Method of operating a low-total-temperature state of a hot-jet test apparatus for a shock tunnel

Abstract

The application provides a working method of a low total temperature state of a hot jet experiment device of a shock wave wind tunnel, which utilizes the principles of stable combustion limit, ignition limit and high temperature ablation limit in a combustion process to determine the optimal ignition area of the equivalence ratio of hydrogen and air combustion; in combination with the operation time sequence of the hot jet experiment device, the equivalence ratio of hydrogen and air combustion is ignited under the working condition of the optimal ignition area, and the combustion chamber stably combusts under a high total temperature state; by reducing the equivalence ratio of hydrogen and air combustion within the lean oil ignition area range, the combustion chamber continues to stably combust under a low total temperature state. The hydrogen and air in the combustion chamber are ignited under the working condition of a large equivalence ratio and stably combust under a high total temperature state, then the flow of hydrogen and air is accurately adjusted to the working condition of a small equivalence ratio by an electronic pressure reducing valve, and the stable combustion under a low total temperature state is maintained, thereby solving the problem that the hot jet experiment device cannot work under a low total temperature state.

Description

Technical Field

[0001] This invention relates to the field of shock tunnels, specifically to a method for operating a thermal jet experimental device in a low total temperature state. It employs a hydrogen-air mixed combustion method and utilizes the principles of stable combustion limit, ignition limit, and high-temperature ablation limit during the combustion process, combined with the operating sequence, to solve the problem that the thermal jet experimental device cannot operate under low total temperature conditions. Background Technology

[0002] During hypersonic vehicle flight, the coupling of internal and external airflows within the engine, as well as the jet stream generated for attitude and trajectory control, produce large-area unsteady and unstable flow fields, including strong shock waves / shock wave interference, shock wave / boundary layer interference, and separation / reattachment. These significantly disrupt the aerodynamics and aerothermal properties of the vehicle. Aerothermal ground tests are primarily conducted in shock tunnels operating on the millisecond scale. The generation of transiently stable hot jet stream sources, millisecond-level timing synchronization, and the creation of small-scale models present significant challenges to shock tunnel hot jet stream experiments. Therefore, we propose a novel shock tunnel hot jet stream experimental setup and method (Application No.: 202110529968.3 Hot Jet Stream Experimental Setup for Shock Tunnel, Application No.: 202110529954.1 Hot Jet Stream Experimental Method for Shock Tunnel). This hot jet stream experimental setup utilizes a combined hydrogen and air combustion process to achieve supersonic gas ejection from the wind tunnel model. The integrated thermal jet experimental device fully considers safety, reliability, stability, and future scalability.

[0003] For this thermal jet experimental device, to ensure a safe and smooth experimental process (no explosion, no flameout, no pulse vibration), the following three factors need to be considered comprehensively:

[0004] 1. Stable ignition in the combustion chamber;

[0005] 2. Stable combustion occurs inside the combustion chamber after ignition;

[0006] 3. Ensure that the combustion chamber is not burned during the ignition and combustion process.

[0007] Multiple tests revealed that the thermal jet experimental device can only operate within an equivalence ratio range of (f2, f3). Below an equivalence ratio of f2, the flame cannot be ignited. Therefore, the limiting temperature range of the device is (898K, 1427K). Obtaining jet gas at even lower temperatures using this device is extremely difficult. However, in practical experiments, there is a significant need to generate hot gas jets at 650K, highlighting the problem of the thermal jet experimental device failing to ignite and start operating at low total temperatures. Summary of the Invention

[0008] To address the aforementioned issues, this invention provides a method for operating a thermal jet experimental device in a low total temperature state. It employs a hydrogen-air mixed combustion method, utilizing the principles of stable combustion limit, ignition limit, and high-temperature ablation limit during combustion, combined with the operating sequence, to solve the problem that the thermal jet experimental device cannot operate in a low total temperature state.

[0009] A method for operating a thermal jet experimental device in a shock tunnel under low total temperature conditions includes:

[0010] 1) Utilizing the principles of stable combustion limit, ignition limit, and high-temperature ablation limit during the combustion process, determine the optimal ignition region for the hydrogen-air combustion equivalence ratio. The equivalence ratio refers to the ratio of the amount of air theoretically required for complete combustion to the amount of air actually supplied during fuel combustion.

[0011] 2) By controlling the flow rate of hydrogen and air entering the combustion chamber, the hydrogen and air combustion equivalence ratio is adjusted to ignite under the optimal ignition zone conditions, and the combustion chamber is stably combusted at a high total temperature.

[0012] 3) By precisely adjusting the flow rates of hydrogen and air through electronic pressure reducing valves, the hydrogen-to-air combustion equivalence ratio is reduced within the lean ignition zone, causing the total temperature of the combustion chamber to decrease, thus enabling stable combustion to continue in the combustion chamber at a low total temperature.

