Variable excitation direction broadband pulse gun-combustion chamber acoustic oscillation experimental system

Abstract

Variable excitation direction wide frequency domain pulse gun-burner acoustic oscillation experiment system belongs to the field of liquid rocket engine combustion chamber combustion stability evaluation. The present application comprises a pulse gun, a combustion chamber and a pressure test system. The main structure of the pulse gun comprises an igniter, a gun barrel, solid fuel, an O-ring, a brass diaphragm, a brass diaphragm gasket, and a gun barrel. The main structure of the combustion chamber is divided into a flange cover, a cavity, a metal bolt and a nut. The combustion chamber is mainly used for simulating the actual engine combustion chamber at the acoustic frequency. The pressure test system comprises a pressure sensor array and a data acquisition system. The pressure sensor array is used for real-time online measurement of the dynamic pressure at each position in the pulse gun and the combustion chamber. The present application can realize axial, radial and tangential pulse excitation directions; and has a wide range of acoustic frequencies of the combustion chamber, a wide range of back pressure of the combustion chamber and different atmosphere environments. Among them, different atmosphere environments affect the acoustic oscillation by affecting the size of the sound velocity.

Description

Technical Field

[0001] This invention belongs to the field of combustion stability assessment of liquid rocket engine combustors, and relates to an experimental system for analyzing the acoustic oscillation characteristics of combustors using a pulse gun. Background Technology

[0002] The mechanical and thermal environment within liquid rocket engines is extremely harsh. The high-pressure, high-flow-rate propellant flow and combustion process easily induce various forms of disturbances, which can then couple with the propellant supply and combustion process, causing large-amplitude, periodic pressure oscillations within the combustion chamber—a phenomenon known as combustion instability. This can lead to engine structural damage or combustion chamber ablation, ultimately resulting in engine failure. Therefore, combustion instability is one of the key challenges in the development and reliability assurance of liquid rocket engines.

[0003] To test the combustion stability of liquid rocket engine combustors and their ability to resist combustion instabilities, corresponding combustion stability tests need to be conducted at different stages of development. A common method is to install artificial excitation devices at specific locations within the combustor. In my country, pulse guns are often used in engineering to introduce pulse disturbances, and the stability of the combustor is evaluated by measuring the decay time of the pressure oscillations generated by the pulse disturbances.

[0004] The pressure oscillation frequencies of combustion instability range from hundreds to thousands of Hz, often coinciding with the acoustic characteristic frequencies of the combustion chamber. Multiple different modes, including longitudinal, transverse, and tangential modes, may coexist. The mechanisms of their generation, development, and decay are complex, making assessment difficult. Therefore, research on engineering experiments using pulse guns for combustion stability assessment needs to focus on how to excite multiple modes over a wide frequency range. Developing a wide-frequency-range pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction and studying the excitation, development, and decay processes of each acoustic mode is of great significance for practical engineering experiments.

[0005] Existing literature and patents have revealed the structures of several disturbance devices for pulse guns or combustion stability assessment tests, as well as methods for controlling propellant dosage for certain types of engines. However, these methods are only applicable to engineering tests and not suitable for mechanistic studies. Furthermore, existing combustion chamber acoustic oscillation experimental systems often use horns as disturbance sources, resulting in low excitation amplitudes that do not meet the needs of practical engineering applications; or they operate at atmospheric pressure, which is inconsistent with the high-pressure environment of actual engine combustion chambers; and the excitation direction of the disturbance is singular, failing to reveal changes in acoustic modal oscillation characteristics caused by different excitation directions. Summary of the Invention

[0006] The purpose of this invention is to provide a wide-frequency-domain pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction, capable of achieving axial, radial, and tangential pulse excitation directions; and possessing a wide range of combustion chamber acoustic frequencies, a wide range of combustion chamber back pressure, and different atmospheric environments. The different atmospheric environments affect the acoustic oscillation by influencing the speed of sound.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] The present invention discloses a wide-frequency-domain pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction, comprising a pulse gun, a combustion chamber, and a pressure testing system.

