Method for measuring flame temperature of energetic material based on ion spectral lines with same characteristics

Abstract

The invention relates to a system and a method for determining combustion flame temperature and distribution of an energetic material based on a characteristic spectral line method. The test system comprises a high-pressure transparent window combustion chamber, a transverse slit, an imaging lens, a high-resolution spectrometer, a line scanning camera and a data acquisition and processing subsystem. Flame light generated by combustion of the energetic material in the high-pressure transparent window combustion chamber passes through the transparent window and is imaged at a light inlet of the high-resolution spectrometer through the transverse slit and the imaging lens; the spectrograph disperses flame polychromatic light, and two characteristic spectral lines are respectively received by the two line scanning cameras and are converted into electric signals; output signals of the camera are collected and processed by the computer. The temperature of each point of a certain cross section of the combustion flame can be obtained through each time of scanning of the camera. Along with downward movement of the combustion surface, transverse flame temperature distribution of each row is obtained in sequence, and then longitudinal temperature distribution of combustion flames is obtained.

Description

Technical Field

[0001] The invention relates to a method for measuring the flame temperature and distribution of an energetic material combustion flame, and belongs to the field of energetic material combustion parameter measurement. Background Art

[0002] Energetic materials are compounds or mixtures that contain explosive groups or oxidants and combustibles, can independently undergo chemical reactions and output energy, including explosives, propellants, and solid propellants. Among them, solid propellants and propellants release their chemical potential through the combustion process, converting it into high-temperature gas, which is further converted into the kinetic energy of rockets, missiles, and artillery shells.

[0003] The temperature and distribution of the combustion flame are important energy parameters of solid propellants, and are also one of the main parameters for characterizing flow field characteristics and solid rocket engine performance. Accurately measuring the combustion temperature and temperature distribution of solid propellants is of great significance for accurately establishing mathematical and physical models of solid propellant combustion, adjusting the propellant burning rate and burning rate pressure index, and optimizing the performance design of solid rocket engines.

[0004] The methods for measuring the flame temperature and distribution of energetic material combustion mainly include the pre-buried thermocouple temperature measurement method and the non-contact spectral temperature measurement method.

[0005] 1) Thermocouple method Sabadell et al. (AIAA Journal, 3(9), 2015) used thermocouples to measure the flame temperature and distribution of energetic materials. A micro thermocouple was embedded in the energetic material. When the energetic material burned, the thermocouple probe spatially sensed the temperature of the condensed phase, the combustion interface, the flame zone near the interface, and the flame center area in turn. The problems with this method are: first, the temperature gradient in the flame zone is very large. Although the thermocouple is very small, it still appears "very large" and cannot sense the fine changes in the combustion temperature field; second, the temperature measurement range of a single thermocouple is limited, and the measured temperature cannot be too high. When the temperature reaches above 3000K, it is difficult for the thermocouple material to continue to work in the flame; third, the thermocouple has a slow response speed to temperature and cannot keep up with the rapid changes in the displacement and temperature of the flame zone, so it is impossible to sense the real-time flame temperature; fourth, the embedded thermocouple changes the local structure of the condensed phase of the charge column, increases the heat transfer channel of the thermocouple wire to the interface, and affects the temperature distribution of the flow field in the flame zone. It is difficult to be consistent between the sensed flame temperature and the actual temperature.

[0006] 2) Optical / spectral temperature measurement method The optical / spectral temperature measurement method has the characteristics of non-contact measurement, fast measurement speed, wide temperature measurement range, ability to measure high temperature, wide spectral frequency range, and multiple spectral types. It has obvious advantages in measuring the flame temperature of energetic material combustion.

[0007] Phosphorescence thermography Bi Zhixian et al. (Experimental Fluid Mechanics 27(3), 2013) and Michael et al. (Journal of Propulsion and Power.36(5), 2020) used phosphorescence thermography to measure the combustion flame temperature. The phosphorescent material is sprayed on the surface of interest and excited by a light source of appropriate wavelength. The excited phosphorescent material will emit phosphorescence of different wavelengths. The phosphorescence luminescence process is detected and recorded. By analyzing its luminescence characteristics, a relationship can be established with the temperature. Phosphorescence thermography is generally used to measure the combustion wall temperature or the side surface temperature of the propellant column. If the flame temperature is to be measured, the phosphorescent substance must be added to the flame. This will change the structure of the flame, and there will be a certain gap between the measured temperature and the actual temperature.

