Wideband-domain pulse gun-combustion chamber acoustic oscillation experiment system with variable excitation direction

Abstract

The invention discloses a wide-frequency-domain pulse gun-combustion chamber acoustic oscillation experiment system with a variable excitation direction, and belongs to the field of evaluation of combustion stability of combustion chambers of liquid-propellant rocket engines. The device comprises a pulse gun, a combustion chamber and a pressure testing system. The pulse gun main body structure comprises an igniter, a gun blunderbuss, solid fuel, an O-shaped ring, a brass diaphragm, a brass diaphragm gasket and a gun barrel. A combustion chamber main body structure is divided into a flange cover, a cavity, a metal bolt and a nut. The combustion chamber is mainly used for simulating an actual engine combustion chamber at acoustic frequency. The pressure test system comprises a pressure sensor array and a data acquisition system. And the pressure sensor array is used for measuring the dynamic pressure of each position in the pulse gun and the combustion chamber online in real time. According to the invention, axial, radial and tangential pulse excitation directions can be realized; and a wide combustion chamber acoustic frequency range, a wide combustion chamber back pressure range and different atmosphere environments are achieved. Wherein different atmosphere environments influence acoustic oscillation by influencing the sound velocity.

Description

Technical Field

[0001] The invention belongs to the field of combustion stability evaluation of liquid rocket engine combustion chambers and relates to an experimental system for analyzing the acoustic oscillation characteristics of combustion chambers using a pulse gun. Background Art

[0002] The thermal and mechanical environment within a liquid rocket engine is extremely harsh. The high-pressure, high-flow propellant flow and combustion process easily induce various forms of disturbances, which can then form a coupled feedback loop with the propellant supply and combustion process, causing large, periodic pressure oscillations within the combustion chamber. This phenomenon, known as combustion instability, can lead to structural damage or combustion chamber erosion, ultimately causing engine failure. Therefore, combustion instability is a key issue facing the development and reliability of liquid rocket engines.

[0003] To test the combustion stability of liquid rocket engine combustion chambers and their ability to resist combustion instabilities, appropriate combustion stability tests are conducted at different stages of development. A common method involves installing artificial excitation devices at specific locations in the combustion chamber. In Chinese engineering, pulse guns are often used to introduce pulse perturbations. The stability of the combustion chamber is assessed by measuring the decay time of the pressure oscillations induced by these pulse perturbations.

[0004] The pressure oscillation frequency of combustion instability ranges from several hundred Hz to several thousand Hz, often coinciding with the acoustic characteristic frequency of the combustion chamber. Multiple different modes, such as longitudinal, transverse, and tangential, may coexist. The mechanisms of their generation, development, and attenuation are complex, making evaluation difficult. Therefore, research on engineering experiments using pulse guns for combustion stability assessment needs to focus on how to excite multiple modes across a wide frequency domain. Developing a wide-frequency pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction and studying the excitation, development, and attenuation of each acoustic mode is of great significance for actual engineering experiments.

[0005] Existing literature and patents have revealed several structures for pulse guns or perturbation devices used in combustion stability characterization tests, as well as methods for controlling charge dosage for certain types of engines. However, these methods are only suitable for engineering tests and are not suitable for mechanistic research. Existing combustion chamber acoustic oscillation experimental systems often use speakers as perturbation sources, but these have low excitation amplitudes, which are not suitable for practical engineering applications. They are also operated at atmospheric pressure, which is inconsistent with the high-pressure environment of actual engine combustion chambers. Furthermore, the perturbation excitation direction is single, making it impossible to reveal the changes in acoustic modal oscillation characteristics caused by different excitation directions. Summary of the Invention

[0006] The present invention aims to provide a wide-band pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation directions. This system is capable of axial, radial, and tangential pulse excitation, and offers a wide range of combustion chamber acoustic frequencies, a wide range of combustion chamber backpressures, and diverse atmospheres. These varying atmospheres influence acoustic oscillations by affecting the speed of sound.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] The 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 consists of seven parts: the igniter, the barrel, solid fuel, O-ring, brass diaphragm, brass diaphragm gasket, and barrel. The igniter, barrel, and barrel are all connected by threads. A brass diaphragm gasket compresses the brass diaphragm between the barrel and the barrel to create a primary seal, while the O-ring creates a secondary radial seal. The solid fuel is loaded into the barrel and ignites and burns due to the high temperature or electric spark generated by the igniter. The resulting high-temperature combustion gas increases the pressure inside the barrel, reaching the rupture pressure of the brass diaphragm, rupturing it. The high-pressure combustion gas forms a shock wave within the barrel that propagates downstream. The brass diaphragm is selected based on the required rupture pressure, while the solid fuel is selected based on practical constraints such as gas production rate, experimental cost, and safety.