[0009] The pulse gun's main structure comprises seven parts: an igniter, a cannon, solid fuel, an O-ring, a brass diaphragm, a brass diaphragm gasket, and a barrel. The igniter, cannon, and barrel are all connected by threads. A brass diaphragm gasket provides the first layer of sealing between the cannon and barrel, while an O-ring provides a second layer of radial sealing. The solid fuel is loaded into the cannon and ignited by the high temperature or electric spark generated by the igniter. The resulting high-temperature gas pressurizes the cannon, reaching the rupture pressure of the brass diaphragm, at which point the diaphragm ruptures. The high-pressure gas then forms a shock wave within the barrel and propagates downstream. The size of the brass diaphragm is determined by the required rupture pressure, while the size of the solid fuel is determined by practical constraints such as gas production rate, experimental costs, and safety.

[0010] Furthermore, the solid fuel is black powder, and the brass diaphragm is a rupture disc.

[0011] Furthermore, the performance of the pulse gun is described by measured internal ballistic curves, with the main parameters being: peak internal pressure p. max The internal pressure of the gun rises from 0 to p max Required time t p The propagation speed V of the shock wave inside the gun barrel S =δx / Δt, where δx is the distance between two pressure measuring points in the barrel, and Δt is the time difference between the pressure peak values ​​in the pressure-time curves of the two pressure measuring points in the barrel.

[0012] The main structure of the combustion chamber consists of a flange cover, a cavity, metal bolts, and nuts. The combustion chamber is primarily used to simulate the actual engine combustion chamber at acoustic frequencies. Its internal cavity dimensions, such as the axial length L and inner diameter a, are determined by the required acoustic characteristic frequency f. mnq The decision is made using the formula for calculating the acoustic frequency of a cylinder:

[0013]

[0014] Where: m is the angular mode number (non-negative integer, m = 0, 1, 2, ...), representing the number of nodes of the sound pressure in the circumferential direction; n is the radial mode number (non-negative integer, n = 0, 1, 2, ...), representing the number of nodes of the sound pressure in the radial direction; q is the angular mode number (non-negative integer, q = 0, 1, 2, ...), representing the number of nodes of the sound pressure in the axial direction; β is the average speed of sound in the medium; mn The derivative of the Bessel function J′ m The nth positive root of (x) satisfies J′ m (β mn ) = 0.

[0015] The flange cover and the cavity are connected by metal bolts and nuts, and sealed by axially tightening O-rings. The flange cover is equipped with an axial pulse gun interface, an air inlet interface, and a static pressure sensor interface, while the cavity is equipped with radial and tangential pulse gun interfaces, a dynamic pressure sensor interface, and an exhaust interface.

[0016] Furthermore, by mounting the pulse gun on three different interfaces, different pulse excitation directions can be achieved; by changing dimensional parameters such as length L and inner diameter a, simulations of combustion chambers with different characteristic frequencies can be realized; for a combustion chamber with a fixed length L and inner diameter a, by changing the modal orders m, n, and q in the radial, tangential, and longitudinal directions, multiple different modes with frequencies ranging from hundreds to thousands of Hz can be obtained, realizing wide-frequency domain, multi-modal oscillation experiments; by introducing safety gases of different densities into the combustion chamber, controlling the intake and exhaust volumes, and using a static pressure sensor to monitor the internal pressure in real time, oscillation experiments can be achieved in a wide back pressure range of 0.1–25 MPa under different atmospheric environments. Safety gases include non-flammable or inert gases such as nitrogen, argon, and carbon dioxide.

[0017] The combustion chamber can simulate the chamber pressure environment under two actual engine operating conditions: the first is that after filling the combustion chamber with safe gas to a certain pressure value, the intake and exhaust valves are kept closed. At this time, the engine is in a stable operating state and the chamber pressure remains basically unchanged. The second is that the intake and exhaust volume of the combustion chamber is controlled to gradually increase or decrease the pressure value. At this time, the engine is in an ignition boost or thrust adjustment state and the chamber pressure has a dynamic change process.

[0018] Furthermore, the acoustic oscillation characteristics of the combustion chamber are described by the following parameters: pressure oscillation frequency f, amplitude A of the mode at frequency f, mode shape distribution at frequency f, and attenuation coefficient α of the mode at frequency f. Wherein:

[0019] ① The pressure oscillation frequency f, the amplitude A of the mode at frequency f, and the mode shape distribution at frequency f are obtained by the following method: Perform Fast Fourier Transform (FFT) on the pressure-time data of the measuring point to obtain the amplitude-frequency diagram of the measuring point, and directly read the peak frequency f and the corresponding amplitude A from the diagram; plot the amplitude A-different measuring point positions to obtain the mode shape distribution at frequency f.

