System and method for measuring burning rate of solid propellant by line scanning camera shooting under high overload condition

Abstract

The invention relates to a system and a method for measuring the combustion speed of a solid propellant by using a line scanning camera shooting method under a high overload condition. The system comprises a high-pressure transparent window combustion chamber on a high-overload table, a reflective mirror, an imaging lens, a line scanning camera and a photoelectric slip ring. The optical fiber communication card is arranged under the high-overload platform; and the control and data acquisition and processing subsystem is arranged. Under the condition of high overload generated by rotation of the high-overload table, light generated by combustion of the solid propellant penetrates through the transparent window and is imaged on the line scanning camera in the center of the high-overload table after being reflected by the reflective mirror. The camera converts the optical signal into a voltage signal. The signals are finally collected by the control and data acquisition and processing subsystem through the optical fiber, the photoelectric slip ring and the optical fiber communication card. And the data of the camera is processed to obtain the instantaneous burning rate and the average burning rate of the solid propellant under the condition of high overload (1000g).

Description

Technical Field

[0001] The invention relates to a system and a method for measuring the burning speed of solid propellant by line scanning photography under high overload conditions, belonging to the field of energetic material combustion parameter measurement. Background Art

[0002] Solid propellants in rocket engines convert their chemical potential into the heat energy of high-temperature gases through the combustion process, and then convert the heat energy of high-temperature gases into kinetic energy for rocket flight through the nozzle. The combustion properties of solid propellants in rockets and missiles are one of their four major properties (energy properties, combustion properties, mechanical properties, and safety properties). The regulation of the propellant combustion process, the release of energy, the law of burning rate changes, and the stability of the combustion process are key issues in the application of propellants in rocket and missile weapons. Research on propellant combustion theory, combustion mechanism, combustion regulation, etc. is one of the core contents of the development of rocket and missile technology in the field of aerospace and national defense.

[0003] At present, the burning rate measurement methods of solid propellants mainly include the closed explosive device method, engine method, target line method, underwater acoustic emission method, ultrasonic method, microwave method, photoelectric method, high-speed photography method, and line scanning camera real-time burning rate measurement method.

[0004] The rocket engine method (Ashraf MA Elghafour et al., Fuel 227 (2018): 478–484) calculates the burning rate based on the pressure (P)-time (t) curve formed by the combustion of solid propellant in the engine and the charge size.

[0005] The closed explosive method (Brian A McDonald et al. Combustion and Flame. 161 (2014): 363–369: Kumar Ishitha, PA et al. Journal of propulsion and power Vol. 32, No. 5, September–October 2016: 1104-1109; Songqi Hu et al. Combustion Science and Technology 186: 1858–1888, 2014; Yu-Zhu Pan et al. Propellants Explos. Pyrotech. 2012, 37, 439–444) is based on the fact that when a propellant or gunpowder sample of known shape and size is burned in a closed explosive, the gas produced causes the pressure in the closed explosive to rise. At different moments in the combustion process, the pressure value in the container is different. Based on the experimentally measured P~t curve, the burning rate of the propellant at each moment is calculated through certain mathematical processing.

[0006] In the above two methods, the amount of samples used in the experiment is large, the test cost and safety risk are high, which is not convenient for scientific research; and the measured burning rate is the burning rate value indirectly obtained based on the P~t curve.

[0007] The target line method (Supriya Singh et al. Journal of Industrial and Engineering Chemistry. 27 (2015): 88–95; Manisha B et al., Combustion Science and Technology. 2018, VOL. 190, NO. 9: 1614–1629) is to drill holes at both ends of the effective recording length (100 mm to 150 mm) of the charge and insert the thermal fuse. When the flame burns to the position of the first fuse, the burning flame will melt the fuse and start timing; when it burns to the position of the second fuse, the timing ends. The average burning speed is calculated based on the effective recording length of the charge and the burning time. When the target line method is used to measure the burning rate of low burning rate (burning rate below 50mm / s) solid propellant, the test accuracy can meet the requirements; but for high burning rate solid propellant (above 100mm / s), due to the limitation of technical methods, the test error reaches more than 20%; for ultra-high burning rate solid propellant (burning rate up to 1000mm / s), the test error is even greater, so the target line method is only used to measure the burning rate of solid propellant with a burning rate less than 50mm / s. In addition, the target line method can only measure the average burning rate of the propellant, and cannot measure the instantaneous burning rate.