[0008] Coherent anti-Stokes Raman Spectroscopy (CARS) Li Jinzhao (Harbin Institute of Technology thesis 2013) uses CARS technology to measure combustion temperature. The light emitted by the light source generates a beam of pump light and a beam of Stokes light after a series of optical devices. When the frequency difference (w1–w2) between the pump light (w1) and the Stokes light (w2) is equal to the Raman resonance frequency wR of the medium molecules, the intrinsic vibration or rotation of the medium molecules is resonantly enhanced. At this time, the detection light (w3) is incident, generating a CARS signal (w4) that is shifted to the high-frequency direction; the temperature of the detection area can be obtained based on the properties of the CARS light signal.

[0009] Planar Laser Induced Fluorescence (PLIF) Yongxu Lu (Dissertation, Southwest University of Science and Technology, 2022) Determine the combustion temperature of the propellant based on the two-color planar laser induced fluorescence technology. The laser is used to transition the particles in the flow field from the ground state to the excited state. The excited particles undergo a series of radiationless transitions back to the ground state, and the energy generated in the process is released in the form of fluorescence radiation. The corresponding temperature can be obtained by detecting and analyzing the fluorescent photons released by the particles.

[0010] Absorption spectroscopy Vanderhoff et al. (Applied Spectroscopy, 53(7), 1999; Propellant, Explosives and Pyrotehnics, 17(4), 1992; International Symposium on Combustion, July, 1992.) used laser light generated by a CO2 laser to irradiate the combustion flame zone and measured the dark zone temperature (1300-1500K) and the luminous zone temperature of the solid propellant combustion flame based on the absorption spectra of NH, CN, NO and OH.

[0011] FTIR absorption spectroscopy Mallery et al. (Combustion Science and Technology, 122, 1997) established a method for measuring the flame zone temperature of solid propellant combustion flames using FTIR absorption spectroscopy. A beam of FTIR light is passed through the combustion flame zone of the propellant, and the light transmitted by the flame is detected on the other side. The temperature of the flame zone is measured based on the absorption of light by the flame components.

[0012] The above-mentioned phosphorescent thermal imaging, coherent anti-Stokes Raman scattering, planar laser induced fluorescence, absorption spectroscopy and FTIR absorption spectroscopy devices must include a light source, so the system is relatively complex; and these methods must use a beam of light to illuminate the flame area when measuring temperature, applying light energy to the flame area, changing the original energy distribution, and may change the original combustion process, so the measured temperature may not be the actual flame temperature.

[0013] In the infrared thermal imaging method, the light emitted by the object to be measured is focused by the lens, split by the grating, and converted into an infrared detector (which converts the light signal into an electrical signal), and finally the electrical signal is converted into a thermal image. The wavelength used by common infrared thermal imagers is between 3 and 14 μm. Ke-Juan Menga et al. (Combustion and Flame. 237 (111855), 2022) used infrared thermal imaging technology to measure the combustion flame temperature of solid propellants. However, some gas components in the propellant combustion flame zone have strong absorption of infrared light, such as CO2 and H2O, which have strong absorption of the working band of infrared thermal imaging between 8 and 14 μ. Part of the infrared light is absorbed, reducing the original radiation intensity, resulting in a lower measured flame temperature. Because the CO2 concentration in the combustion products of different solid propellant formulas is different; even for the same formula, in different flame areas, due to different degrees of completeness of combustion, the CO2 conversion rate is different, and the CO2 concentration is also different. Therefore, the measurement error caused by gas absorption is still difficult to correct.

[0014] Dual-wavelength method Xu Chaoqi et al. (Solid Rocket Technology. 33(5), 2010) used the dual-wavelength method to test the combustion flame temperature of solid propellants. This method is based on Planck's law of blackbody radiation and assumes that the flame spectrum of energetic materials is a continuous spectrum. The light intensity of the two bands of 0.4-1.1μm and 0.9-1.7μm in the visible light region is used to test the combustion flame temperature of solid propellants.