[0020] ② The attenuation coefficient α of the mode at frequency f is obtained by the following method: the pressure-time data at a certain measuring point in the combustion chamber is bandpass filtered near the frequency f, and the filtered curve is taken in the range of t1 to t2. n The peak pressure at time p1~p n Calculate α using the following formula:

[0021]

[0022] The pressure testing system includes a pressure sensor array and a data acquisition system. The pressure sensor array is used to measure the dynamic pressure at various locations within the pulse gun and combustion chamber in real time. The data acquisition system is used to collect the pressure information measured by the sensors.

[0023] Furthermore, the pressure sensor array includes a piezoelectric dynamic pressure sensor, a piezoresistive dynamic pressure sensor, and a static pressure sensor. The piezoelectric dynamic pressure sensor is used for real-time online measurement of the dynamic pressure within the pulse gun, with a range of 0–100 MPa, an accuracy of 1% FS, and a natural frequency up to 150 kHz. The piezoresistive dynamic pressure sensor has a range of 0–15 MPa or 0–25 MPa, an accuracy of 0.25% FS, and a resonant frequency up to 461.6 kHz. The static pressure sensor has a range of 0–25 MPa and an accuracy of 0.25% FS.

[0024] The data acquisition system includes a charge conditioner and a data acquisition unit. The charge conditioner converts the charge signal output from the piezoelectric high-frequency dynamic pressure sensor into a voltage signal for easy acquisition by the data acquisition unit, and has four channels. The data acquisition unit has 16 channels, acquiring data at a maximum sampling rate of 256kHz, and connects to a computer via a gigabit network cable.

[0025] The working method of the variable excitation direction broadband pulse gun-combustion chamber acoustic oscillation experimental system disclosed in this invention is as follows: Assemble and fix the combustion chamber on the experimental stand, connect the gas path, and install a piezoresistive dynamic pressure sensor on the corresponding interface of the combustion chamber. Assemble and install the pulse gun on the axial, radial, or tangential interface of the combustion chamber, and install a piezoelectric dynamic pressure sensor on the corresponding interface of the pulse gun. Seal all unused pulse gun and sensor interfaces with plugs, connect all cables, and ensure that the pressure testing system is working properly.

[0026] When simulating a stable engine operating state: close the exhaust valve, open the intake valve, introduce safety gas into the combustion chamber, observe the static pressure sensor reading, and close the intake valve after the required back pressure is reached.

[0027] When simulating engine ignition boost or thrust adjustment: adjust the opening of the intake and exhaust valves respectively, introduce safety gas into the combustion chamber, observe the reading of the static pressure sensor, and gradually increase or decrease the back pressure.

[0028] The igniter is powered on and ignited, simultaneously sending a trigger signal to the data acquisition unit to initiate synchronous data acquisition. Solid fuel inside the pulse gun is ignited and combusted, generating a large amount of high-temperature gas that rapidly pressurizes the gun. Once the pressure reaches the rupture pressure of the brass diaphragm, the diaphragm breaks, and the high-pressure gas forms a high-pressure pulse in the barrel, which is rapidly injected into the combustion chamber, creating pulse excitation. The sensor array measures the dynamic pressure in real time, and the data is acquired by the data acquisition system. Once the readings of each pressure sensor stabilize, the data acquisition ends. The intake valve is closed, the exhaust valve is opened, and the gas in the combustion chamber is expelled, concluding the wideband pulse gun-combustion chamber acoustic oscillation experiment.

[0029] Beneficial effects:

[0030] 1. The variable excitation direction wideband pulse gun-combustion chamber acoustic oscillation experimental system disclosed in this invention, when filled with safety gases of different properties such as nitrogen and argon in a cold state, can maintain the back pressure at any fixed value between 0.1 and 25 MPa, simulating the chamber pressure environment under stable engine operating conditions. By controlling the opening of the intake and exhaust valves, the back pressure can be dynamically varied within the range of 0.1 to 25 MPa, simulating the chamber pressure environment under engine ignition boost or thrust adjustment conditions. Therefore, the experimental system can simulate the pressure environment of the combustion chamber over a wide pressure range and under different atmospheric conditions.