[0008] The underwater acoustic emission method (Wu Lingling et al., Proceedings of the 22nd Annual Conference of the Chinese Society of Astronautics on Solid Rocket Propulsion (Propellant Volume) 2005.10:236-239) is to put a certain length of propellant into a combustion chamber, and fill the combustion chamber with water at a certain temperature, and the water must cover the propellant to a certain height; then use nitrogen to flush to the specified experimental pressure, and ignite after the pressure is constant. The burning propellant emits a deflagration sound, which is transmitted to the combustion chamber wall through water, and is received by the acoustic sensor close to the outer wall of the combustion chamber and converted into an electrical signal. The signal is amplified and used to start and stop the timing device, and the burning rate is calculated according to the distance of the acoustic sensor and the burning time of the solid propellant. This method is limited by its own technical conditions and is not suitable for the determination of the burning rate of high-burning-rate solid propellants. It is only suitable for the determination of the burning rate of propellants with a burning rate lower than 125mm / s. In this method, the solid propellant burns in water, which changes the combustion environment and causes a certain deviation between the test value and the actual value. In addition, low-temperature testing below 0°C is not possible and the adjustable pressure range is limited. This method is also not easy to use for some propellants with a high aluminum content.

[0009] The ultrasonic method (Hayri Yaman et al. Fuel. 115 (2014): 794–803; R Jeenu et al. Journal of Propulsion and Power. Vol. 29 (1), 2013: 216-226) uses the reflection of ultrasound on the combustion interface to measure the burning rate of solid propellants. Under the conditions that the sound wave transmission speed of the solid propellant and the matching layer material and the thickness of the matching layer are known, by testing the interval time of the reflected wave on the burning surface of the solid propellant, the instantaneous remaining length of the solid propellant at different times can be calculated, and then the instantaneous burning rate and average burning rate of the solid propellant at different times can be calculated.

[0010] High-speed photography (Guan Yingzi et al., Solid Rocket Technology. 1998.03:75-78; Alexey V.Sergienko et al., Propellants Explos. Pyrotech. 2019, 44:217–223; Balusamy Kathiravan et al., Propellants Explos. Pyrotech. 2019, 44:1–11; Sarah Isert et al. Combustion and Flame 162 (2015):1821–1828) uses a high-speed camera to continuously shoot the combustion process and calculate the instantaneous combustion speed and average combustion speed based on the position of the combustion interface at different times. Traditional high-speed photography consumes a lot of photographic film, and the process of developing the film and processing the data is very complicated. It has now been gradually replaced by numerical photography.

[0011] The line scanning camera real-time burning rate determination method is a solid propellant burning rate determination method invented by Beijing Institute of Technology in the 1980s and has been upgraded and modified several times (Ma Qingyun et al., Acta Ordnance. 1985.07:26-31; Yang Rongjie et al., Propulsion Technology. 2000.02:86-88). It consists of a transparent window combustion chamber, a line scanning CCD camera, a data acquisition card and a computer, etc. Figure 1 . The line scan camera converts the combustion flame light signal transmitted from the transparent window into a voltage signal according to the set line scan frequency and exposure time, and the computer collects and stores these signals in real time. The voltage value slightly higher than the surface of the unburned charge is set as the "threshold value", and the data processing system converts the analog voltage signal into a "binarized" signal according to the set "threshold value". The voltage above the threshold value is set to 1, and the voltage below the threshold value is set to 0. The position where the voltage jumps from 0 to 1 is the position of the "combustion interface". Finally, the data processing system can give the change relationship of the "combustion interface" over time, and the instantaneous combustion rate and average combustion rate of the solid propellant can be calculated based on this change relationship.