[0013] As a preferred technical solution of the present invention, the optimal ignition region in step 1) is the lean oil ignition region excluding the high-temperature ablation region, which is between the lean oil flame stabilization limit and the lean oil high temperature limit. Preferably, it is the ignition region between the lean oil ignition limit and the lean oil high temperature limit.

[0014] As a preferred technical solution of the present invention, in step 3), the reduction of the hydrogen and air combustion equivalence ratio is specifically within the flame stability region between the lean flame stabilization limit and the lean ignition limit.

[0015] As a preferred embodiment of the present invention, the working method further includes:

[0016] Before step 2), first open the air solenoid shut-off valve to supply air to the combustion chamber, then turn on the spark plug for continuous pulse ignition and open the hydrogen valve.

[0017] As a preferred embodiment of the present invention, the working method further includes:

[0018] After step 2), the hydrogen and air are in a stable combustion condition, so turn off the spark plug.

[0019] As a preferred embodiment of the present invention, the working method further includes:

[0020] The shutdown process of the thermal jet experimental device is as follows: First, close the hydrogen solenoid shut-off valve to cut off the hydrogen supply. After the hydrogen flow rate becomes 0 and the flame in the combustion chamber is extinguished, close the air solenoid shut-off valve to cut off the air supply, and the air flow rate becomes 0. Then, close all the shut-off valves on the hydrogen and air pipelines, the industrial control computer stops control, and the experiment ends.

[0021] As a preferred technical solution of the present invention, in the working method, preferably, the lean oil flame stabilization limit is 0.09, the lean oil ignition limit is 0.19, and the lean oil high temperature limit is 0.4.

[0022] As a preferred embodiment of the present invention, the working method involves unequal pauses between each step before proceeding to the next step.

[0023] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a working method for a thermal jet experimental device in a shock tunnel under low total temperature conditions. Combining the principles of stable combustion limit, ignition limit and high temperature ablation limit in the combustion process, the present invention controls the equivalence ratio of hydrogen and air combustion, so that the hydrogen and air in the combustion chamber are first ignited under a high equivalence ratio condition and stably burned under a high total temperature condition. Then, the flow rates of hydrogen and air are precisely adjusted to a low equivalence ratio condition by electronic pressure reducing valves, so as to maintain stable combustion under low total temperature conditions. This solves the problem that the thermal jet experimental device cannot work under low total temperature conditions. Attached Figure Description

[0024] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the thermal jet experimental device in this invention;

[0026] Figure 2 This is an explanatory diagram of the hydrogen-air ignition limit and flame stability limit in this invention;

[0027] Figure 3 This is a schematic diagram of the startup sequence of the thermal jet experimental device under low total temperature conditions in this invention;

[0028] The markings in the image are as follows:

[0029] 1. Hydrogen cylinder assembly 2. Hydrogen filter

[0030] 3. Hydrogen cylinder pressure gauge; 4. Hydrogen manual shut-off valve

[0031] 5. Hydrogen exhaust shut-off valve; 6. Hydrogen electronic pressure reducing valve

[0032] 7. Pressure sensor after hydrogen pressure reducing valve; 8. Hydrogen solenoid shut-off valve

[0033] 9. Hydrogen check valve 10. Hydrogen supply pressure sensor

[0034] 11. Hydrogen supply temperature sensor 12. Hydrogen flow meter

[0035] 13. Hydrogen pipeline 14. Air cylinder

[0036] 15. Air filter 16. Air cylinder pressure gauge

[0037] 17. Air exhaust shut-off valve 18. Manual air shut-off valve

[0038] 19. Air electronic pressure reducing valve; 20. Pressure sensor after air pressure reducing valve.

[0039] 21. Air solenoid shut-off valve 22. Air check valve

[0040] 23. Air supply temperature sensor 24. Air supply temperature sensor

[0041] 25. Air flow meter; 26. Air duct;

[0042] 27. Spark plug 28. Combustion chamber pressure sensor

[0043] 29. Combustion chamber temperature sensor 30. Combustion chamber

[0044] 31. Laval nozzle 32. Aircraft model

[0045] 33. Thermal jet airflow 34. Shock tube

[0046] 35. Wind tunnel nozzle 36. Wind tunnel test chamber

[0047] 37. Wind tunnel airflow 38. Analog output signal

[0048] 39. Analog input signal 40. Digital output signal

[0049] 41. Analog output signal isolation module 42. Analog input signal isolation module

[0050] 43. Digital output signal isolation module; 44. Data control and acquisition card

[0051] 45. Industrial control computer. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] like Figure 1 The diagram shown is a schematic of the thermal jet experimental apparatus. The characteristics of its components are as follows:

[0054] Hydrogen cylinder group 1 is used to provide hydrogen gas source, usually using 1-2 40L hydrogen steel cylinders.

[0055] Hydrogen filter 2 is used to protect components such as shut-off valves and pressure reducing valves on pipelines, preventing impurities in the gas from entering the valves and damaging them.

[0056] Hydrogen cylinder pressure gauge 3 is used to measure the hydrogen pressure in the hydrogen cylinder.