[0031] 2. The variable excitation direction wideband pulse gun-combustion chamber acoustic oscillation experimental system disclosed in this invention considers the essential similarity between simulated and real phenomena. It uses the same natural frequency as the actual engine combustion chamber to calculate the dimensional parameters of the combustion chamber in the experimental system. Therefore, only the relevant dimensional parameters need to be changed to simulate engine combustion chambers with different natural frequencies. The combustion chamber is simultaneously equipped with axial, radial, and tangential pulse gun interfaces. Different pulse gun interfaces correspond to different pulse incident directions, enabling the introduction of pulse excitation disturbances into the combustion chamber from the axial, radial, and tangential directions, thereby simultaneously exciting different acoustic modes in the combustion chamber, corresponding to different oscillation frequencies. Therefore, this experimental system can study the acoustic oscillation characteristics of the combustion chamber over a wide frequency range.

[0032] 3. The variable excitation direction wideband pulse gun-combustion chamber acoustic oscillation experimental system disclosed in this invention uses high-pressure gas generated by solid fuel combustion to break through a brass diaphragm and form a high-pressure amplitude pulse disturbance. The amplitude of the pulse disturbance is related to the amount of solid fuel and the rupture pressure of the brass diaphragm. The mass of solid fuel and the rupture pressure of the brass diaphragm can be changed according to actual needs. Therefore, the pulse disturbance performance output by the pulse gun is controllable, and thus the acoustic oscillation range is controllable.

[0033] 4. The variable excitation direction broadband pulse gun-combustion chamber acoustic oscillation experimental system disclosed in this invention uses a high-frequency, high-precision pressure sensor to measure the dynamic pressure process in the pulse gun and combustion chamber. Pressure data at each measuring point can be obtained in a single experiment. In the post-processing process, the performance parameters of the pulse gun, as well as the acoustic characteristic parameters such as the frequency, amplitude, mode, and attenuation process of the pressure oscillation in the combustion chamber, can be obtained from these data. This helps to study the propagation and attenuation mechanism of pressure disturbance in the combustion chamber and the formation process of different mode shapes of pressure oscillation, which helps to improve the combustion stability of the pulse gun and thus improve the stability of the broadband pulse gun-combustion chamber acoustic oscillation experiment. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the experimental device for the variable excitation direction broadband pulse gun-combustion chamber acoustic oscillation system disclosed in this invention.

[0035] Wherein: 1—Pulse gun, 2—Combustion chamber, 3.1—Piezoelectric dynamic pressure sensor, 3.2—Piezoelectric dynamic pressure sensor, 3.3—Charge conditioner, 3.4—Static pressure sensor, 3.5—Data acquisition instrument.

[0036] Figure 2 This is a schematic diagram of an experimental system for analyzing the acoustic oscillation characteristics of a combustion chamber using pulse excitation.

[0037] Figure 3 This is a structural diagram of a pulse gun;

[0038] Wherein: 1.1—Igniter, 1.2—Gun, 1.3—Solid fuel, 1.4—O-ring, 1.5—Brass diaphragm, 1.6—Brass diaphragm gasket, 1.7—Gun barrel.

[0039] Figure 4 This is a structural diagram of the combustion chamber;

[0040] Wherein: 2.1—Flange cover, 2.2—Cavity, 2.3—Metal bolts and nuts. Detailed Implementation

[0041] To better illustrate the purpose and advantages of the present invention, the invention will be further described below in conjunction with the accompanying drawings and examples.

[0042] Example 1:

[0043] like Figure 1 As shown, the variable excitation direction broadband pulse gun-combustion chamber acoustic oscillation experimental system disclosed in this example consists of a pulse gun 1, a combustion chamber 2, and a pressure testing system 3. The pressure testing system 3 comprises 3.1 a piezoelectric dynamic pressure sensor, 3.2 a piezoresistive dynamic pressure sensor, 3.3 a charge conditioner, 3.4 a static pressure sensor, and 3.5 a data acquisition unit.