[0012] The advantages of this system are: 1) The amount of experimental samples is small (about 1g or less), which reduces the experimental cost and improves the experimental safety. 2) Based on thousands of sets of data on the relationship between the combustion interface and time of solid propellant grains, it is possible to calculate the instantaneous burning rate of the grain at a certain point, as well as the average burning rate of a certain section of the grain; when calculating the average burning rate, the burning rate is obtained by linear fitting based on hundreds or even thousands of sets of data on the relationship between the combustion interface and time, and the data reliability is high. 3) It can realize the burning rate measurement of ultra-high burning rate solid propellants. Taking a line scanning camera with a line scanning frequency of 100kHz as an example, for ultra-high burning rate propellants with a grain height of 10mm and a burning rate of 1000mm / s, 1000 sets of valid data can also be obtained, thereby obtaining a reliable burning rate, which meets the needs of measuring the burning rate of ultra-high burning rate solid propellants. When the single energetic compound (powdered single oxidizer, single explosive) is pressed into a short column with a height of 5 mm using a mold, 500 sets of valid data can be obtained when the burning rate reaches 1000 mm / s, which can be used to study the combustion mechanism of each solid oxidizer component of solid propellant.

[0013] Currently, this system can only measure the burning rate of solid propellants under static conditions, but cannot measure the burning rate of solid propellants under overload conditions. Summary of the invention

[0014] The object of the present invention is to solve the problem of measuring the burning velocity of solid propellants under high overload conditions using line scanning photography.

[0015] The invention relates to a solid propellant burning speed measuring system and method based on line scanning camera method under high overload condition.

[0016] The general idea of ​​the present invention is to install the high-pressure transparent window combustion chamber, optical imaging device, line scanning camera and other devices of the existing system on a high-speed rotating platform (high overload platform), and use the overload force generated when the platform rotates to provide a high overload environment for the combustion of the propellant grain. However, there is currently no line scanning camera that can withstand high overload (1000g), so it is necessary to install the camera in the central low overload area on the high overload platform, which requires the design of an optical path to transmit the optical signal generated by the combustion of the propellant in the high overload area to the camera in the low overload area. In addition, the signal generated by the rotating camera needs to be transmitted to the control and data acquisition and processing subsystem in a stationary state, and an optoelectronic slip ring needs to be configured to transmit the signal.

[0017] like Figure 2 As shown, the test system includes a high-pressure transparent window combustion chamber, a reflector, an imaging lens, a line scan camera and a photoelectric slip ring installed on a high overload platform, as well as a fiber optic communication card, a control and data acquisition and processing subsystem under the high overload platform.

[0018] The flame light generated by the combustion of solid propellant in the high-pressure transparent window combustion chamber in the high overload area passes upward through the transparent window, is reflected by the reflector and propagates horizontally, and is focused by the imaging lens and imaged on the photosensitive array of the line scanning camera. The photosensitive array converts the optical signal into a voltage digital signal, which is output through the optical fiber. During the optical fiber transmission process of the signal, the rotating data signal is transmitted to the stationary optical fiber through the photoelectric slip ring, and then collected and stored by the data acquisition and processing subsystem through the optical fiber communication card.

[0019] After the combustion is completed, the collected data is processed. The light intensity in different areas of the combustion flame zone is different, and the intensity of the corresponding voltage signal generated is also different. The voltage signal corresponding to the unburned charge is the weakest, while the signal in the center of the flame is the strongest. The voltage value on each pixel is represented by a gray point of corresponding depth (0 is completely black, 255 is white, and 0 to 255 are different depths of gray), and a grayscale line can be obtained. All grayscale lines can be combined to obtain a grayscale image of the combustion process, such as Figure 3 shown.

[0020] A voltage value slightly higher than the unburned grain is set as the "threshold". Voltages above the threshold represent the burned area of ​​the propellant grain, and voltages below the threshold represent the unburned area of ​​the grain. The pixel corresponding to the threshold voltage is the position of the "combustion interface". Based on the position of the "combustion interface" obtained from each scan, the relationship between the interface and the number of scans can be plotted. Then, based on the imaging scale factor and the line scan time, the relationship between the height of the solid propellant grain and time can be converted, such as Figure 4 As shown. Based on this, the transient burning speed of the solid propellant and the average burning speed of the entire grain can be calculated. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Prior art line scanning camera real-time burning rate measurement system

[0022] Figure 2 Solid propellant line scanning camera burning rate measurement system under high overload conditions

[0023] Figure 3 Grayscale image of the propellant burning process

[0024] Figure 4 The relationship between the height and time of the combustion interface during the combustion process of the propellant grain

[0025] Figure 5 High pressure transparent window combustion chamber DETAILED DESCRIPTION

[0026] The present invention is described in detail below through implementation modes. It is necessary to point out that the following is only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. All equivalent changes made on the basis of the technical solution of this application fall within the scope of protection of the present invention.

