2004: Under the predetermined stable combustion condition in step S3, the measured values ​​of the inner wall temperatures of the first and second premixed channels, respectively, are obtained by thermocouples at sections A and B. fA (4-point average) and T fB (6-point average), such as Figure 7 The highest average temperature measured under the 0.7 operating condition, as shown in the "measured temperature curve", is approximately 430℃.

[0042] S5, perform logical judgment according to the set program 2005: when under a certain stable operating condition T fA >T AS +△T or T fB >T BS If the temperature rise is +ΔT and the duration is t, then the premixed nozzle experiences backfire under this hydrogen blending ratio K condition; otherwise, backfire does not occur. Here, ΔT is the allowable temperature rise determined based on the material and operating characteristics of the premixed hydrogen-blended natural gas fuel nozzle. Figure 7 As shown, since the highest measured average temperature is 430℃≤(400℃+100℃), the logical judgment result shows that no tempering occurred.

[0043] S6, if backfire occurs, record the hydrogen blending ratio K, shut off the fuel, and reduce the combustion chamber operating air parameters to ignition conditions. If backfire does not occur, adjust the hydrogen blending ratio in the natural gas to K1, and repeat steps S2 to S5 until backfire occurs. Figure 7 As shown, after multiple adjustments to the hydrogen doping ratio, when the hydrogen doping ratio was adjusted to K1 = 51%, the highest measured average temperature T was [value missing]. fA or T fB If the temperature exceeds (400℃+100℃) and the duration is at least 20 seconds, then the logic determines that backfire has occurred, and the test result under the 0.7 operating condition is that the maximum natural gas hydrogen blending ratio is 51%.

[0044] S7, adjust the test conditions and the hydrogen blending ratio of natural gas, repeat steps S1 to S6 and record the maximum hydrogen blending ratio of the corresponding conditions 2007.

[0045] S8, organize and record data to form tempering characteristic curves under all operating conditions (e.g., Figure 7 As shown), the maximum hydrogen blending ratio of natural gas under the condition that no backfire occurs in this premixed hydrogen-blended natural gas fuel nozzle is determined to be 2008.

[0046] In step S1, the number of temperature measuring points arranged on the inner walls 1-9 of the first air-fuel premixing channel and the inner walls 1-10 of the second air-fuel premixing channel is 4 to 8 points, evenly distributed circumferentially. This ensures that the temperature changes in the premixing channel are fully and accurately reflected while minimizing flow field interference. The distance d from the measuring point A on the inner wall 1-9 of the first air-fuel premixing channel to the outlet end face is 5 to 8 mm, and the distance D from the measuring point B on the inner wall 1-10 of the second air-fuel premixing channel to the outlet end face is 10 to 15 mm. If the distance is too small, it is easy to cause misjudgment due to temperature fluctuations caused by low-temperature flame pulsation. If the distance is too large, it is impossible to quickly and timely identify the timing of backfire and erode the nozzle.

[0047] In step S5, the allowable temperature rise ΔT = 100℃ and the duration t ≥ 20s. Under different working conditions, ΔT and t can be taken with different values ​​depending on the material and working conditions.

[0048] In step S6, the applicable range of the hydrogen doping ratios K and K1 is 0-100%.

[0049] The linear armored thermocouple lead holder 3 is mounted on the mounting sealing cover plate 2, realizing an integrated structure of thermocouple lead and nozzle. The nozzle is easy to disassemble and assemble, while ensuring good nozzle installation sealing, suitable for full pressure and high pressure tests. The diameter of the linear armored thermocouple 5 wire is φ = 1~2mm. The resistance of the linear armored thermocouple 5 wire is measured before welding, after welding, before nozzle installation, and after installation. The values ​​should be basically close to prevent damage to the wire caused by improper operation.

[0050] This invention is defined as a "tempering test method". Similar terms such as "tempering test method", "tempering detection method", "tempering development method", and "tempering research method" are all within the scope of protection of this patent if they have the same substantive intent as this invention.