[0015] Infrared thermal imaging and dual-wavelength methods use the light of the combustion flame for testing without external energy input. The theoretical basis of these technologies is the three laws of blackbody radiation, but the combustion flame spectrum of the propellant is composed of a continuous spectrum and a series of spectral lines emitted by specific particles, and the intensity of the spectral lines is much higher than the continuous spectrum (Yang Rongjie et al. Combustion and Flame. 145: 836-44, 2006; Journal of Thermophysics and Heat Transfer. 18 (3), 2004), so according to the blackbody or graybody assumption, a large error will be generated.

[0016] Characteristic spectral line temperature measurement method Yang Rongjie et al. (Combustion and Flame. 145: 836-44, 2006; Journal of Thermophysics and Heat Transfer. 18 (3), 2004; Spectroscopy and Spectral Analysis. 24 (10), 2004) proposed a method for measuring the combustion flame temperature of energetic materials based on the characteristic emission line of the solid propellant combustion flame. Theoretically, at a certain temperature T, the characteristic ion is in an excited state (with an energy of E u ) spontaneously transitions back to the ground state (with energy E l ), a spectral line of a specific frequency will be emitted. The relationship between the emission coefficient of this spectral line and the flame temperature is expressed as:

[0017]

[0018] Where: T is temperature (K)

[0019] v is the frequency of the spectral line

[0020] ε v is the emission coefficient of the spectral line with frequency v

[0021] A ul The probability that an excited electron spontaneously transitions back to the ground state

[0022] g u is the statistical weight of the excited state energy level

[0023] E u is the energy of the excited state (high potential energy)

[0024] N(T)u is the particle number density, that is, the number of particles in the excited state energy level per unit volume.

[0025] Z(T) is the normalization constant, also known as the partition function

[0026] k is the Boltzmann constant

[0027] h is Planck's constant

[0028] If the two characteristic spectral lines in the flame are emitted by the same ion, the ion number density and the partition function are the same. Therefore, the formulas for the two spectral lines can be related to obtain:

[0029]

[0030] As long as the excited state energy, transition probability and statistical weight of the two spectral lines are known, the flame temperature can be calculated based on the emission coefficients of the two spectral lines.

[0031] Based on the spectral characteristics of typical solid propellant combustion flames, Yang Rongjie et al. selected two characteristic spectral lines of nitrogen secondary ions (NII) at 624.241nm and 701.398nm respectively.

[0032] Test equipment see Figure 1 It consists of a combustion chamber, a transverse slit, a primary imaging lens, an optical rotating mirror scanner, a secondary imaging lens, a multi-channel small spectrometer, a phototube, a weak signal amplifier and a data acquisition and processing system.

[0033] The flame light generated by the combustion of energetic materials in the high-pressure transparent window combustion chamber passes through the transparent window, and is imaged on the reflective surface of the optical rotating mirror scanner through the transverse slit and the primary imaging lens; the optical rotating mirror scanner is a positive 16-faceted mirror column, and when it rotates to a certain specific angle, only the light from a certain point on the cross section of the burning flame is reflected and imaged to the light inlet of the multi-channel small spectrometer; the multi-channel small spectrometer disperses this complex light spot into two monochromatic light spots of specific wavelengths, and the two monochromatic light spots of specific wavelengths are respectively received by two phototubes and converted into electrical signals; the two electrical signals are amplified by the weak signal amplifier and then collected and stored by the computer.

[0034] When the optical rotating mirror scanner rotates at a fixed speed, the angle of the rotating mirror reflection surface changes successively, and the light from different points of the cross section of the burning flame is sent to the spectrometer successively, thus completing the horizontal scanning. According to the results of each horizontal scanning, the light intensity is converted into the emission coefficient through Abel transformation, and the temperature of each horizontal point of the burning flame can be calculated.

[0035] During the combustion process, the combustion interface and flame zone of the energetic material continuously move downward. With the displacement of the combustion interface and flame zone, the longitudinal flame temperature distribution of the combustion flame zone can be obtained based on the transverse flame temperatures of each row.