[0044] The principle of the experimental system is as follows Figure 2 As shown, the combustion chamber 2 is pressurized to a specified pressure via a gas cylinder. Pressing the ignition switch connects the ignition circuit and simultaneously sends a trigger signal to the data acquisition instrument 3.5. At this time, the solid fuel 1.3 in the pulse gun 1 is ignited by the igniter 1.1, and the data acquisition instrument 3.5 begins data acquisition. The combustion of the solid fuel 1.3 in the pulse gun 1 generates a large amount of high-temperature gas, causing the pressure inside the gun 1.2 to rise rapidly. Once the pressure reaches the rupture pressure of the brass diaphragm 1.5, the brass diaphragm 1.5 ruptures, and the high-temperature, high-pressure gas forms a shock wave through the gun barrel 1.7 and is injected into the combustion chamber 2, acting as a pulse excitation to generate pressure oscillations that decay over time. The piezoelectric dynamic pressure sensor 3.1 measures the pressure-time data at each measuring point inside the pulse gun 1 throughout the entire process, and outputs it in real time as a charge signal to the charge conditioner 3.3. The charge conditioner 3.3 converts the received charge signal into a voltage signal in real time and outputs it to the data acquisition instrument 3.5. The piezoresistive dynamic pressure sensor 3.2 measures the pressure-time data at each measuring point inside the combustion chamber 2 throughout the entire process, and outputs it in real time as a voltage signal to the data acquisition instrument 3.5. The data acquisition instrument 3.5 is connected to an external computer to store the measurement data. Power is required for the igniter 1.1, the piezoresistive dynamic pressure sensor 3.2, the charge conditioner 3.3, the data acquisition instrument 3.5, and the computer in the experimental system.

[0045] As an alternative, the data acquisition instrument 3.5 can be changed to pressure triggering, that is, data acquisition begins when the static pressure sensor 3.4 reaches the specified pressure.

[0046] Pulse gun 1 Figure 3As shown, it consists of an igniter 1.1, a gun 1.2, solid fuel 1.3, an O-ring 1.4, a brass diaphragm 1.5, a brass diaphragm gasket 1.6, and a barrel 1.7. It also has reserved interfaces for three piezoelectric dynamic pressure sensors 3.1 and an emergency pressure relief valve interface. The assembly method of the pulse gun 1 is as follows: First, use a small amount of high-vacuum silicone grease to attach the brass diaphragm 1.5 to one side of the flat surface of the brass diaphragm washer 1.6; then, insert the side of the brass diaphragm washer 1.6 with the conical protrusion into the conical countersunk hole of the barrel 1.7, and keep the barrel 1.7 vertical; after inserting the O-ring 1.4 into the O-ring groove of the gun 1.2, screw the gun 1.2 into the barrel 1.7 through the thread and tighten it. At this time, the gun 1.2 presses the brass diaphragm 1.5 and the brass diaphragm washer 1.6 together to achieve the first seal, and the O-ring is the second seal; finally, put solid fuel 1.3 into the gun, install the igniter 1.1 and tighten the combined gasket. In the experiment, different models of brass diaphragms 1.5 and different masses of solid fuel 1.3 can be selected according to actual needs; the type of igniter 1.1 can also be changed according to actual conditions, as long as the installation threads are matched.

[0047] The structure of combustion chamber 2 is as follows Figure 4 As shown, the combustion chamber 2 consists of a flange cover 2.1, a cavity 2.2, and metal bolts and nuts 2.3. The assembly method for the combustion chamber 2 is as follows: place the O-ring into the groove on the flange face of the cavity 2.2, then press the flange cover 2.1 onto the flange face of the cavity 2.2, and secure the flange cover 2.1 and the cavity 2.2 together with metal bolts and nuts 2.3. The combustion chamber 2 has one axial interface for a pulse gun 1, one intake valve interface, and one static pressure sensor adapter interface pre-installed on the flange cover 2.1; and one radial interface for a pulse gun 1, one tangential interface for a pulse gun 1, eight piezoresistive dynamic pressure sensor interfaces 3.2, and one exhaust valve interface pre-installed on the cavity 2.2.

[0048] Example 2:

[0049] This embodiment is used to simulate radial pulse excitation of the combustion chamber when the engine is operating stably. The preset experimental conditions are: back pressure of 6MPa in combustion chamber 2, 6 grams of black powder in solid fuel 1.3, rupture pressure of 60MPa in brass diaphragm 1.5, pulse gun 1 installed on radial interface, 3 pressure measuring points on pulse gun 1, 4 measuring points on combustion chamber 2, and data acquisition instrument 3.5 collecting data for about 60 seconds after the ignition signal is issued.

