Two-dimensional measurement method for temperature of combustion field

Abstract

The invention provides a two-dimensional measurement method for the temperature of a combustion field, which comprises the following steps: tuning laser frequency to be stabilized in the center of an iodine molecule absorption line, outputting a narrow-linewidth single-longitudinal-mode continuous light beam by a laser, dividing the light beam into two light beams by a spectroscope, enabling one light beam to pass through a reference light path and be used for acquiring an instrument function of a VIPA-based spectrograph, and enabling the other light beam to pass through a reference light path; the other beam of light is incident into a combustion field as exciting light and interacts with gas in the combustion field to generate a scattering signal, the light receiving system collects and filters the scattering signal to obtain filtered Rayleigh-Brillouin scattering (FRBS), and the filtered Rayleigh-Brillouin scattering (FRBS) is transmitted to the spectrograph and the CCD through the optical fiber for spectral resolution and signal acquisition. The scanning system completes two-dimensional profile scanning of a combustion field, retrieves the temperature of an acquired FRBS spectral line through an FRBS theoretical model, and achieves two-position measurement of the temperature of the combustion field. The method can be provided for retrieving the gas temperature based on FRBS in a high-temperature environment containing strong mie scattering or strong background light, can adapt to different environments and requirements, and provides higher flexibility.

Description

Technical Field

[0001] The present invention relates to the field of laser radar technology, and in particular to a two-dimensional measurement method for combustion field temperature. Background Art

[0002] The combustion field test conditions are very harsh, including the limited space test distribution and the strong stray light interference introduced by the limited space. These factors make the temperature measurement of the combustion field very difficult, and there is an urgent need for combustion field temperature technology with fast response speed, no interference with the flow field, high temporal and spatial resolution, high sensitivity and the ability to eliminate stray light interference.

[0003] In the prior art, Rayleigh-Brillouin scattering (RBS) technology uses the Tenti S6 model to fit the collected spectrum, with pressure, scattering angle, bulk viscosity, shear viscosity, thermal conductivity and internal specific heat capacity as known quantities of the Tenti S6 model, and temperature as the only variable to seek the best fitting value to retrieve the temperature. However, in the environment of strong Mie scattering and strong background light (such as combustion field), the RBS signal related to temperature information is relatively weak and can be easily covered by Mie scattering or background light, which brings great difficulties to the analysis of experimental results. Traditional filtered Rayleigh scattering technology (FRS) detects spectral energy and needs to introduce the FRS signal intensity under a known environment as a reference. The relative temperature curve is calibrated by measuring the intensity ratio to obtain the temperature of the combustion field, and absolute temperature cannot be measured. Summary of the invention

[0004] In view of the above technical problems, the present invention proposes a two-dimensional measurement method for combustion field temperature, which can filter out the interference of Mie scattering and background light on RBS signals, and realize direct measurement and two-dimensional profile scanning of combustion field temperature.

[0005] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a two-dimensional measurement method of the combustion field temperature, the laser frequency is tuned and stabilized at the center of the iodine molecule absorption line, the laser outputs a narrow line width single longitudinal mode continuous light beam, the light beam is divided into two beams by a spectroscope, one of which is passed through a reference optical path and is used to obtain the instrument function of a spectrometer based on VIPA, and the other beam is used as an excitation light to be incident on the combustion field through a first reflector and a second reflector in sequence, and interacts with the combustion field gas to generate a scattering signal; the light receiving system collects and filters the scattering signal to obtain filtered Rayleigh-Brillouin scattering (FRBS), which is transmitted to the spectrometer and CCD via optical fiber for spectral resolution and signal acquisition, the scanning system completes the two-dimensional profile scanning of the combustion field, and the collected data is saved to a computer for subsequent data processing, and the temperature of the collected FRBS spectrum line is retrieved through the FRBS theoretical model.

[0006] Furthermore, the scanning system includes an xz-axis high-precision electric translation stage and a controller, and the controller outputs a Tx signal and a Tz signal. The Tx signal controls the first slider to move along the x direction, thereby realizing synchronous scanning of the first reflector, the second reflector and the light receiving system in the x direction; the Tz signal controls the second slider to move along the z direction, thereby realizing synchronous scanning of the second reflector and the light receiving system in the z direction. The two-dimensional scanning measurement of the combustion field temperature is realized by controlling the Tx and Tz signals.

[0007] Furthermore, the light collecting system is composed of a circular wedge prism, a long focal length lens, a filtering system, a second focusing lens and a second optical fiber flange arranged in sequence. The filtering system includes a filter and an iodine molecule absorption cell. The filter is a narrow-band filter used to filter out stray light in other bands, and the iodine molecule absorption cell is used to filter out Mie scattering and background light.