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

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

[0012] The combustion chamber is mainly used to simulate the actual engine combustion chamber at the acoustic frequency. The axial length L, inner diameter a and other dimensions of the internal cavity are determined by the required acoustic characteristic frequency f. mnq The decision is calculated by the formula for calculating the acoustic frequency of the cylinder:

[0013]

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

[0015] The flange cover and chamber 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 chamber 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 varying dimensional parameters such as length L and inner diameter a, combustion chambers with different characteristic frequencies can be simulated. For a combustion chamber with a fixed length L and inner diameter a, by varying the radial, tangential, and longitudinal modal orders m, n, and q, a variety of modes with frequencies ranging from hundreds to thousands of Hz can be generated, enabling wide-band, multi-modal oscillation experiments. By introducing safety gases of varying 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 performed across a wide backpressure range of 0.1 to 25 MPa and in different atmospheres. 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 of the actual engine under two working conditions: the first is to fill the combustion chamber with safety gas to reach a certain pressure value, keep the intake and exhaust valves closed, which corresponds to the stable working 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 so that the pressure value gradually increases or decreases. At this time, it corresponds to the ignition boost or thrust adjustment state of the engine, and the chamber pressure undergoes 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 with frequency f, modal shape distribution with frequency f, and attenuation coefficient α of the mode with frequency f.

[0019] ① The pressure oscillation frequency f, the amplitude A of the mode with frequency f, and the modal shape distribution with 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 graph of the measuring point, and directly read the peak frequency f and the corresponding amplitude A from the graph; draw an image of the amplitude A-position at different measuring points to obtain the modal shape distribution with frequency f.

[0020] ② The attenuation coefficient α of the mode with frequency f is obtained by the following method: the pressure-time data of a certain measuring point in the combustion chamber are band-pass filtered near the frequency f, and the filtered curve is taken from t1 to t n The pressure peak 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 piezoelectric dynamic pressure sensors, piezoresistive dynamic pressure sensors, and static pressure sensors. The piezoelectric dynamic pressure sensor is used for real-time online measurement of dynamic pressure within the pulse gun, with a range of 0 to 100 MPa, an accuracy of 1% FS, and a natural frequency of up to 150 kHz. The piezoresistive dynamic pressure sensor has a range of 0 to 15 MPa or 0 to 25 MPa, an accuracy of 0.25% FS, and a resonant frequency of up to 461.6 kHz. The static pressure sensor has a range of 0 to 25 MPa and an accuracy of 0.25% FS.

[0024] The data acquisition system consists of a charge conditioner and a data acquisition instrument. The charge conditioner converts 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 four channels. The data acquisition instrument has 16 channels, collects data at a maximum sampling rate of 256kHz, and is connected to a computer via a gigabit network cable.

[0025] The disclosed variable-excitation-direction, wide-band pulse gun-combustion chamber acoustic oscillation experimental system operates as follows: Assemble and secure the combustion chamber to the experimental bench, connect the air lines, 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 the pressure test system is functioning 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 reaching the required back pressure.

[0027] When simulating the engine ignition boost or thrust adjustment state: adjust the opening of the intake and exhaust valves, introduce safety gas into the combustion chamber, observe the static pressure sensor reading, 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 system to trigger synchronous data acquisition. The solid fuel in the pulse gun ignites and burns, generating a large amount of high-temperature combustion gas, which rapidly increases the pressure inside the gun. Once the brass diaphragm reaches its rupture pressure, the diaphragm ruptures, and the high-pressure combustion gas forms a high-pressure pulse in the barrel and rapidly enters the combustion chamber, generating pulse excitation. The sensor array measures the dynamic pressure in real time, which is then collected by the data acquisition system. Once the readings from each pressure sensor stabilize, the data acquisition system terminates the data acquisition. The inlet valve is closed, and the exhaust valve is opened to exhaust the combustion chamber, concluding the broadband pulse gun-combustion chamber acoustic oscillation experiment.