[0027] (I) Implementation method of test system

[0028] 1) Design a high pressure transparent window combustion chamber suitable for use under high overload conditions. Figure 5 As shown in the figure, the combustion chamber consists of an autoclave body, a transparent window, an end cover, a powder column fixing frame, an ignition device, a pressurizing device, and inlet and outlet pipes and valves. The combustion chamber can be used at a pressure of 1 to 100 MPa. The combustion chamber is installed in the high overload area of ​​the high overload table turntable; when the high overload table rotates at high speed, the overload acceleration borne by the powder column in the combustion chamber is 1 to 1000g (1000 times the acceleration of gravity).

[0029] 2) Design a long working distance optical path consisting of a reflector, an imaging lens, and related fixtures. The reflector is installed directly above the transparent window of the combustion chamber, and the lens is installed at an appropriate position between the reflector and the line scan camera. The optical path design is based on the principle of clear imaging under dynamic conditions.

[0030] 3) Select a high-speed line scan camera: The line scan camera must have a sufficiently high resolution and line frequency; have a high photoelectric conversion rate for visible light, transmit data through optical fiber, and be able to withstand a certain overload. The line scan camera is installed in the center of the central axis (hollow) of the high overload platform. It has been verified by experiments that when the central axis rotates at a speed of 1000rpm (the overload at the corresponding drug column is greater than 1000g), the selected camera can work normally.

[0031] 4) Design a high-speed optoelectronic slip ring. The slip rings currently sold on the market cannot meet the data transmission requirements under the condition of 1000rpm. It is necessary to design and develop a special optoelectronic slip ring. According to experiments, the developed optoelectronic slip ring can ensure real-time data transmission when the camera works at a line frequency of 100kHz under the condition of 1000rpm. The slip ring is installed at the lower end of the central shaft, and its rotor rotates with the central shaft, while the stator is stationary.

[0032] 5) Prepare control and data acquisition and processing software: The software should be able to control the camera's line frequency and other operating parameters; be able to collect camera data in real time; be able to output experimental results in the form of grayscale images and "height-time" graphs of the propellant based on the collected data; be able to calculate the instantaneous burning rate and average burning rate of the propellant and output the results.

[0033] 6) System integration: Install the high-pressure transparent window combustion chamber, reflector, imaging lens, line scan camera, and optoelectronic slip ring at the designed position on the high overload platform; and integrate them with the static fiber optic communication card, control and data acquisition and processing subsystem under the high overload platform to form a complete solid propellant line scan camera burning rate measurement system under high overload conditions.

[0034] (II) Implementation plan of the test method

[0035] 1) Determine the proportional coefficient. Before the experiment, the proportional coefficient of the test system must be calibrated first, that is, the actual height represented by each pixel. A "calibration tube" is installed at the position where the propellant grain is placed in the combustion chamber. There are two slits at the upper and lower positions of the calibration tube; illuminate the slits, measure the pixel difference between the rising edges of the two slit light spots under clear imaging conditions, and calculate the proportional coefficient based on the distance between the slits on the calibration tube and the pixel difference.

[0036] 2) Install the solid propellant test sample on the grain rack in the high-pressure transparent window combustion chamber, seal the combustion chamber with the combustion chamber end cover, connect the pressurized air pipe, and start the pressurization program to pressurize the combustion chamber. When the pressure in the combustion chamber reaches the pressure required by the experiment, the pressurization process ends automatically. Close the air inlet valve and remove the pressurized air pipe.

[0037] 3) Start the high overload platform. When the high overload platform reaches the speed required by the set overload acceleration and the speed is stable, the control and data acquisition and processing subsystems enter the data acquisition state and ignite the solid propellant experimental charge.