[0057] Hydrogen manual shut-off valve 4 is the main valve for hydrogen, used to open or close the hydrogen supply.

[0058] Hydrogen exhaust shut-off valve 5 is used to open after all other valves are closed to release the remaining gas in the pipeline.

[0059] The hydrogen electronic pressure reducing valve 6 is used to reduce the high pressure of the gas cylinder to a set pressure. This valve is connected to a computer data acquisition card, and can be controlled by computer commands to adjust the output pressure as needed.

[0060] The pressure sensor 7 after the hydrogen pressure reducing valve is used to measure the pressure after the electronic pressure reducing valve. This sensor is connected to the data acquisition card via a signal line, and the pressure value can be read in the computer.

[0061] Hydrogen electromagnetic shut-off valve 8 is connected to a computer acquisition card for precise computer control of the valve's opening and closing, ensuring ignition timing and preventing explosions. The use of electrical signals to remotely control the valve also avoids the dangers of manual operation during the experiment.

[0062] The hydrogen check valve 9 prevents the gas flow in the combustion chamber from flowing back into the hydrogen pipeline, which could potentially cause a combustion explosion inside the hydrogen pipeline.

[0063] Hydrogen supply pressure sensor 10 is used to measure the total hydrogen pressure before the hydrogen flow meter.

[0064] Hydrogen supply temperature sensor 11 is used to measure the total temperature of hydrogen before the hydrogen flow meter.

[0065] Hydrogen flow meter 12 is a sonic nozzle flow meter. This flow meter can measure the hydrogen flow rate while simultaneously controlling the flow rate stably, preventing downstream combustion chamber pressure changes from affecting the hydrogen flow rate. Specific flow measurement and control methods will be discussed later.

[0066] Hydrogen pipeline 13 includes pipes connecting each valve and sensor from the hydrogen cylinder. This pipeline is a high-pressure pipeline and is made of stainless steel pressure-resistant pipe. The pipe diameter is designed according to the pressure pipeline requirements. Here, a φ12×1.5 specification pipe with an outer diameter of 12mm and a wall thickness of 1.5mm is used.

[0067] Air cylinder 14 is used to provide air source, usually using 4 40L air cylinders.

[0068] Air filter 15 is used to protect parts such as shut-off valves and pressure reducing valves on pipelines, preventing impurities in the gas from entering the valves and damaging them.

[0069] Air cylinder pressure gauge 16 is used to measure the air pressure in an air cylinder.

[0070] Air exhaust shut-off valve 17 is used to open after all other valves are closed to release the remaining gas in the pipeline.

[0071] Air manual shut-off valve 18 is the main air valve, used to open or shut off the air supply.

[0072] The electronic air pressure reducing valve 19 is used to reduce the high pressure of the gas cylinder to a set pressure. This valve is connected to a computer data acquisition card, and can be controlled by the computer to adjust the output pressure as required.

[0073] The pressure sensor 20 after the air pressure reducing valve is used to measure the pressure after the electronic pressure reducing valve. The sensor is connected to the data acquisition card via a signal line, and the pressure value can be read in the computer.

[0074] Air electromagnetic shut-off valve 21, connected to a computer acquisition card, is used for precise computer control of the valve's opening and closing to ensure ignition timing and prevent explosions. Remote control of the valve via electrical signals also avoids the dangers of manual operation during experiments.

[0075] Air check valve 22 prevents airflow from the combustion chamber from returning to the air duct.

[0076] Air supply temperature sensor 23 is used to measure the total hydrogen pressure before the air flow meter.

[0077] Air supply temperature sensor 24 is used to measure the total temperature of hydrogen gas before the air flow meter.

[0078] Air flow meter 25 is a sonic nozzle flow meter. This flow meter can measure air flow while simultaneously controlling the flow rate, preventing downstream combustion chamber pressure changes from affecting the air flow. Specific flow measurement and control methods will be discussed later.

[0079] Air duct 26, including the pipes connecting each valve and sensor from the hydrogen cylinder, is a high-pressure pipe made of stainless steel pressure-resistant tubing. The pipe diameter is designed according to the pressure pipeline requirements; here, a φ20×2 specification pipe with an outer diameter of 20mm and a wall thickness of 2mm is used.

[0080] Spark plug 27 can generate a high-frequency electric spark for ignition of hydrogen and air mixtures. The spark plug is remotely controlled by a computer.

[0081] Combustion chamber pressure sensor 28 is used to measure the gas pressure inside the combustion chamber.

[0082] Combustion chamber temperature sensor 29 is used to measure the temperature of the gas inside the combustion chamber.

[0083] Combustion chamber 30 is used for the mixing and ignition of hydrogen and air to produce high-temperature and high-pressure gas.

[0084] The Laval nozzle 31 is used to accelerate high-temperature, high-pressure gas to supersonic speeds.

[0085] The aircraft model 32 can have a triangular layout like an airplane or a cylindrical layout like a missile, with the combustion chamber and nozzle for the hot jet installed inside the aircraft.