[0050] This example discloses a broadband pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction. The specific implementation steps are as follows:

[0051] Step 1: Assemble the combustion chamber 2 according to the assembly method described above, and fix it in place. Figure 1On the experimental stand shown, use the appropriate type of plug to plug the axial and tangential interfaces of the pulse gun 1, as well as the unused piezoresistive dynamic pressure sensor 3.2 interface.

[0052] Step 2: Connect the inlet and outlet valves, as well as the corresponding gas pipelines, valves, gas cylinders, etc. Keep the gas cylinder closed and the inlet and outlet valves open, and install the piezoresistive dynamic pressure sensor 3.2.

[0053] Step 3: Assemble the pulse gun 1 according to the assembly method described above, and install it on the radial interface of the cavity 2.2. Then install the piezoelectric dynamic pressure sensor 3.1 and the emergency pressure relief valve.

[0054] Step 4: Connect all circuits and signal cables except for the igniter power supply. Confirm that the zero point and noise of all sensors are correct and reasonable. Close the exhaust valve, open the gas cylinder and adjust the pressure reducing valve to introduce safety gas into the combustion chamber. At the same time, observe the real-time reading of the static pressure sensor 3.4 on the computer. When it stabilizes at around 6MPa, close the intake valve, pressure reducing valve and gas cylinder.

[0055] Step 5: Connect the ignition circuit and turn on the ignition switch. Ignition 1.1 starts working, and data acquisition instrument 3.5 starts collecting data. Solid fuel 1.3 is ignited and burns violently, producing a large amount of high-temperature gas. This rapidly increases the pressure inside the gun 1.2, reaching approximately 60 MPa. At this point, the brass diaphragm 1.5 ruptures, generating a high-pressure pulse, which, along with the gas, is injected into the combustion chamber 2 through the barrel 1.7, exciting pressure oscillations.

[0056] Step 6: After the data acquisition instrument 3.5 has been collecting data for about 60 seconds, manually stop it and slowly open the exhaust valve to depressurize and exhaust the entire system. The pulse excitation experiment is completed under this condition.

[0057] In this embodiment, the safety gas introduced from the gas cylinder into the combustion chamber 2 is nitrogen.

[0058] Example 3:

[0059] This embodiment is used to simulate radial pulse excitation of the combustion chamber when the engine thrust is gradually increased. The preset experimental conditions are: the back pressure of combustion chamber 2 increases from 10MPa to 20MPa, the solid fuel 1.3 is 10 grams of black powder, the rupture pressure of the brass diaphragm 1.5 is 90MPa, the pulse gun 1 is installed on the radial interface, the pulse gun 1 has 3 pressure measuring points, the combustion chamber 2 has 4 measuring points, and the data acquisition instrument 3.5 is pressure triggered for data acquisition.

[0060] The experimental system for wideband pulse gun-combustion chamber acoustic oscillation with variable excitation direction disclosed in this example is implemented in the following steps:

[0061] Step 1: Assemble the combustion chamber 2 according to the assembly method described above, and fix it in place. Figure 1 On the experimental stand shown, use the appropriate type of plug to plug the axial and tangential interfaces of the pulse gun 1, as well as the unused piezoresistive dynamic pressure sensor 3.2 interface.

[0062] Step 2: Connect the inlet and outlet valves, as well as the corresponding gas pipelines, valves, gas cylinders, etc. Keep the gas cylinder closed and the inlet and outlet valves open, and install the piezoresistive dynamic pressure sensor 3.2.

[0063] Step 3: Assemble the pulse gun 1 according to the assembly method described above, and install it on the radial interface of the cavity 2.2. Then install the piezoelectric dynamic pressure sensor 3.1 and the emergency pressure relief valve.

[0064] Step 4: After connecting all circuits and signal cables, confirm that the zero points and noise levels of all sensors are correct and reasonable, and adjust the acquisition mode of the data acquisition instrument 3.5 to pressure trigger. Close the exhaust valve, open the gas cylinder and adjust the pressure reducing valve to introduce safety gas into the combustion chamber. Control the combustion chamber pressurization rate by controlling the opening of the intake valve. When the real-time reading of the static pressure sensor 3.4 reaches 10 MPa, the acquisition will be automatically triggered.