[0036] This technology uses the flame light for testing, does not require external light sources, and does not change the energy structure of the flame. It selects spectral lines based on the actual spectrum of the flame, and there is no problem of inconsistency between the basic assumptions and the actual spectrum. However, it uses an optical rotating mirror scanner to achieve lateral scanning of the flame, which has caused some problems:

[0037] 1) Vibration problem of the rotating mirror: The maximum rotation speed of the rotating mirror can reach 4000rpm. At this high speed, the system will inevitably vibrate, which will have a serious adverse effect on the stable transmission and conversion of the signal.

[0038] 2) Low temporal and spatial resolution: The rotating mirror is a 16-faceted mirror column. When rotating at 4000rpm, it can scan 1067 lines (about 1000 lines) per second, that is, 1 line is scanned in 1ms, and the temporal resolution is 1ms. This speed is acceptable for the test of low-burning-rate energetic materials, but it cannot meet the test of the flame temperature of high-burning-rate energetic materials. Assuming that the burning rate of the energetic material is 100mm / s, and the combustion interface moves down 100μm per millisecond, the longitudinal resolution is only 100μm. This cannot meet the requirements of the flame temperature and its distribution test for the flame zone with a high temperature gradient. Summary of the invention

[0039] The purpose of the present invention is to solve the problems of vibration generated when an optical rotating mirror scanner rotates and low resolution of the test system in a characteristic spectrum line method temperature measurement system in the prior art.

[0040] The invention relates to a system and method for measuring the temperature and distribution of a combustion flame of an energetic material based on the intensity of characteristic spectral lines of the same type of ions in the combustion flame.

[0041] The measurement system includes a high-pressure transparent window combustion chamber, a transverse slit, an imaging lens, a high-resolution spectrometer, a line scan camera, and a data acquisition and processing subsystem. Figure 2 .

[0042] The energetic material charge is installed at a fixed position in the high-pressure transparent window combustion chamber. The flame light generated after the ignition end of the charge is ignited passes through the transparent window, and is imaged at the light inlet of the high-resolution spectrometer through the transverse slit and the imaging lens. The spectrometer disperses this beam of complex light to form a spectrum. The monochromatic light of the two characteristic spectral lines of the same characteristic ions selected in the spectrum are received by two line scanning cameras respectively and converted into electrical signals. The output signal of the camera is collected and stored by a computer.

[0043] Each scan of the camera can obtain the light intensity of two characteristic spectral lines at each point of a cross section of the burning flame at a certain moment. After Abel transformation, the light intensity is converted into the emission coefficient, and the temperature of each point in the horizontal direction of the burning flame can be calculated by combining the electron transition probability, statistical weight and energy of the excited state energy level of the characteristic spectral line.

[0044] During the combustion process, the combustion interface and flame zone of the energetic material continuously move downward. With the displacement of the combustion interface and flame zone, the longitudinal flame temperature distribution of the combustion flame zone can be obtained based on the transverse flame temperatures of each row.

[0045] Compared with the existing characteristic spectrum temperature measurement system, the present invention has the following advantages:

[0046] 1) The system is simpler: the rotating mirror and its power supply and control system are eliminated, and the weak signal amplifier and its power supply are eliminated. The function of the rotating mirror is replaced by the horizontal scanning of the line scan camera. The line scan camera can have its own gain function, so the function of the weak signal amplifier can also be replaced by the line scan camera.

[0047] 2) The rotating mirror is eliminated, completely eliminating the influence of system vibration on the test results.

[0048] 3) Higher temporal and spatial resolutions. The line frequency of existing cameras reaches 115kHz, and the time for scanning a line is only 8.7μs; therefore, when the present invention uses a camera with this line frequency, the temporal resolution can reach 8.7μs. The pixel size of existing line scan cameras reaches 3.5μm×3.5μm, so when the present invention uses a camera of this specification for testing, the lateral spatial resolution can reach 3.5μm; when testing the combustion temperature distribution of energetic materials with a burning rate lower than 400mm / s (0.1μm / μs), the longitudinal spatial resolution can also reach 3.5μm; even when measuring the combustion flame temperature distribution of ultra-high burning rate energetic materials with a burning rate of 1000mm / s, its longitudinal spatial resolution can also reach 8.7μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 The existing characteristic spectrum method temperature measurement device system composition

[0050] 1. High-pressure transparent window combustion chamber, 2. Horizontal slit, 3. One-shot imaging lens,

[0051] 4. Optical rotating mirror scanner, 5. Secondary imaging lens, 6. Photoelectric tube

[0052] Figure 2 The test device system of the present invention is composed of DETAILED DESCRIPTION

[0053] 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.