[0086] The hot jet stream 33 is accelerated to supersonic speed through the Laval nozzle and is discharged from the tail of the model into the shock tunnel test chamber.

[0087] Shock tube 34, the shock tube of the shock tunnel experimental platform, is used to generate high-temperature and high-pressure airflow and shock waves.

[0088] The wind tunnel nozzle 35 is used to accelerate the airflow in the shock tube to supersonic speed. The airflow is then injected into the wind tunnel test chamber and blows air onto the aircraft model.

[0089] Wind tunnel test chamber 36 is used to place aircraft models and study the stress and heat conditions of the models in the shock wave wind tunnel flow field.

[0090] Wind tunnel airflow 37 is generated by high-temperature, high-pressure gas in the shock tube after being accelerated through the nozzle, and acts on the aircraft model.

[0091] The analog output signal 38 is calculated and controlled by the acquisition card to output a 0-10V analog signal to control the electronic pressure reducing valve, so that the gas pressure after the valve is reduced to the set pressure value.

[0092] The specific working principle and related experimental methods of this thermal jet experimental device have been disclosed in the patent applications (Application No.: 202110529968.3 - Thermal Jet Experimental Device for Shock Tunnel, Application No.: 202110529954.1 - Thermal Jet Experimental Method for Shock Tunnel), and will not be elaborated in this invention.

[0093] Due to the different ignition limits and flame stabilization limits of the combustion of different fuels and oxidants, the limit region of gaseous fuels will be larger than that of liquid fuels, and different gas species will also result in different regions. For example Figure 2 The figure shows the illustration of the ignition limit and flame stabilization limit of hydrogen - air. The abscissa is the equivalence ratio f of the combustion of hydrogen and air. The equivalence ratio refers to the ratio of the amount of air required for complete combustion in theory to the actual supplied air amount during fuel combustion, and it is a dimensionless number. When the equivalence ratio is greater than 1, it means that the actual air amount contained in the combustible mixture is less than the required theoretical air amount, that is, the air amount is insufficient. On the contrary, when the equivalence ratio is less than 1, it means that the actual air amount contained in the combustible mixture exceeds the required theoretical air amount, that is, the air amount is excessive. The ordinate is the ignition delay time t. The ignition delay time is the time required for the mixture of hydrogen and air to react under a certain temperature and pressure. The shorter the delay time, the easier it is to ignite or stabilize the flame. When the delay time is greater than a certain value, the flame cannot be ignited or stabilized. The delay time t and the equivalence ratio f are important physical properties parameters in the design of the combustion chamber. Since different combustion chambers and injectors have different ignition delay times and equivalence ratios, but the rules are basically the same (for example, within a suitable range of equivalence ratios, the ignition delay time is very short, while when the equivalence ratio is particularly small or particularly large, the ignition delay time is particularly long), specific numerical values of the ignition delay time and the equivalence ratio will not be given here, but a qualitative image is used to illustrate the regular relationship.

[0094] For each corresponding combustion chamber and the hydrogen - air combination, there is a critical time tc. When the time is greater than tc, hydrogen cannot be ignited, and when the time is less than or equal to tc, normal ignition occurs.

[0095] Figure 2 The thick solid - line - drawn parabola in is the flame stabilization limit curve, and the thin dashed - line parabola is the ignition limit curve. There are 7 key points on the curve. Point f1 is the lean - fuel flame stabilization limit, point f2 is the lean - fuel ignition limit, point f3 is the lean - fuel high - temperature limit, point f = 1 is the stoichiometric equivalence ratio point, point f4 is the rich - fuel high - temperature limit, point f5 is the rich - fuel ignition limit, point f6 is the rich - fuel flame stabilization limit. These 7 points form 6 working regions, namely:

[0096] (1) Lean - fuel extinction region, f < f1. In this region, the flow rate of hydrogen is much smaller than that of air, and no matter what method is adopted and how much ignition energy is used, ignition cannot be successful.

[0097] (2) Flame stability region, f1 < f < f6. In this region, as long as hydrogen and air are continuously and stably supplied, the flame can remain stable and not go out;

[0098] (3) Ignition region, f2 < f < f5. In this region, hydrogen can be ignited by a small-energy electric spark or heat source;

[0099] (4) High-temperature ablation region, f3 < f < f4. This is a region with a very high flame temperature, usually above 2000K. Conventional engine manufacturing metals cannot withstand it, and ablation may occur. At this time, the engine design needs to consider wall thermal protection to prevent high-temperature ablation. Therefore, the corresponding region is the high-temperature ablation region;

[0100] (5) Appropriate equivalence ratio point, f = 1. At this time, hydrogen and air completely undergo chemical reaction combustion, and the products are water, nitrogen, etc.;

[0101] (6) Rich fuel extinction region, f > f6. In this region, the flow rate of hydrogen is very large and the flow rate of air is small. No matter what method is used and how much ignition energy is applied, ignition cannot be successful.