[0008] Furthermore, the reference optical path is composed of an attenuation plate, a first focusing lens and a first optical fiber flange arranged in sequence.

[0009] The two-dimensional measurement method of the combustion field temperature of the present invention comprises the following steps: tuning the laser frequency to be stable at the center of the iodine molecule absorption line, the light emitted by the laser reacts with the combustion field gas to generate a scattering signal, an xz axis translation stage performs a two-dimensional scanning on the combustion field, an iodine molecule absorption cell in a light receiving system is used to filter out strong Mie scattering and background light, and the obtained filtered Rayleigh-Brillouin scattering (FRBS) signal is spectrally resolved and signal collected by a spectrometer based on VIPA and a CCD, and is saved in a computer for data processing; a transmittance function of the iodine molecule absorption cell is added to the Tenti S6 model to obtain a FRBS model, the collected FRBS spectral lines are fitted by the least squares method, and the temperature is retrieved by seeking the best fitting value with temperature as the only variable.

[0010] The two-dimensional measurement method of the combustion field temperature of the present invention uses an iodine molecule absorption cell to filter out strong Mie scattering and strong background light; uses a FRBS theoretical model to achieve absolute measurement of temperature; and uses a two-dimensional scanning system to achieve measurement of the two-dimensional profile of the combustion field. The present invention can provide a method for retrieving gas temperature based on FRBS in a high-temperature environment with strong Mie scattering or strong background light, can adapt to different environments and needs, and provide greater flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a schematic diagram of the absorption spectrum of iodine molecules near 532nm of the present invention; Figure 2 It is a schematic diagram of the overall structure of the present invention; Figure 3 This is a schematic diagram of filtering Rayleigh-Brillouin scattering signals according to the present invention; In the figure: 1-laser; 2-beam splitter, 3-reference light path, 4-attenuation plate, 5-first focusing lens, 6-first optical fiber flange, 7-spectrometer, 8-CCD, 9-computer; 10-xz axis high-precision electric translation stage, 11-controller, 12-first slider, 13-first reflector, 14-second slider, 15-second reflector, 16-combustion field, 17-light collecting system, 18-circular wedge prism, 19-long focal length lens, 20-filtering system, 21-filter, 22-iodine molecule absorption cell, 23-second focusing lens, 24-second optical fiber flange. DETAILED DESCRIPTION

[0012] See also Figure 1-Figure 3 The present invention discloses a two-dimensional measurement method for combustion field temperature. The laser frequency is tuned and stabilized at the center of the iodine molecule absorption line. The laser 1 outputs a narrow line width single longitudinal mode continuous light beam, which is divided into two beams by a spectroscope 2. One beam of light is used to obtain the instrument function of a spectrometer 7 based on VIPA via a reference optical path 3. The other beam of light is incident on a combustion field 16 as an excitation light via a first reflector 13 and a second reflector 15 in sequence, and interacts with the combustion field gas to generate a scattering signal. A light collecting system 17 collects and filters the scattering signal to obtain filtered Rayleigh-Brillouin scattering (FRBS), which is transmitted to a spectrometer 7 and a CCD 8 via an optical fiber for spectral resolution and signal acquisition. A scanning system completes a two-dimensional profile scan of the combustion field, and the collected data is saved in a computer 9 for subsequent data processing. The collected FRBS spectrum line is retrieved for temperature through a FRBS theoretical model.

[0013] Among them, there are many ultra-fine absorption structures in the absorption spectrum of iodine molecules in the visible band. There are 8 main Doppler broadened absorption lines near 532nm, i.e. 18786-18789 (such as Figure 1 As shown). Among them, the absorption depression of the iodine molecule 1109 line is wider than the spectrum of Mie scattering, but narrower than the spectrum of Rayleigh scattering; the transmittance of the absorption depression is low enough, while the transmittance on both sides is relatively high, so a high extinction ratio can be obtained; the slope of the absorption depression is steep and the sensitivity is good; the spacing between adjacent absorption lines is wide. In summary, the present invention selects the iodine molecule 1109 line as the absorption line for filtering out Mie scattering and background light. The two-dimensional measurement method of the combustion field temperature of the present invention can filter out the interference of Mie scattering and background light on the Rayleigh-Brillouin scattering (RBS) signal, and realize the direct measurement of the combustion field temperature and two-dimensional profile scanning.

[0014] Wherein, the VIPA-based spectrometer can realize rapid measurement of the spectrum.

