A two-dimensional measurement method for combustion field temperature

Abstract

This invention provides a two-dimensional measurement method for combustion field temperature. The laser frequency is tuned and stabilized at the center of an iodine molecular absorption line. The laser outputs a narrow-linewidth, single-longitudinal-mode continuous beam. This beam is split into two beams by a spectroscope. One beam travels through a reference optical path and is used to obtain the instrument function of a VIPA-based spectrometer. The other beam, acting as excitation light, is incident on the combustion field, where it interacts with the combustion gas to generate a scattered signal. A light collection system collects and filters the scattered signal to produce filtered Rayleigh-Brillouin scattering (FRBS), which is then transmitted via optical fiber to a spectrometer and CCD for spectral resolution and signal acquisition. A scanning system completes a two-dimensional profile scan of the combustion field. Using the FRBS theoretical model, the collected FRBS spectral lines are used to retrieve the temperature, achieving two-dimensional measurement of the combustion field temperature. This invention provides a method for retrieval of gas temperature based on FRBS in high-temperature environments with strong Mie scattering or background light, adapting to diverse environments and needs, offering greater 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] Combustion field testing conditions are extremely demanding, including the confined test space and the strong stray light interference introduced by the confined space. These factors make combustion field temperature measurement very difficult, and there is an urgent need for combustion field temperature technology that has fast response speed, does not interfere with the flow field, has high temporal and spatial resolution, high sensitivity, and can eliminate stray light interference.

[0003] In existing technologies, Rayleigh-Brillouin scattering (RBS) technology uses the Tenti S6 model to fit the collected spectra. Pressure, scattering angle, bulk viscosity, shear viscosity, thermal conductivity, and internal specific heat capacity are used as known quantities in the Tenti S6 model, and temperature is used as the only variable to seek the best fitting value to retrieve the temperature. However, in environments with strong Mie scattering and strong background light (such as combustion fields), the RBS signal related to temperature information is relatively weak and can easily be obscured by Mie scattering or background light, which greatly complicates the analysis of experimental results. Traditional filtered Rayleigh scattering (FRS) technology detects spectral energy and requires the introduction of the FRS signal intensity in 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, but absolute temperature cannot be measured. Summary of the Invention

[0004] In response to 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] To achieve the above objectives, the present invention adopts the following technical solutions: a two-dimensional measurement method for the combustion field temperature, in which the laser frequency is tuned and stabilized at the center of the iodine molecule absorption line, and the laser outputs a narrow-linewidth single-longitudinal-mode continuous light beam, which is split into two beams by a spectrometer. One beam passes through a reference optical path and is used to obtain the instrument function of a VIPA-based spectrometer, and the other beam serves as excitation light and is incident on the combustion field through a first reflector and a second reflector in sequence, where it interacts with the combustion field gas to generate a scattering signal; a light receiving system collects and filters the scattered signal to obtain filtered Rayleigh-Brillouin scattering (FRBS), which is transmitted via optical fiber to a spectrometer and CCD 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 to a computer for subsequent data processing. The collected FRBS spectrum line is retrieved for temperature using 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 Tx and Tz signals. 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 receiving 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, which is used to filter out stray light in other bands. 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 present invention provides 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 light emitted by the laser interacts with the combustion field gas to generate a scattering signal. An xz-axis translation stage performs a two-dimensional scan of the combustion field. An iodine molecule absorption cell in a light-collecting system is used to filter out strong Mie scattering and background light. The obtained filtered Rayleigh-Brillouin scattering (FRBS) signal is spectrally resolved and signal collected by a VIPA-based spectrometer and a CCD, and then stored in a computer for data processing. The FRBS model is obtained by adding the transmittance function of the iodine molecule absorption cell to the Tenti S6 model. The collected FRBS spectral lines are fitted using the least squares method. The temperature is retrieved by seeking the best fitting value using temperature as the only variable.

[0010] The present invention's two-dimensional combustion field temperature measurement method utilizes an iodine molecular absorption cell to filter out strong Mie scattering and background light; employs the FRBS theoretical model to achieve absolute temperature measurement; and employs a two-dimensional scanning system to measure the two-dimensional profile of the combustion field. This method provides a method for retrieval of gas temperature based on FRBS in high-temperature environments with strong Mie scattering or background light, adapting to diverse environments and needs, offering greater flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Schematic diagram of the absorption spectrum of iodine molecules near 532 nm of the present invention;

[0012] Figure 2 It is a schematic diagram of the overall structure of the present invention;

[0013] Figure 3Schematic diagram of filtering Rayleigh-Brillouin scattering signals according to the present invention;

[0014] In the figure: 1-laser; 2-beam splitter, 3-reference optical path, 4-attenuator, 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

[0015] 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-linewidth single-longitudinal-mode continuous beam, which is split into two beams by a spectroscope 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, as excitation light, is incident on a combustion field 16 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 receiving system 17 collects and filters the scattering signal to obtain filtered Rayleigh-Brillouin scattering (FRBS), which is transmitted via an optical fiber to a spectrometer 7 and a CCD 8 for spectral resolution and signal acquisition. A scanning system completes a two-dimensional profile scan of the combustion field. The collected data is saved to a computer 9 for subsequent data processing. The collected FRBS spectrum line is used to retrieve the temperature using a FRBS theoretical model.