[0029] Beneficial effects:

[0030] 1. The disclosed wide-band pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction, which fills the combustion chamber with safety gases of varying properties, such as nitrogen or argon, in a cold state, maintains backpressure at a fixed value between 0.1 and 25 MPa, simulating the chamber pressure environment of a stable engine operation. Furthermore, by controlling the openings of the intake and exhaust valves, the backpressure is dynamically varied within a range of 0.1 to 25 MPa, simulating the chamber pressure environment during engine ignition, boosting, or thrust regulation. This experimental system is therefore capable of simulating the combustion chamber pressure environment over a wide pressure range and in various atmospheres.

[0031] 2. The disclosed wide-band pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction, based on the principle that the simulated phenomena are essentially identical to the real phenomena, uses the same natural frequency as that of an actual engine combustion chamber to calculate the dimensional parameters of the experimental system's combustion chamber. Therefore, engine combustion chambers with different natural frequencies can be simulated simply by changing the relevant dimensional parameters. Axial, radial, and tangential pulse gun interfaces are simultaneously provided on the combustion chamber. Different pulse gun interfaces correspond to different pulse incidence directions, enabling the introduction of pulse excitation disturbances into the combustion chamber from the axial, radial, and tangential directions. This simultaneously excites different acoustic modes in the combustion chamber, corresponding to different oscillation frequencies. Therefore, this experimental system is capable of studying the acoustic oscillation characteristics of combustion chambers over a wide frequency range.

[0032] 3. The present invention discloses a wide-band pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction. The pulse gun uses the high-pressure combustion gas generated by the combustion of solid fuel to break through the brass diaphragm to form a pulse disturbance with a high pressure amplitude. The amplitude of the pulse disturbance is related to the amount of solid fuel used and the rupture pressure of the brass diaphragm. The quality of the solid fuel used 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 wide-frequency domain pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction disclosed in the present invention uses high-frequency, high-precision pressure sensors to measure the pressure dynamic process in the pulse gun and the combustion chamber. The pressure data of each measuring point can be obtained by conducting a single experiment. In the post-processing process, the performance parameters of the pulse gun and the acoustic characteristic parameters such as the frequency, amplitude, mode, and attenuation process of the pressure oscillation in the combustion chamber can be obtained based on these data. This is helpful to study the propagation and attenuation mechanism of the pressure disturbance in the combustion chamber and the formation process of different modal vibration modes of the pressure oscillation, which helps to improve the combustion stability of the pulse gun, and thereby improve the stability of the wide-frequency domain pulse gun-combustion chamber acoustic oscillation experiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the apparatus of the wide-frequency domain pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction disclosed in the present invention;

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

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

[0037] Figure 3 This is the structure diagram of the pulse gun;

[0038] Among them: 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 - barrel.

[0039] Figure 4 This is the combustion chamber structure diagram;

[0040] Among them: 2.1—flange cover, 2.2—cavity, 2.3—metal bolts and nuts. DETAILED DESCRIPTION

[0041] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0042] Example 1:

[0043] like Figure 1 As shown, the wide-band pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction disclosed in this example consists of a pulse gun 1, a combustion chamber 2, and a pressure test system 3. The pressure test 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 device.

[0044] The experimental system principle 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 simultaneously activates the ignition circuit and sends a trigger signal to the data acquisition device 3.5. The solid fuel 1.3 in the pulse gun 1 is ignited by the igniter 1.1, and data acquisition by the data acquisition device 3.5 begins. The combustion of the solid fuel 1.3 in the pulse gun 1 produces a large amount of high-temperature combustion gas, causing the pressure within the gun barrel 1.2 to rise rapidly. Upon reaching the rupture pressure of the brass diaphragm 1.5, the diaphragm 1.5 ruptures, and the high-temperature, high-pressure combustion gas forms a shock wave through the gun barrel 1.7 and enters the combustion chamber 2. This pulse excitation generates pressure oscillations that decay over time. Piezoelectric dynamic pressure sensor 3.1 measures pressure-time data at all points within pulse gun 1, outputting it in real-time as a charge signal to charge conditioner 3.3. Charge conditioner 3.3 converts the received charge signal into a voltage signal, which is then output to data acquisition device 3.5. Piezoresistive dynamic pressure sensor 3.2 measures pressure-time data at all points within combustion chamber 2, outputting it in real-time as a voltage signal to data acquisition device 3.5. Data acquisition device 3.5 connects to an external computer to store the measured data. Power is required for igniter 1.1, piezoresistive dynamic pressure sensor 3.2, charge conditioner 3.3, data acquisition device 3.5, and the computer in the experimental system.