[0054] (I) Implementation method of test system

[0055] 1) Design a high-pressure transparent window combustion chamber. The combustion chamber consists of a high-pressure autoclave body, a transparent window, a top cover, a charge column fixing frame, an ignition device, a pressurizing device, and an inlet and outlet pipe.

[0056] 2) Select appropriate characteristic spectral lines. Characteristic spectral lines are spectral lines produced by the transition of electrons in nitrogen ions, carbon ions or aluminum ions in flames between different energy levels. Early technologies used the wavelengths emitted by nitrogen II ions as The present invention can use this pair of spectral lines, or can use the wavelengths emitted by carbon II ions, which are respectively and The two spectral lines are taken as characteristic spectral lines or other suitable spectral lines.

[0057] 3) Design a high-resolution spectrometer based on the selected characteristic spectral lines: The spectrometer has a high enough resolution to ensure that the light of spectral lines other than the characteristic spectral lines cannot irradiate the pixels of the line scan camera. In addition, the two spectral lines generated after the dispersion of the complex light must be at a certain distance to ensure the installation space requirements of the line scan camera.

[0058] 4) Line scan camera selection: The line scan camera should have more than 4098 linear pixels; pixel size no larger than 3.5μm×3.5μm; line frequency higher than 115kHz; gain function; and high photoelectric conversion rate for characteristic spectral line light.

[0059] The two cameras should be able to work in sync using an external synchronizer.

[0060] 5) Prepare control and data processing software: The software should be able to control the camera's line frequency, exposure time, gain multiple and other operating parameters; be able to collect data from two cameras simultaneously in real time; be able to use Abel transformation to convert the collected light intensity into emission coefficient; be able to calculate the temperature of each light point; and report the lateral and longitudinal temperature distribution of the flame of the burning energetic material.

[0061] 6) System integration: The high-pressure transparent window combustion chamber, transverse slit, imaging lens, high-resolution spectrometer, line scan camera and data acquisition and processing subsystem are integrated into a complete energetic material combustion flame temperature and its distribution test system.

[0062] (II) Implementation plan of the test method

[0063] 1) The flame light generated by the combustion of energetic materials in the high-pressure transparent window combustion chamber passes through the transparent window, and is imaged at the light inlet of the high-resolution spectrometer through the transverse slit and the imaging lens; the spectrometer disperses this beam of complex light into a spectrum of single chromatographic lines.

[0064] 2) Two line scan cameras are installed at the positions corresponding to the two characteristic spectral lines at the output end of the spectrometer. The line scan cameras receive the light signals of the spectral lines and convert the light signals into voltage signals proportional to the light intensity. Each time the line scan camera scans, it can obtain the voltage signals corresponding to the light intensity of the two characteristic spectral lines at each point in the horizontal direction of the burning flame at a certain moment.

[0065] 3) The data acquisition and processing subsystem converts the voltage signal representing the light intensity into the emission coefficient of the spectral line through Abel transformation.

[0066] 4) According to the emission coefficient obtained from each scan data conversion, use the formula:

[0067]

[0068] Calculate the flame temperature at each horizontal point. The longitudinal temperature distribution of the flame is obtained based on the horizontal temperature of each row.

[0069] Where: ε v1 and ε v2 are the emission coefficients of the spectral lines with frequencies v1 and v2 respectively

[0070] A ul1 and A ul2 are the transition probabilities of the spectral lines with frequencies v1 and v2 respectively

[0071] g u1 and g u2 are the statistical weights of the spectral lines with frequencies v1 and v2 respectively

[0072] E u1 and E u2 are the high potential energies of the spectral lines with frequencies v1 and v2 respectively.