[0102] Based on the above results, it can be obtained that: the flame stability limit of combustion is greater than the ignition limit, and the ignition region is within the flame stability region. That is, hydrogen is not easy to be ignited, but once ignited, the flame is easy to be stable and continuous.

[0103] The selection of the ignition region of the thermal jet experimental device is introduced in detail below:

[0104] During the ignition start-up process of the combustion chamber, since the cooling flow field has not been fully established and the cooling capacity is poor, the ignition state point should avoid the high-temperature ablation region f3 < f < f4. The only available ignition regions left are Figure 2 the left f1 < f < f3 and the right f4 < f < f6 regions in

[0105] In these two regions, since the hydrogen content in the right f4 < f < f6 region is large, there is still a certain amount of unburned hydrogen in the combustion chamber. These hydrogen will be injected into the shock tunnel and are prone to explosion hazards. Therefore, when igniting hydrogen and air, the equivalence ratio should be designed in the left f1 < f < f3 region. At this time, the amount of hydrogen is small and it burns completely. There is only air and water in the product gas, without hydrogen residue, and no explosion hazard will occur. The best ignition region is as shown in Figure 2 the annotation in

[0106] According to the above theoretical analysis, after comprehensively considering the ignition limit, high-temperature ablation, and tail gas residue factors, the ignition state point of the thermal jet experiment device should be selected within the lean fuel ignition range on the left side excluding the high-temperature ablation area, that is, the area where f1 < f < f3.

[0107] However, the conclusion on the selection area of the ignition state point of the thermal jet experiment device obtained above is only based on theoretical analysis. Through experiments, it is found that the thermal jet experiment device can only operate within the equivalence ratio range of (f2, f3). When the equivalence ratio is lower than f2, the flame cannot be ignited. Therefore, the limit temperature range of the device is (898K, 1427K). In actual work, there is a large demand to operate at a temperature of 650K to generate a hot gas jet. Therefore, to overcome this difficulty, through design and continuous experiments, the present invention has invented a working method for the low total temperature state of a thermal jet experiment device for a shock tunnel. The following is the experimental test process:

[0108] To give the working state range of the thermal jet experiment device, ignition and stable combustion tests are carried out on the combustion chamber at different equivalence ratios f. According to the previous analysis and combined with Figure 2 , when the equivalence ratio is greater than 1, there are risks of high-temperature ablation and hydrogen residue explosion. In an actual shock tunnel, it is not necessary for the combustion chamber to operate in this area. Therefore, there is no need to test the area where the equivalence ratio is greater than 1, and only the working area where the equivalence ratio is less than 1 is tested. Finally, three points of the lean fuel flame stabilization limit f1 = 0.09, the lean fuel ignition limit f2 = 0.19, and the lean fuel high-temperature limit f3 = 0.40 are obtained. The following table shows the actual values and working condition points of different equivalence ratios.

[0109] Table 1 Three key working state points of the thermal jet experiment device

[0110]

[0111] The oxygen-to-fuel ratio is the mass ratio of air to hydrogen, and there is a certain conversion relationship between it and the equivalence ratio f. Generally speaking, the smaller the equivalence ratio, the larger the oxygen-to-fuel ratio, and the larger the equivalence ratio, the smaller the oxygen-to-fuel ratio. According to the above analysis and combined with the test results in the above table, the working conditions of the combustion chamber are mainly in the following areas:

[0112] (a) f < 0.09, this area belongs to the lean fuel extinction area, and the combustion chamber cannot be ignited, that is, the thermal jet experiment device generates a gas flow with a total temperature less than 600K;

[0113] (b) 0.09 ≤ f < 0.19, in this area (the flame stabilization area between the lean fuel flame stabilization limit and the lean fuel ignition limit), the hydrogen-air in the combustion chamber cannot be ignited but can burn stably, and the total temperature of the combustion chamber is within the range of 600K to 898K;

[0114] (c) 0.19≤f<0.4, in this region (the ignition region between the lean oil ignition limit and the lean oil high temperature limit), the combustion chamber can ignite and burn stably without ablation, and the total temperature of the combustion chamber is in the range of 898K~1427K;

[0115] (d)f≥0.4, this area belongs to the high temperature ablation zone, the total temperature of the combustion chamber exceeds 1427K, and the combustion chamber will begin to show ablation damage.

[0116] In summary, the thermal jet experimental device could not operate in regions a and d, could operate stably and normally in region c, and could burn stably in region b, but could not start up smoothly.

[0117] Based on the above, the present invention provides a method for operating a thermal jet experimental device for a shock tunnel under low total temperature conditions, comprising the following steps:

[0118] 1) Utilizing the principles of stable combustion limit, ignition limit, and high-temperature ablation limit during the combustion process, determine the optimal ignition region for the hydrogen and air combustion equivalence ratio. The optimal ignition region is the lean ignition region excluding the high-temperature ablation region, which is between the lean flame stability limit and the lean high temperature limit. The preferred ignition region is the region between the lean ignition limit and the lean high temperature limit, i.e. region c.