[0015] Furthermore, the scanning system includes an xz-axis high-precision electric translation stage 10 and a controller 11, and the controller 11 outputs a Tx signal and a Tz signal. The Tx signal controls the first slider 12 to move along the x direction, thereby realizing synchronous scanning of the first reflector 13, the second reflector 15 and the light receiving system 17 in the x direction; the Tz signal controls the second slider 14 to move along the z direction, thereby realizing synchronous scanning of the second reflector 15 and the light receiving system 17 in the z direction. The two-dimensional scanning measurement of the temperature of the combustion field 16 is realized by controlling the Tx and Tz signals.

[0016] Furthermore, the light receiving system 17 is composed of a circular wedge prism 18, a long focal length lens 19, a filtering system 20, a second focusing lens 23 and a second optical fiber flange 24 arranged in sequence. The backscattered light is adjusted by the circular wedge prism to make the scattered light approximately parallel to the light receiving axis. The scattered light is collimated into an approximately parallel light beam by the long focal length lens. The filtering system filters out Mie scattering, background light and stray light of other wavelengths. The second focusing lens couples the scattered light transmitted in space into the second optical fiber flange. The filtering system 20 includes a filter 21 and an iodine molecule absorption cell 22. The filter 21 is a narrowband filter used to filter out stray light of other wavelengths. The iodine molecule absorption cell 22 is used to filter out Mie scattering and background light.

[0017] Furthermore, the reference optical path is composed of an attenuation plate 4, a first focusing lens 5 and a first optical fiber flange 6 arranged in sequence.

[0018] Furthermore, the FRBS theoretical model is based on the following formula: The Tenti S6 model is currently an effective method for describing RBS spectral lines. The experimentally measured RBS spectral lines are the result of the convolution of the ideal RBS spectral lines and the system instrument function. However, since the collected spectrum contains a narrow-band spectral structure composed of Mie scattering and background light, the iodine molecule transmittance function is added to the Tenti S6 model. , the obtained FRBS signal can be expressed as: ; In the formula, is the convolution operator; for The corresponding intensity; It is the RBS spectrum line normalized according to the Tenti S6 model and is related to the flow field state; is the instrument function of the VIPA-based spectrometer.

[0019] Furthermore, the temperature of the collected FRBS spectrum is retrieved by using the FRBS theoretical model, with pressure , scattering angle , molecular weight , volume viscosity , shear viscosity , thermal conductivity and internal specific heat The known quantity is temperature. The FRBS spectrum is fitted by least squares method. When the fitting residual is the smallest, the obtained temperature is considered to be the temperature corresponding to the detection spectrum. Determined by the circular wedge prism, it can be adjusted according to the experimental conditions. , volume viscosity , shear viscosity , thermal conductivity and internal specific heat It is obtained by querying the relevant database based on the gas composition of the combustion field.

[0020] Furthermore, the combustion field may be a detection object generated in different usage scenarios, including but not limited to: a gas combustion field in experimental research; engine exhaust and tail flame combustion status in the aviation field; and a high-temperature combustion field in the industrial field.

[0021] Specifically, the present invention provides a two-dimensional measurement method for the temperature of a combustion field. The laser frequency is tuned and stabilized at the center of the absorption line of the iodine molecule 1109. The laser 1 outputs a narrow linewidth single longitudinal mode continuous light beam, which is divided into two beams by a spectroscope 2. One beam passes through an attenuation plate 4, a first focusing lens 5 and a first optical fiber flange 6 to obtain an instrument function of a VIPA-based spectrometer 7, and the other beam is used as an excitation light and is incident on a combustion field 16 through a first reflector 13 and a second reflector 15 in sequence, and interacts with the combustion field 16 to generate a scattering signal.

[0022] The controller 11 controls the xz-axis high-precision electric translation stage 10 and outputs T x Signal and T z Signal, by T x The signal controls the first slider 12 to move along the x direction, realizing the synchronous scanning of the first reflector 13, the second reflector 15 and the light receiving system 17 in the x direction. z The signal controls the second slider 14 to move along the z direction, thereby realizing synchronous scanning of the second reflector 14 and the light collecting system 17 in the z direction, and realizing two-dimensional scanning measurement of the temperature field by controlling the Tx and Tz signals.

[0023] The backscattered light is adjusted in angle by a circular wedge prism 18 so that the scattered light is approximately parallel to the light-collecting axis. The scattered light is collimated into an approximately parallel light beam by a long focal length lens 19. The stray light of other bands is filtered out by a 532nm±0.5nm narrow-band filter 21. The background light and Mie scattering are filtered out by an iodine molecule absorption cell 22. The scattered light transmitted in space is coupled into a second optical fiber flange 24 by a second focusing lens 23 and transmitted to a spectrometer 7 and a CCD 8 by an optical fiber for spectral resolution and signal acquisition. The collected data is stored in a computer 9 for subsequent data processing.