[0073] k is the Boltzmann constant

[0074] T is temperature (K)

[0075] The spectrum of the flame of energetic materials is very complex. For example, the wavelength of nitrogen II ions is There is another wavelength of the same energy level of nitrogen II ion near the spectral line. The spectral lines differ by only The wavelength of carbon II ions is There are also wavelengths of carbon II ions at the same energy level near the spectral line. and The first two lines differ by The difference between the last two The other wavelength for carbon II ions is There is also a carbon II ion with a wavelength of A spectrum line, they differ If we want to completely separate these spectral lines by improving the spectral resolution of the spectrometer, the spectrometer will inevitably become complex, bulky, and expensive. If several adjacent spectral lines with similar wavelengths are produced by the same ion and the same high-potential energy electronic level transition, the adjacent spectral lines can be combined into one spectral line for use.

[0076] For example, the wavelengths for carbon II ions are and The three spectral lines are numbered 1, 2 and 3; the wavelength is and The two spectral lines are numbered as spectral lines 4 and 5. According to the emission coefficient formula:

[0077]

[0078] The sum of the emission coefficients of the three spectral lines is:

[0079]

[0080] The sum of the emission coefficients of the two spectral lines is:

[0081]

[0082] but:

[0083]

[0084] In this way, the flame temperature can be calculated by measuring the total light intensity of characteristic spectral lines 1, 2, and 3 and the total light intensity of characteristic spectral lines 4 and 5 respectively.

[0085] In most literature, the dimensionless oscillator strength f is given as ul , instead of the transition probability A ul ,

[0086]

[0087] Use f ul Replacement Transition Probability A ul , then the temperature calculation formula becomes:

[0088]

[0089] or

[0090]

Claims

1. A system for measuring the flame temperature and its distribution of energetic material high pressure combustion based on the same characteristic ion spectrum method, characterized in that: The system includes a high-pressure transparent window combustion chamber, a transverse slit, an imaging lens, a high-resolution spectrometer, a line scan camera and a data acquisition and processing subsystem.

2. The system according to claim 1, characterized in that: The characteristic ion can be a nitrogen II ion, a carbon II ion or an aluminum ion; the same characteristic ion used has electron transitions at different high energy levels to produce two characteristic ion spectral lines, each of which can be a single spectral line or a spectral line formed by merging several adjacent spectral lines produced by electron transitions at the same high energy level.

3. The system according to claim 1, characterized in that: The high-resolution spectrometer needs to have a sufficiently high spectral resolution to ensure that light from spectral lines other than the characteristic ion spectral line cannot irradiate the pixels of the line scan camera.

4. The system according to claim 1, characterized in that: The two characteristic ion spectral lines generated after the combustion flame complex light is dispersed by the high-resolution spectrometer are at a certain distance to ensure the installation space requirements of the line scan camera.

5. The system according to claim 1, characterized in that: There are two line scanning cameras, which respectively collect light signals of two identical characteristic ion spectral lines output by the high-resolution spectrometer and perform photoelectric conversion. The two line scanning cameras controlled by an external synchronizer perform synchronous scanning.

6. A method for measuring the flame temperature and its distribution of high-pressure combustion of energetic materials based on characteristic ion spectrum method, characterized in that: The flame light generated by the combustion of the energetic material in the high-pressure transparent window combustion chamber passes through the transparent window, and is imaged at the light inlet of the high-resolution spectrometer through the transverse slit and the imaging lens; the high-resolution spectrometer disperses the complex light of the solid propellant combustion flame to obtain two characteristic ion spectral lines, and the monochromatic light of the two characteristic ion spectral lines is received by the line scanning camera and converted into electrical signals, and the electrical signals are collected and processed by the data acquisition and processing subsystem, so as to obtain the flame temperature and distribution of the energetic material combustion flame.

7. The method according to claim 6, characterized in that: The transverse slit selects a transverse light signal, the imaging lens focuses the light signal, and the high-resolution spectrometer disperses the complex light signal into a monochromatic light signal.

8. The method according to claim 6, characterized in that: Each scan of the line scan camera can obtain the light intensity of two characteristic ion spectral lines at each point of a certain cross section of the combustion flame. After Abel transformation, the light intensity is converted into an emission coefficient, and the temperature of each horizontal point of the combustion flame can be calculated.

9. The method according to claim 6, characterized in that: During the combustion process, as the combustion surface of the energetic material continues to move downward, the light passing through the transverse slit will gradually move away from the combustion interface of the solid propellant grain. The longitudinal temperature distribution of the combustion flame can be obtained based on the transverse flame temperature of each row.

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