[0038] 4) The flame light generated by the combustion of the solid propellant grain in the high-pressure transparent window combustion chamber passes upward through the transparent window, is reflected by the reflector and propagates horizontally, and is focused by the imaging lens and imaged on the photosensitive array of the line scan camera. The photosensitive array converts the optical signal into a voltage digital signal, which is output through the optical fiber.

[0039] 5) During the optical fiber transmission of the signal, the rotating optical fiber is connected to the stationary optical fiber through the optical slip ring, and then enters the data acquisition and processing subsystem through the optical fiber communication card. The data acquisition and processing subsystem collects and saves the data of each pixel on the photosensitive array in real time during each line of scanning, and records the time when each line of data is collected.

[0040] 6) After the solid propellant grains are burned, shut down the high overload platform. After the high overload platform stops, connect the exhaust pipe, open the exhaust valve, and discharge the combustion exhaust gas in the combustion chamber. After the exhaust gas is discharged, you can open the combustion chamber end cover, take out the grain holder, clean the combustion chamber, and prepare for the next experiment.

[0041] 7) Output grayscale image. The voltage value generated by each pixel on the line scan camera array is represented by gray dots of corresponding depth (0 is completely black, 255 is white, and grays of different depths are between 0 and 255). This will give a grayscale line. By combining all the grayscale lines, a grayscale image of the combustion process can be obtained. The grayscale image can be used to determine whether the combustion of the sample is stable. A straight line can also be drawn along the light and dark interface of the grayscale image, and its slope is the combustion speed.

[0042] 8) Set a voltage value slightly higher than that of the unburned propellant as the "threshold". The pixel corresponding to the threshold voltage is the "combustion interface". Based on the position of the "combustion interface" obtained in each scan, the relationship between the interface and the number of scans can be plotted, and then based on the imaging scale factor and the line scanning time, it can be converted into the relationship between the position H of the solid propellant propellant combustion interface and the time t. Based on this, the transient combustion speed of the solid propellant combustion is calculated, and the average burning speed is calculated by linear regression method.

Claims

1. A high overload solid propellant line scanning camera burning rate measurement system, characterized in that: The burning rate measurement system includes a high-pressure transparent window combustion chamber on a high overload platform, a reflector, an imaging lens, a line scan camera, a photoelectric slip ring, an optical fiber communication card under the high overload platform, and a control and data acquisition and processing subsystem; the control and data acquisition and processing subsystem processes the collected solid propellant combustion flame signal to obtain the instantaneous burning rate and average burning rate of the propellant.

2. The system according to claim 1, characterized in that: The combustion chamber includes a high-pressure autoclave body, a transparent window, an end cover, a charge column fixing frame, an ignition device, a pressurizing device, and inlet and outlet gas pipes and valves; the combustion chamber can be used at a pressure of 1 to 100 MPa.

3. The system according to claim 1, characterized in that: The combustion chamber is installed in the high overload area of ​​the high overload platform; when the high overload platform rotates, the overload borne by the propellant in the combustion chamber is 1 to 1000g (g is the acceleration of gravity).

4. The system according to claim 1, characterized in that: When the high overload platform reaches the speed required by the set overload acceleration and the speed is stable, the control and data acquisition and processing subsystem enters the data acquisition state and ignites the solid propellant test charge.

5. The system according to claim 1, characterized in that: The sample combustion flame light signal is transmitted to the line scan camera located in the center of the high overload stage through a long working distance optical path composed of a reflector, an imaging lens and related fixtures.

6. The system according to claim 1, characterized in that: The line scan camera converts the flame light signal into a voltage signal. The data generated by the camera is transmitted in real time to the control and data acquisition and processing subsystem through a data transmission system composed of optical fiber and optoelectronic slip ring.

7. The system according to claim 1, characterized in that: During the optical fiber transmission of the signal, the rotating optical fiber is connected to the stationary optical fiber through the optoelectronic slip ring, and then enters the control and data acquisition and processing subsystem through the optical fiber communication card.

8. The system according to claim 1, characterized in that: The control and data acquisition and processing subsystem processes the collected signals to obtain the grayscale image of propellant combustion, the height-time relationship curve of the grain combustion interface, the instantaneous burning rate and the average burning rate.

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