[0024] The two-dimensional measurement method of the combustion field temperature of the present invention comprises the following steps: tuning the laser frequency to be stable at the center of the iodine molecule absorption line, the light emitted by the laser reacts with the combustion field gas to generate a scattering signal, an xz axis translation stage performs a two-dimensional scanning on the combustion field, an iodine molecule absorption cell in a light receiving system is used to filter out strong Mie scattering and background light, and the obtained filtered Rayleigh-Brillouin scattering (FRBS) signal is spectrally resolved and signal collected by a spectrometer based on VIPA and a CCD, and is saved in a computer for data processing; a transmittance function of the iodine molecule absorption cell is added to the Tenti S6 model to obtain a FRBS model, the collected FRBS spectral lines are fitted by the least squares method, and the temperature is retrieved by seeking the best fitting value with temperature as the only variable.

[0025] The two-dimensional measurement method of the combustion field temperature of the present invention uses an iodine molecule absorption cell to filter out strong Mie scattering and strong background light; uses a FRBS theoretical model to achieve absolute measurement of temperature; and uses a two-dimensional scanning system to achieve measurement of the two-dimensional profile of the combustion field. The present invention can provide a method for retrieving gas temperature based on FRBS in a high-temperature environment with strong Mie scattering or strong background light, can adapt to different environments and needs, and provide greater flexibility.

[0026] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not limited to the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A two-dimensional measurement method for combustion field temperature, characterized in that: The frequency of the laser is tuned and stabilized at the center of the iodine molecule absorption line. The laser (1) outputs a narrow line width single longitudinal mode continuous light beam, which is divided into two beams by a beam splitter (2). One beam passes through a reference optical path (3) and is used to obtain an instrument function of a VIPA-based spectrometer (7). The other beam is incident on a combustion field (16) as an excitation light through a first reflector (13) and a second reflector (15) in sequence, and interacts with the combustion field gas to generate a scattering signal. The light receiving system (17) collects and filters the scattering signal to obtain filtered Rayleigh-Brillouin scattering (FRBS), which is transmitted to the spectrometer (7) and CCD (8) via an optical fiber for spectral resolution and signal acquisition. The scanning system completes a two-dimensional profile scan of the combustion field, and the collected data is saved in a computer (9) for subsequent data processing. The collected FRBS spectrum line is retrieved for temperature through a FRBS theoretical model. The FRBS signal can be expressed as: ； In the formula, is the convolution operator; for The corresponding intensity; It is the RBS spectrum line normalized according to the Tenti S6 model and is related to the flow field state; is the instrument function of the VIPA-based spectrometer; The temperature of the collected FRBS spectrum is retrieved by using the FRBS theoretical model, with pressure , scattering angle , molecular weight , volume viscosity , shear viscosity , thermal conductivity and internal specific heat The known quantity is temperature. The FRBS spectrum is fitted by least squares method. When the fitting residual is the smallest, the obtained temperature is considered to be the temperature corresponding to the detection spectrum. Determined by the circular wedge prism, it can be adjusted according to the experimental conditions. , volume viscosity , shear viscosity , thermal conductivity and internal specific heat It is obtained by querying the relevant database based on the gas composition of the combustion field.

2. A two-dimensional measurement method of combustion field temperature according to claim 1, characterized in that: The scanning system comprises an xz-axis high-precision electric translation stage (10) and a controller (11). The controller (11) outputs a Tx signal and a Tz signal. The Tx signal controls the first slider (12) to move along the x direction, thereby realizing synchronous scanning of the first reflector (13), the second reflector (15) and the light collecting system (17) in the x direction. The Tz signal controls the second slider (14) to move along the z direction, thereby realizing synchronous scanning of the second reflector (15) and the light collecting system (17) in the z direction. By controlling the Tx and Tz signals, two-dimensional scanning measurement of the temperature of the combustion field (16) is realized.

3. A two-dimensional measurement method of combustion field temperature according to claim 1, characterized in that: The light collecting system (17) is composed of a circular wedge prism (18), a long focal length lens (19), a filter system (20), a second focusing lens (23), and a second optical fiber flange (24) arranged in sequence. The filter system (20) comprises a filter (21) and an iodine molecule absorption cell (22). The filter (21) is a narrow-band filter. The filter (21) is used to filter out stray light in other wavelength bands. The iodine molecule absorption cell (22) is used to filter out Mie scattering and background light.

4. A two-dimensional measurement method of combustion field temperature according to claim 1, characterized in that: The reference optical path (3) is composed of an attenuation plate (4), a first focusing lens (5) and a first optical fiber flange (6) which are arranged in sequence.

Images