[0119] 2) By controlling the flow rate of hydrogen and air entering the combustion chamber 30, the hydrogen and air combustion equivalence ratio is adjusted to ignite under the condition of optimal ignition zone, and the combustion chamber 30 is stably combusted under high total temperature.

[0120] 3) By precisely adjusting the flow rates of hydrogen and air through electronic pressure reducing valves, the hydrogen-to-air combustion equivalence ratio is reduced within the lean ignition zone (preferably specifically reduced to the flame stability zone between the lean flame stabilization limit and the lean ignition limit, i.e., zone b). The total temperature of the combustion chamber 30 begins to decrease, allowing the combustion chamber 30 to continue stable combustion at a low total temperature.

[0121] This method first utilizes a spark plug as ignition energy to ignite and burn hydrogen and air within the equivalence ratio (f2, f3). Then, the spark plug is turned off; at this point, hydrogen and air can still maintain stable combustion, and the flame persists. Further reducing the hydrogen flow rate or increasing the air flow rate lowers the equivalence ratio, and the flame still maintains stable combustion. Experiments show that when the equivalence ratio falls below f1, the flame extinguishes and unstable combustion fails, corresponding to a total gas temperature of 600K. The equivalence ratio decreases within 1-10 seconds, preferably 2 seconds. Therefore, by adopting this method, the operating range of the jet device can be expanded from the original (f2, f3) to (f1, f3), reducing the minimum total operating temperature of the device from 898K to 600K, significantly and effectively increasing the operating range and meeting the 650K operating point requirement.

[0122] Figure 3 The diagram shows the startup sequence of the thermal jet experimental device under low total temperature conditions. The horizontal axis represents time, and the vertical axis represents the operating condition. However, due to differences in the design of the combustion chamber and injector in actual thermal jet experimental devices, the operating time and condition points are not entirely the same. Therefore, the diagram does not provide precise time and condition points, but only provides qualitative descriptions based on experimental patterns. Based on the above working method, the operating sequence for the thermal jet experimental device used in the shock tunnel under low total temperature conditions is as follows:

[0123] 1. At time t0, the experiment begins. The pressures of the hydrogen electronic pressure reducing valve 6 and the air electronic pressure reducing valve 19 are input into the industrial control computer 45, so that the equivalence ratio of hydrogen to air is in the stable combustion region c. At this time, the flow rates of hydrogen and air in the combustion chamber are both 0.

[0124] 2. At time t1, the air solenoid shut-off valve 21 is opened to supply air to the combustion chamber.

[0125] 3. At time t2, the spark plug is opened for continuous pulse ignition. If hydrogen enters the combustion chamber before the spark plug ignition time, it will accumulate in the combustion chamber in large quantities, and ignition may easily lead to an explosion. According to the test data, the spark plug should be opened earlier than the hydrogen valve.

[0126] 4. At time t3, the hydrogen solenoid shut-off valve 8 is opened to supply hydrogen to the combustion chamber. Due to the small molecular weight of hydrogen and its high flow rate in the pipeline, to prevent hydrogen accumulation and explosion caused by the initial injection of hydrogen into the combustion chamber, the hydrogen supply time is delayed through timing control. After entering the combustion chamber, the hydrogen meets the air, and under the action of the spark plug, the hydrogen and air ignite and burn stably. The temperature of the mixture of air, hydrogen, and product water vapor in the combustion chamber begins to rise under the influence of combustion heat.

[0127] 5. At time t4, the temperature of the mixed gas in the combustion chamber reaches equilibrium, the combustion chamber reaches steady state, the ignition process is completed, and the thermal jet experimental device operates in the stable combustion region c under high total temperature conditions.

[0128] 6. At time t5, turn off the spark plug. Because the spark plug is a pulsed high-energy discharge, the two tips of the head are broken down by high voltage to generate a high-temperature electric spark. The spark plug cannot work for a long time. At the same time, hydrogen and air are in a stable combustion condition and can maintain stable combustion without spark plug ignition. Therefore, it is necessary to turn off the spark plug.

[0129] 7. At time t6, under the control of computer 45, the pressure of the hydrogen electronic pressure regulating valve 6 is reduced, decreasing the hydrogen flow rate, while the pressure of the air electronic pressure regulating valve 19 is increased, increasing the air flow rate. Both valves begin to adjust, the hydrogen-to-air equivalence ratio begins to decrease, and the total temperature of the combustion chamber begins to decrease.

[0130] 8. At time t7, the valves for hydrogen and air were regulated, and the flow rates reached a steady state. During the two-way gas flow regulation process from t6 to t7, the combustion chamber maintained stable combustion and did not extinguish. After reaching time t7, the combustion chamber reached the low total temperature region b, where stable combustion was achieved, thus realizing the operation of the thermal jet experimental device at the low total temperature operating point.