[0051] This invention defines the temperature limit for flashback as the reference temperature TS+ΔT at a key location within the premixed channel during natural gas combustion. This allows for timely and accurate detection of flashback, providing a basis for the design and application of hydrogen-blended premixed nozzles for natural gas. It quickly determines the upper limit of hydrogen blending and flashback characteristics in the current nozzle structure, effectively maintaining nozzle lifespan and extending gas turbine overhaul periods. Furthermore, this invention offers rapid and accurate verification results, low testing costs, strong engineering applicability and broad applicability. Its comprehensive and effective assessment of flashback characteristics can reduce the development cost of low-emission hydrogen fuel combustors, shorten the development cycle, and increase the success rate, thus providing technical support for the stable and safe operation of gas turbines. This invention is applicable to flashback testing and improved design of combustors with air-fuel premixed structures in the field of gas turbines.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for testing the flashback of a premixed hydrogen-blended natural gas fuel nozzle, characterized in that, Includes the following steps: S1 enables the premixed hydrogen-blended natural gas fuel nozzle to operate stably in the combustion chamber using pure natural gas fuel. The premixed hydrogen-blended natural gas fuel nozzle structure includes: a nozzle body; the nozzle body is a two-stage radial premixing structure, including a first fuel channel, a first fuel injection orifice, a first air cyclone, a second fuel channel, a second fuel injection orifice, and a second air cyclone; the first fuel injection orifice is disposed on the cyclone blades of the first air cyclone, and the second fuel injection orifice is disposed on the cyclone blades of the second air cyclone; one end of the first fuel channel and the second fuel channel is connected to the fuel inlet. The other end is connected to the first fuel injection hole and the second fuel injection hole respectively; the second air cyclone is arranged around the first air cyclone to form two-stage radial stages, and a first air-fuel premixing channel and a second air-fuel premixing channel are set at the outlet of the two-stage air cyclone; on the inner wall of the first air-fuel premixing channel and the inner wall surface of the second air-fuel premixing channel, at a certain distance from the outlet end face, the circumferentially distributed filament temperature measuring points are set. Pure natural gas fuel is used for ignition, and the main combustion air pressure, temperature and flow rate are adjusted to stable predetermined operating conditions and maintained in a stable combustion state; S2, measure the temperature of the odd filament point in the premixing channel under the condition of pure natural gas fuel and the predetermined working condition to obtain the reference temperature: on the basis of step S1, after a certain time of stable combustion, the thermal electric couple in the cross section A and cross section B respectively measures the reference temperature of the inner wall of the first air-fuel premixing channel and the second air-fuel premixing channel as T AS and T BS， T AS and T BS The measured values of each point are averaged; S3, to enable the premixed hydrogen-blended natural gas fuel nozzle to operate stably in the combustion chamber using hydrogen-blended natural gas fuel: adjust the fuel to hydrogen-blended natural gas fuel, with a hydrogen volume ratio of K, so that the combustion chamber operates stably under the same conditions as in step S1, and maintains a stable combustion state. S4, Measure the temperature at the thermocouple wire measuring point in the premixed channel under predetermined operating conditions for hydrogen-blended natural gas fuel, and obtain the measured temperature: Under the predetermined stable combustion conditions in step S3, the measured values ​​of the inner wall temperatures of the first air-fuel premixed channel and the second air-fuel premixed channel, respectively, are T by thermocouples at sections A and B. fA and T fB T fA and T fB The average value of the measurements at each measuring point is taken. S5, performs logical judgment according to the set program: when under a certain stable operating condition T fA >T AS +△T or T fB >T BS If the temperature rise is +ΔT and the duration is t, then the premixed nozzle will experience backfire under this hydrogen blending ratio K condition; otherwise, backfire will not occur. Wherein ΔT is the allowable temperature rise determined based on the material and operating characteristics of the premixed hydrogen-blended natural gas fuel nozzle. S6. If backfire occurs, record the hydrogen blending ratio K, shut off the fuel, and reduce the air parameters of the combustion chamber to the ignition condition. If backfire does not occur, adjust the hydrogen blending ratio in the natural gas to K1, and repeat steps S2 to S5 until backfire occurs. S7. Adjust the test conditions and the hydrogen blending ratio of natural gas, repeat steps S1 to S6 and record the maximum hydrogen blending ratio for the corresponding conditions. S8. Organize and record data to form a backfire characteristic curve under all operating conditions, and determine the maximum hydrogen blending ratio of natural gas under the condition that no backfire occurs in this premixed hydrogen-blended natural gas fuel nozzle.

2. The method for testing the flashback of a premixed hydrogen-blended natural gas fuel nozzle according to claim 1, characterized in that, In step S1, the distance between the measuring point section A in the first air-fuel premixing channel and the outlet end face is 5-8 mm, and the distance between the measuring point section B in the second air-fuel premixing channel and the outlet end face is 10-15 mm.

3. The method for testing the flashback of a premixed hydrogen-blended natural gas fuel nozzle according to claim 1, characterized in that, In step S5, the allowable temperature rise ΔT = 100℃ and the duration t ≥ 20s.

4. The method for testing the flashback of a premixed hydrogen-blended natural gas fuel nozzle according to claim 1, characterized in that, In steps S5 and S6, the applicable range of hydrogen doping ratios K and K1 is 0-100%.

5. The method for testing the flashback of a premixed hydrogen-blended natural gas fuel nozzle according to claim 1, characterized in that, The head of the nozzle body is connected to the mounting sealing cover plate by fasteners after insertion; the mounting sealing cover plate is a cover plate structure with a central hole.

6. The method for testing the flashback of a premixed hydrogen-blended natural gas fuel nozzle according to claim 5, characterized in that, The circular stepped hole for installing the sealing cover plate is inserted into the lead seat. The center hole is sequentially provided with a first compression ring, a sealing filler, and a second compression ring. The second compression ring is compressed by a threaded compression hollow plug.

7. The method for testing the flashback of a premixed hydrogen-blended natural gas fuel nozzle according to claim 1, characterized in that, Multiple temperature measuring points of linear armored thermocouples are circumferentially distributed in the grooves of the inner walls of the first and second air-fuel premixing channels. The heat-resistant thin pressure plate is spot-welded to the inner walls of the first and second air-fuel premixing channels and pressed tightly. The linear armored thermocouple and the nozzle are integrated into one structure. The lead diameter of the linear armored thermocouple is φ=1~2mm.

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