[0065] Step 5: After the data acquisition device 3.5 is triggered, the ignition switch is immediately turned on, and the igniter 1.1 begins to work. The solid fuel 1.3 is ignited and burns violently, producing a large amount of high-temperature gas, which rapidly increases the pressure inside the gun 1.2. When the pressure reaches about 90 MPa, the brass diaphragm 1.5 ruptures and generates a high-pressure pulse, which, along with the gas, is injected into the combustion chamber 2 through the barrel 1.7, exciting pressure oscillations.

[0066] Step 6: When the real-time reading of the static pressure sensor 3.4 reaches 20MPa, manually close the intake valve and stop data acquisition. Slowly open the exhaust valve to depressurize and exhaust the entire system. Under this condition, the pulse excitation experiment is completed.

[0067] In this embodiment, the safety gas introduced from the gas cylinder into the combustion chamber 2 is nitrogen.

[0068] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific implementation process of the present invention and is used to explain the present invention. It is not intended to limit the scope of protection of the present invention. 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 broadband pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction, characterized in that: Includes a pulse gun, combustion chamber, and pressure testing system; The main structure of the pulse gun includes an igniter, a cannon, solid fuel, an O-ring, a brass diaphragm, a brass diaphragm gasket, and a barrel. The igniter, cannon, and barrel are all connected by threads. The brass diaphragm gasket is used to press the brass diaphragm between the cannon and the barrel to achieve the first seal, and the O-ring provides the second radial seal. The solid fuel is loaded in the cannon and is ignited and burned by the high temperature or electric spark generated by the igniter. The high-temperature gas increases the pressure inside the cannon. When the diaphragm ruptures, the brass diaphragm breaks, and the high-pressure gas forms a shock wave in the barrel and propagates downstream. The size of the brass diaphragm is determined by the required rupture pressure, and the size of the solid fuel is determined by actual constraints. The main structure of the combustion chamber consists of a flange cover, a cavity, metal bolts, and nuts; the combustion chamber is mainly used to simulate the actual engine combustion chamber at acoustic frequencies. The pressure testing system includes a pressure sensor array and a data acquisition system; the pressure sensor array is used to measure the dynamic pressure at various locations within the pulse gun and combustion chamber in real time. The data acquisition system is used to collect pressure information measured by sensors; The pressure sensor array includes piezoelectric dynamic pressure sensors, piezoresistive dynamic pressure sensors, and static pressure sensors; The data acquisition system includes a charge conditioner and a data acquisition instrument; The performance of a pulse gun is described by measured internal ballistic curves. Key parameters include: peak internal pressure of the gun. The pressure inside the gun rose from 0 to Time required The propagation speed of the shock wave inside the gun barrel ,in This is the distance between two pressure measuring points in the barrel. The time difference between the pressure peak values ​​in the pressure-time curves of two pressure measuring points in the barrel; Axial length of the internal cavity of the engine combustion chamber , inner diameter The size is determined by the required acoustic characteristic frequency. The decision is made using the formula for calculating the acoustic frequency of a cylinder: in: Let be the angular modal number, and be a non-negative integer. , representing the number of nodes of the sound pressure in the circumferential direction; The radial mode number is a non-negative integer. , representing the number of nodes in the radial direction of the sound pressure; The angular mode number is a non-negative integer. , representing the number of nodes of the sound pressure along the axial direction; The average speed of sound in the medium; The derivative of the Bessel function The A positive root, satisfying ; The flange cover and the cavity are connected by metal bolts and nuts, and sealed by axially tightening O-rings; the flange cover is equipped with an axial pulse gun interface, an air inlet interface and a static pressure sensor interface, and the cavity is equipped with radial and tangential pulse gun interfaces, a dynamic pressure sensor interface and an exhaust interface.

2. The wideband pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction as described in claim 1, characterized in that: Different pulse excitation directions are achieved by mounting the pulse gun on three different interfaces; the length is changed. , inner diameter Dimensional parameters enable simulation of combustion chambers with different characteristic frequencies; for fixed lengths... , inner diameter The combustion chamber, by changing the modal orders in the radial, tangential, and longitudinal directions. , , It can obtain various modes with frequencies ranging from hundreds to thousands of Hz, realizing wide-frequency domain and multi-mode oscillation experiments; by introducing safety gases of different densities into the combustion chamber, controlling the intake and exhaust volume, and using a static pressure sensor to monitor the internal pressure in real time, it can realize oscillation experiments in a wide back pressure range of 0.1~25MPa and different atmospheric environments; the safety gases include non-flammable or inert gases such as nitrogen, argon, and carbon dioxide.