[0045] As an optional method, the data acquisition method of the data acquisition device 3.5 can be changed to pressure triggering, that is, the acquisition starts when the static pressure sensor 3.4 reaches a specified pressure.

[0046] Pulse gun 1 Figure 3As shown, it consists of an igniter 1.1, a gun 1.2, a 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, and is provided with 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 stick the brass diaphragm 1.5 to the flat side of the brass diaphragm gasket 1.6; then place the side of the brass diaphragm gasket 1.6 with the conical protrusion into the conical countersunk hole of the barrel 1.7, and keep the barrel 1.7 upright; after placing 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 gasket 1.6 to achieve the first seal, and the O-ring is the second seal; finally, put the solid fuel 1.3 into the gun, install the igniter 1.1 and press the combination gasket. In the experiment, different types of brass diaphragms 1.5 and solid fuels 1.3 of different qualities 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 mounting threads are matched.

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

[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: the back pressure of the combustion chamber 2 is 6 MPa, the solid fuel 1.3 is 6 grams of black powder, the rupture pressure of the brass diaphragm 1.5 is 60 MPa, the pulse gun 1 is installed on the radial interface, three pressure measuring points are used on the pulse gun 1, four measuring points are used on the combustion chamber 2, and the data acquisition instrument 3.5 collects data for approximately 60 seconds from the time the ignition signal is sent.

[0050] This example discloses a wide-band 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 above assembly method and fix it to Figure 1On the experimental bench shown, the axial and tangential interfaces of the pulse gun 1 and the unused interface of the piezoresistive dynamic pressure sensor 3.2 are blocked with corresponding types of plugs.

[0052] Step 2: Connect the air inlet and exhaust valves and the corresponding gas pipelines, valves, gas cylinders, etc., keep the gas cylinders closed, the air inlet and exhaust valves open, and install the piezoresistive dynamic pressure sensor 3.2.

[0053] Step three: assemble the pulse gun 1 according to the above-mentioned assembly method, install it on the radial interface of the cavity 2.2, and 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 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, and 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. Ignitor 1.1 begins operating, and data acquisition device 3.5 begins collecting data. Solid fuel 1.3 ignites and burns intensely, producing a large amount of high-temperature combustion gas. This rapidly increases the pressure within gun barrel 1.2. When the pressure reaches approximately 60 MPa, brass diaphragm 1.5 ruptures, generating a high-pressure pulse. This pulse, along with the combustion gas, is ejected through barrel 1.7 into combustion chamber 2, inducing pressure oscillations.

[0056] Step 6: After the data acquisition instrument 3.5 has collected data for about 60 seconds, it is manually stopped and the exhaust valve is slowly opened to relieve the pressure and exhaust the entire system. The pulse excitation experiment under this working condition is completed.

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

[0058] Example 3:

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

[0060] The specific implementation steps of the broadband pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction disclosed in this example are as follows:

[0061] Step 1: Assemble the combustion chamber 2 according to the above assembly method and fix it to Figure 1 On the experimental bench shown, the axial and tangential interfaces of the pulse gun 1 and the unused interface of the piezoresistive dynamic pressure sensor 3.2 are blocked with corresponding types of plugs.

[0062] Step 2: Connect the air inlet and exhaust valves and the corresponding gas pipelines, valves, gas cylinders, etc., keep the gas cylinders closed, the air inlet and exhaust valves open, and install the piezoresistive dynamic pressure sensor 3.2.