[0131] 9. At time t8, the hydrogen electromagnetic shut-off valve 8 is closed, cutting off the hydrogen supply. The hydrogen flow rate becomes 0, and the flame in the combustion chamber is extinguished. The period from t7 to t8 is the actual working time of the thermal jet experimental device in the shock tunnel.

[0132] 10. At time t9, close the air solenoid shut-off valve 21 to cut off the air supply, and the air flow rate becomes 0. The air valve closes a certain time later than the hydrogen valve. Because some hydrogen remains in the pipe between the valve and the combustion chamber after the hydrogen valve closes, it will slowly flow into the combustion chamber, posing a risk of secondary combustion and explosion. Introducing air will blow away the residual hydrogen in the combustion chamber, improving safety.

[0133] 11. At time t10, close all shut-off valves on the hydrogen and air pipelines, and the industrial control computer 45 stops control, thus ending the experiment.

[0134] In the above working method, each step is paused for a different amount of time before proceeding to the next step. The specific pause time is set according to the experimental requirements.

[0135] In this invention, hydrogen and air in the combustion chamber are first ignited under a high equivalence ratio and then stably combusted at a high total temperature. Then, the flow rates of hydrogen and air are precisely adjusted to a low equivalence ratio using an electronic pressure reducing valve, thereby achieving stable combustion at a low total temperature and solving the problem of not being able to work at low total temperature.

[0136] Example 1

[0137] According to the above analysis and experimental data, in order to enable the hot jet experimental device to operate normally under low total temperature conditions of 600K - 898K, combined with the characteristics of the hot jet experimental device, the startup work is as follows:

[0138] 1. Control the equivalence ratio of hydrogen and air so that 0.19 < f < 0.4, that is, ignite the combustion chamber in region c and maintain stable combustion;

[0139] 2. After the hydrogen and air burn stably, output command signals through the industrial control computer 45 to control the hydrogen electronic pressure reducing valve 6 and the air electronic pressure reducing valve 19 respectively. The pressure of hydrogen decreases and the flow rate decreases, while the pressure of air increases and the flow rate increases, and the total temperature of the combustion chamber begins to decrease;

[0140] 3. After accurately controlling the hydrogen electronic pressure reducing valve 6 and the air electronic pressure reducing valve 19 to adjust to the required test point pressure, then stabilize the pressures of the two airflows so that the flow rates of hydrogen and air are stable. At this time, the total equivalence ratio f of hydrogen and air changes to region b, that is, 0.09 < f < 0.19, and stable combustion can still be maintained.

[0141] Example 2

[0142] Taking a certain typical experiment as an example, illustrate the working process of the hot jet experimental device under low total temperature conditions:

[0143] 1. Install and fix the aircraft model 32 with the combustion chamber 30 in the shock tunnel test section 36;

[0144] 2. Evacuate the shock tunnel test section 36 to a vacuum degree of 20 Pa;

[0145] 3. Connect the hydrogen pipeline 13 and the air pipeline 26 to the air inlet of the combustion chamber 30;

[0146] 4. Manually open the hydrogen gas cylinder group 1 and the air gas cylinder 14 to ensure that the pressures of the two gas cylinders are above 10 MPa;

[0147] 5. Manually open the hydrogen manual stop valve 4 and the air manual stop valve 18;

[0148] 6. At the 0th second, input the pressure of the hydrogen electronic pressure regulating valve 6 as 2.11 MPa and the pressure of the air electronic pressure regulating valve 19 as 2.0 MPa in the computer 45. The hydrogen flowmeter 12 and the air flowmeter 25 are both sonic nozzle flowmeters. According to the principle of the sonic nozzle flowmeter, calculate the corresponding hydrogen flow rate of 0.5 g / s, air flow rate of 89.5 g / s, total flow rate of 90 g / s, and total temperature of 898 K at this time;

[0149] 7. In the first second, the air solenoid shut-off valve 21 is opened to supply air to the combustion chamber;

[0150] 8. At the 4th second, open the spark plug for continuous pulse ignition;

[0151] 9. At 4.5 seconds, open the hydrogen solenoid shut-off valve 8 to supply hydrogen to the combustion chamber;

[0152] 10. In the 6th second, the temperature of the gas mixture in the combustion chamber reaches equilibrium, the combustion chamber reaches steady state, the total flow rate of the combustion chamber is 90 g / s, the equivalence ratio f is 0.19, and the total gas temperature is 898 K;

[0153] 11. At 6.5 seconds, turn off the spark plugs;

[0154] 12. In the 7th second, controlled by the industrial control computer 45, the pressure of the hydrogen electronic pressure regulating valve 6 is reduced to 1.5 MPa. According to the principle of the sonic nozzle flow meter, the corresponding hydrogen flow rate is 0.35 g / s. The pressure of the air electronic pressure regulating valve 19 is increased to 2.9 MPa, and the corresponding air flow rate is 134.65 g / s.