3. The wideband pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction as described in claim 2, characterized in that: The combustion chamber is used to simulate the chamber pressure environment under two engine operating conditions: the first is to fill the combustion chamber with safe gas to a certain pressure value and keep the intake and exhaust valves closed, which corresponds to the stable operating state of the engine and the chamber pressure remains basically unchanged; the second is to control the intake and exhaust volume of the combustion chamber to gradually increase or decrease the pressure value, which corresponds to the ignition boost or thrust adjustment state of the engine and the chamber pressure undergoes a dynamic change process.

4. The wideband pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction as described in claim 1, characterized in that: The acoustic oscillation characteristics of the combustion chamber are described by the following parameter: pressure oscillation frequency. The frequency is The amplitude of the mode The frequency is The modal shape distribution, with frequencies of The modal attenuation coefficient ;in: ① Pressure oscillation frequency , frequency is The amplitude of the mode , frequency is The modal shape distribution was obtained by performing a Fast Fourier Transform (FFT) on the pressure-time data at the measuring point to obtain the amplitude-frequency plot of that point, and then directly reading the peak frequency from the plot. and the corresponding amplitude ; Plot amplitude —Images at different measurement point locations yielded frequencies of Modal shape distribution; ② Frequency is The modal attenuation coefficient The pressure-time data at a certain measuring point in the combustion chamber was obtained using the following method at a frequency... Nearby bandpass filtering, take the filtered curve at Peak pressure at any moment Calculate using the following formula : 。 5. The wideband pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction as described in claim 1, characterized in that: Piezoelectric dynamic pressure sensors are used for real-time online measurement of dynamic pressure inside pulse guns, with a range of 0~100MPa, an accuracy of 1% FS, and a natural frequency up to 150kHz; piezoresistive dynamic pressure sensors have a range of 0~15MPa or 0~25MPa, an accuracy of 0.25%FS, and a resonant frequency up to 461.6kHz; static pressure sensors have a range of 0~25MPa and an accuracy of 0.25%FS.

6. The wideband pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction as described in claim 1, characterized in that: The charge conditioner is used to convert the charge signal output by the piezoelectric high-frequency dynamic pressure sensor into a voltage signal for easy acquisition by the data acquisition instrument. It has 4 channels. The data acquisition instrument has 16 channels and acquires data at a maximum sampling rate of 256kHz. It is connected to the computer via a gigabit network cable.

7. The wideband pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction as described in claim 1, characterized in that: The solid fuel is black powder, and the brass diaphragm is a rupture disc.

8. The broadband pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction as described in any one of claims 1, 2, 3, 4, 5, 6, or 7, characterized in that: Assemble and fix the combustion chamber on the test bench, connect the gas line, and install the piezoresistive dynamic pressure sensor on the corresponding interface of the combustion chamber; assemble and install the pulse gun on the axial, radial or tangential interface of the combustion chamber, and install the piezoelectric dynamic pressure sensor on the corresponding interface of the pulse gun; seal all unused pulse gun and sensor interfaces with plugs, connect all cables, and ensure that the pressure testing system is working properly; When simulating a stable engine operating state: close the exhaust valve, open the intake valve, introduce safety gas into the combustion chamber, observe the static pressure sensor reading, and close the intake valve after the required back pressure is reached. When simulating engine ignition boost or thrust adjustment: adjust the opening of the intake and exhaust valves respectively, introduce safety gas into the combustion chamber, observe the reading of the static pressure sensor, and gradually increase or decrease the back pressure; The igniter is powered on and ignited, simultaneously sending a trigger signal to the data acquisition unit to trigger synchronous acquisition. The solid fuel inside the pulse gun is ignited and burned, generating a large amount of high-temperature gas that rapidly pressurizes the gun. Once the pressure reaches the rupture pressure of the brass diaphragm, the brass diaphragm ruptures, and the high-pressure gas forms a high-pressure pulse in the barrel, which is then rapidly injected into the combustion chamber, creating pulse excitation. The sensor array measures the dynamic pressure in real time, and the data is acquired by the data acquisition system. Once the readings of each pressure sensor stabilize, the acquisition ends. The intake valve is closed, the exhaust valve is opened, and the gas in the combustion chamber is discharged, thus ending the wideband pulse gun-combustion chamber acoustic oscillation experiment.

Images