[0063] Step three: assemble the pulse gun 1 according to the above-mentioned assembly method, install it on the radial interface of the cavity 2.2, and then install the piezoelectric dynamic pressure sensor 3.1 and the emergency pressure relief valve.

[0064] Step 4: Connect all circuits and signal cables, confirm that all sensor zero points and noise levels are correct, and adjust the data acquisition mode of 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 static pressure sensor 3.4 reaches 10 MPa, data acquisition is automatically triggered.

[0065] Step 5: After the collector 3.5 is triggered, the ignition switch is immediately turned on, and the igniter 1.1 begins operating. The solid fuel 1.3 ignites and burns violently, producing a large amount of high-temperature combustion gas, which rapidly increases the pressure within the gun barrel 1.2. When the pressure reaches approximately 90 MPa, the brass diaphragm 1.5 ruptures, generating a high-pressure pulse. This pulse, along with the combustion gas, is ejected through the gun barrel 1.7 into the combustion chamber 2, inducing pressure oscillations.

[0066] Step 6: When the real-time reading of the static pressure sensor 3.4 reaches 20 MPa, the intake valve is manually closed and the collection is stopped. The exhaust valve is slowly opened to relieve the pressure and exhaust the entire system. The pulse excitation experiment is completed under this working condition.

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

[0068] The above specific description further illustrates the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only the specific implementation process of the present invention, which is used to explain the present invention and is not used 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 in the scope of protection of the present invention.

Claims

1. A wide-band pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction, characterized by: Includes pulse gun, combustion chamber and pressure test system; The pulse gun's main structure includes an igniter, a gun barrel, solid fuel, an O-ring, a brass diaphragm, a brass diaphragm gasket, and a barrel. The igniter, gun barrel, and barrel are all connected by threads. A brass diaphragm gasket compresses the brass diaphragm between the gun barrel and the barrel to achieve the first seal, and an O-ring achieves the second radial seal. The solid fuel is loaded into the gun barrel and ignited and burned by the high temperature or electric spark generated by the igniter. The high-temperature gas generated increases the pressure in the gun barrel. When the rupture pressure is reached, the brass diaphragm ruptures, and the high-pressure gas forms a shock wave in the barrel that propagates downstream. The brass diaphragm is determined based on the required rupture pressure, while the solid fuel is determined based on the actual constraints. The main structure of the combustion chamber is divided into 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 test 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 the combustion chamber in real time online; The data acquisition system is used to collect pressure information measured by the sensor; The pressure sensor array includes a piezoelectric dynamic pressure sensor, a piezoresistive dynamic pressure sensor, and a static pressure sensor; The data acquisition system includes a charge conditioner and a data acquisition instrument.

2. The wide-band pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction according to claim 1, characterized in that: The performance of the pulse gun is described by the measured internal ballistic curve. The main parameters are: peak pressure p in the gun max The pressure inside the gun rises from 0 to p max The time required t p , the propagation speed of the shock wave in the barrel V S =δx / Δt, where δx is the distance between the two pressure measuring points in the barrel, and Δt is the time difference between the pressure peaks in the pressure-time curve of the two pressure measuring points in the barrel; The axial length L and inner diameter a of the internal cavity of the engine combustion chamber are determined by the required acoustic characteristic frequency f mnq The decision is calculated by the formula for calculating the acoustic frequency of the cylinder: Where: m is the angular mode number, which is a non-negative integer, m = 0, 1, 2, ..., indicating the number of sound pressure nodes in the circumferential direction; n is the radial mode number, which is a non-negative integer, n = 0, 1, 2, ..., indicating the number of sound pressure nodes in the radial direction; q is the angular mode number, which is a non-negative integer, q = 0, 1, 2, ..., indicating the number of sound pressure nodes in the axial direction; is the average sound velocity of the medium; β mn is the derivative of the Bessel function J′ m The nth positive root of (x) that satisfies J′ m (β mn )=0; The flange cover and the cavity are connected by metal bolts and nuts and sealed by axially pressing the O-ring; the flange cover is provided with an axial pulse gun interface, an air inlet interface and a static pressure sensor interface, and the cavity is provided with radial and tangential pulse gun interfaces, a dynamic pressure sensor interface and an exhaust interface.