[0155] 13. At the 9th second, the valves for hydrogen and air are adjusted and the flow rate reaches a steady state. The total flow rate of the combustion chamber is 135 g / s, the equivalence ratio f is 0.09, and the total gas temperature is 600 K, which means that it has reached the low total temperature region b of stable combustion, thus realizing the operation of the thermal jet experimental device at the low total temperature condition point; the hydrogen and air are ignited and burned inside the combustion chamber 30, and are ejected from the tail of the model through the nozzle 31 to form a supersonic thermal jet flow 33, which is injected into the shock wave wind tunnel test chamber 36;

[0156] 14. At 9.1s, the shock tunnel is started, and high-pressure airflow and shock wave are generated in the shock tube 34. The two are accelerated to supersonic speed through the wind tunnel nozzle 35 and enter the shock tunnel test chamber 36 to form the wind tunnel airflow 37.

[0157] 15. At 9.15s, the wind tunnel airflow 37 blows onto the surface of model 32, exerting force and thermal load on the model, and interacting with the thermal jet airflow 33;

[0158] 16. At the 11th second, the hydrogen solenoid shut-off valve 8 is closed, cutting off the hydrogen supply. The hydrogen flow rate becomes 0, and the flame in the combustion chamber is extinguished.

[0159] 17. At the 13th second, the air solenoid shut-off valve 21 is closed, cutting off the air supply, and the air flow rate becomes 0;

[0160] 18. At 15 seconds, close all shut-off valves on the hydrogen and air pipelines, and the industrial control computer stops control at 45 seconds, ending the experiment.

[0161] The above embodiments are merely exemplary embodiments of this application and are not intended to limit this application. The scope of protection of this application is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to this application within its substance and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of this application.

Claims

1. A method of operating a low total temperature state of a hot-jet experiment apparatus for a shock tunnel, characterized in that, include: 1) Utilizing the principles of stable combustion limit, ignition limit, and high-temperature ablation limit during the combustion process, determine the optimal ignition region for the hydrogen-air combustion equivalence ratio. The equivalence ratio refers to the ratio of the amount of air theoretically required for complete combustion to the actual amount of air supplied during fuel combustion. The optimal ignition zone is the lean oil ignition zone, excluding the high-temperature ablation zone, between the lean oil flame stabilization limit and the lean oil high temperature limit. 2) By controlling the flow rate of hydrogen and air entering the combustion chamber (30) in conjunction with the operation sequence of the thermal jet experimental device, the hydrogen and air combustion equivalence ratio is adjusted to ignite under the condition of the optimal ignition zone, and the combustion chamber (30) is stably combusted under the condition of high total temperature. 3) By precisely adjusting the flow rates of hydrogen and air through the electronic pressure reducing valve, the hydrogen and air combustion equivalence ratio is reduced within the lean ignition zone, and the total temperature of the combustion chamber (30) begins to decrease, so that the combustion chamber (30) continues to burn stably under low total temperature conditions.

2. The operating method of a thermal jet experimental device for a shock tunnel under low total temperature conditions according to claim 1, characterized in that, The optimal ignition region is the ignition region between the lean oil ignition limit and the lean oil high temperature limit.

3. The operating method of a thermal jet experimental device for a shock tunnel under low total temperature conditions according to claim 1, characterized in that, In step 3), the hydrogen and air combustion equivalence ratio is reduced to the flame stability region between the lean flame stabilization limit and the lean ignition limit.

4. The method of claim 1, wherein the method is a method of operating a low total temperature state of a hot-jet experiment apparatus for a shock tunnel, wherein the method further comprises: The working method also includes: Before step 2), first open the air solenoid shut-off valve (21) to supply air to the combustion chamber, then turn on the spark plug for continuous pulse ignition and open the hydrogen valve.

5. The method of claim 1, wherein the method further comprises: The working method also includes: After step 2), the hydrogen and air are in a stable combustion condition, so turn off the spark plug.

6. The method of claim 1, wherein the method is a method of operating a low total temperature state of a hot-jet experiment apparatus for a shock tunnel, wherein the method comprises: The working method also includes: The shutdown process of the thermal jet experimental device is as follows: First, close the hydrogen electromagnetic shut-off valve (8) to cut off the hydrogen supply. After the hydrogen flow rate becomes 0 and the flame in the combustion chamber is extinguished, close the air electromagnetic shut-off valve (21) to cut off the air supply. The air flow rate becomes 0. Then, close all the shut-off valves on the hydrogen and air pipelines. The industrial control computer (45) stops control and the experiment ends.

7. A method of operating a low total temperature state of a hot-jet experiment apparatus for a shock tunnel according to claim 2 or 3, characterized in that In the aforementioned working method The lean oil flame stabilization limit is 0.09, the lean oil ignition limit is 0.19, and the lean oil high temperature limit is 0.

4.

8. A method of operating a low total temperature state of a hot-jet experiment apparatus for a shock tunnel according to any one of claims 1 to 6, characterized in that In the described working method, the next step is performed only after each step has a different duration.

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