3. The wide-band pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction according to claim 1, characterized in that: By installing the pulse gun on three different interfaces, different pulse excitation directions can be achieved; by changing the length L and inner diameter a dimensional parameters, the simulation of combustion chambers with different characteristic frequencies can be achieved; for a combustion chamber with a fixed length L and inner diameter a, by changing the radial, tangential and longitudinal modal orders m, n, q, a variety of 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 with a wide back pressure range of 0.1 to 25 MPa and different atmosphere environments can be achieved; safety gases include non-flammable or inert gases such as nitrogen, argon and carbon dioxide.

4. The wide-band pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction according to claim 3, characterized in that: The combustion chamber is used to simulate the chamber pressure environment under two working conditions of the engine: the first is to fill the combustion chamber with safety gas to reach a certain pressure value, keep the intake and exhaust valves closed, this corresponds to the stable working 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 so that the pressure value gradually increases or decreases. This corresponds to the ignition boost or thrust adjustment state of the engine, and the chamber pressure undergoes a dynamic change process.

5. The wide-band pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction according to claim 1, characterized in that: The acoustic oscillation characteristics of the combustion chamber are described by the following parameters: pressure oscillation frequency f, amplitude A of the mode with frequency f, modal shape distribution with frequency f, and attenuation coefficient α of the mode with frequency f; wherein: ① The pressure oscillation frequency f, the amplitude A of the mode with frequency f, and the modal shape distribution with frequency f are obtained by the following method: performing fast Fourier transform (FFT) on the pressure-time data of the measuring point to obtain the amplitude-frequency graph of the measuring point, and directly reading the peak frequency f and the corresponding amplitude A from the graph; plotting the amplitude A-position image at different measuring points to obtain the modal shape distribution with frequency f; ② The attenuation coefficient α of the mode with frequency f is obtained by the following method: the pressure-time data of a certain measuring point in the combustion chamber are band-pass filtered near the frequency f, and the filtered curve is taken from t1 to t n The pressure peak p1~p n , calculate α using the following formula:

6. The wide-band pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction according to claim 1, characterized in that: The piezoelectric dynamic pressure sensor is used for real-time online measurement of dynamic pressure inside the pulse gun, with a range of 0 to 100 MPa, an accuracy of 1% FS, and a natural frequency of up to 150 kHz; the piezoresistive dynamic pressure sensor has a range of 0 to 15 MPa or 0 to 25 MPa, an accuracy of 0.25% FS, and a resonant frequency of up to 461.6 kHz; the static pressure sensor has a range of 0 to 25 MPa and an accuracy of 0.25% FS.

7. The wide-band pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction according to 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 to facilitate data acquisition by the data acquisition instrument. It has a total of 4 channels; the data acquisition instrument has a total of 16 channels, collects data at a maximum sampling rate of 256kHz, and is connected to the computer via a gigabit network cable.

8. The wide-band pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction according to claim 2, characterized in that: The solid fuel is black powder and the brass diaphragm is the bursting disc.

9. The wide-band pulse gun-combustion chamber acoustic oscillation experimental system with variable excitation direction according to claim 1, 2, 3, 4, 5, 6, 7 or 8, characterized in that: Assemble and secure the combustion chamber to the test bench, connect the gas lines, 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 test 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 the engine ignition boost or thrust adjustment state: adjust the opening of the intake and exhaust valves, introduce safety gas into the combustion chamber, observe the static pressure sensor reading, and gradually increase or decrease the back pressure; The igniter power is turned on and ignited, and at the same time, a trigger signal is sent to the data acquisition instrument to trigger synchronous acquisition; the solid fuel in the pulse gun is ignited and burned, generating a large amount of high-temperature gas to rapidly increase the pressure in the gun. After reaching the rupture pressure of the brass diaphragm, the brass diaphragm ruptures, and the high-pressure gas forms a high-pressure pulse in the barrel and is quickly injected into the combustion chamber, forming a pulse excitation; the sensor array measures the dynamic pressure in real time and the data acquisition system collects it. After the readings of each pressure sensor stabilize, the acquisition ends, the intake valve is closed, the exhaust valve is opened, the gas in the combustion chamber is discharged, and the wide-band pulse gun-combustion chamber acoustic oscillation experiment ends.

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