[0016] Among them, there are many ultrafine 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 in Figure 1 ). The absorption dip of the iodine molecule 1109 line is wider than the Mie scattering spectrum, but narrower than the Rayleigh scattering spectrum. The transmittance of the absorption dip is sufficiently low, while the transmittance on either side is relatively high, resulting in a high extinction ratio. The slope of the absorption dip is steep, resulting in good sensitivity, and the spacing between adjacent absorption lines is wide. In summary, the present invention selects the iodine molecule 1109 line as the absorption line to filter out Mie scattering and background light. The present two-dimensional combustion field temperature measurement method can filter out interference from Mie scattering and background light on the Rayleigh-Brillouin scattering (RBS) signal, enabling direct measurement of the combustion field temperature and two-dimensional profile scanning.

[0017] The VIPA-based spectrometer can achieve rapid spectrum measurement.

[0018] Furthermore, the scanning system includes 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 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.

[0019] 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 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 beam by the long focal length lens. The filtering system filters out Mie scattering, background light, and stray light in other bands. The spatially transmitted scattered light is coupled into the second fiber flange by the second focusing lens. 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 in other bands, and the iodine molecule absorption cell 22 is used to filter out Mie scattering and background light.

[0020] 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.

[0021] Furthermore, the FRBS theoretical model is based on the following formula:

[0022] 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: ;

[0023] Where, is the convolution operator; for 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.

[0024] Furthermore, the temperature of the collected FRBS spectrum is retrieved by using the FRBS theoretical model to obtain the temperature of the collected FRBS spectrum. , scattering angle , molecular mass , bulk viscosity , shear viscosity , thermal conductivity and internal specific heat capacity The known quantity is temperature As the only unknown variable, the FRBS spectrum is fitted with the 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. , bulk viscosity , shear viscosity , thermal conductivity and internal specific heat capacity Obtained by querying the relevant database based on the gas composition of the combustion field.

[0025] Furthermore, the combustion field can 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 state in the aviation field; and a high-temperature combustion field in the industrial field.

[0026] Specifically, the present invention provides a two-dimensional measurement method for the temperature of a combustion field. The tuned laser frequency is 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. The other beam serves as excitation light and passes through a first reflector 13 and a second reflector 15 in sequence to be incident on a combustion field 16, and interacts with the combustion field 16 to generate a scattering signal.

[0027] 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 in 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 in 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.

[0028] 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 beam by a long focal length lens 19. Stray light of other bands is filtered out by a 532nm±0.5nm narrowband filter 21. Background light and Mie scattering are filtered out by an iodine molecule absorption cell 22. The spatially transmitted scattered light 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 via an optical fiber for spectral resolution and signal acquisition. The collected data is saved in a computer 9 for subsequent data processing.

[0029] The present invention provides 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 light emitted by the laser interacts with the combustion field gas to generate a scattering signal. An xz-axis translation stage performs a two-dimensional scan of the combustion field. An iodine molecule absorption cell in a light-collecting system is used to filter out strong Mie scattering and background light. The obtained filtered Rayleigh-Brillouin scattering (FRBS) signal is spectrally resolved and signal collected by a VIPA-based spectrometer and a CCD, and then stored in a computer for data processing. The FRBS model is obtained by adding the transmittance function of the iodine molecule absorption cell to the Tenti S6 model. The collected FRBS spectral lines are fitted using the least squares method. The temperature is retrieved by seeking the best fitting value using temperature as the only variable.

[0030] The present invention's two-dimensional combustion field temperature measurement method utilizes an iodine molecular absorption cell to filter out strong Mie scattering and background light; employs the FRBS theoretical model to achieve absolute temperature measurement; and employs a two-dimensional scanning system to measure the two-dimensional profile of the combustion field. This method provides a method for retrieval of gas temperature based on FRBS in high-temperature environments with strong Mie scattering or background light, adapting to diverse environments and needs, offering greater flexibility.

[0031] 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, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent replacements for some of the technical features therein. Any modifications, equivalent replacements, 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 two-dimensional measurement method for combustion field temperature, characterized in that: The frequency of the tuned laser is stabilized at the center of the iodine molecule absorption line. The laser (1) outputs a narrow linewidth single longitudinal mode continuous light beam. The light beam is divided into two beams by a spectroscope (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. 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 is expressed as: f(T,ν)=[I0S0(ν;T,P,M,θ,η s ,...)T(ν)]*ω(ν) Where * is the convolution operator; I0 is S0(ν; T, P, M, θ, η s ,...) corresponding to the intensity; S0(ν; T, P, M, θ, η s ,...) is the RBS spectrum line normalized according to the Tenti S6 model and is related to the flow field state; ω(ν) is the instrument function of the VIPA-based spectrometer, and T(ν) is the iodine molecule transmittance function; The temperature of the collected FRBS spectrum is retrieved by using the FRBS theoretical model with pressure P, scattering angle θ, molecular mass M, and bulk viscosity coefficient η. b , shear viscosity coefficient η s , thermal conductivity k and internal specific heat capacity C are used as known variables, and temperature T is the only unknown variable. The FRBS spectrum is fitted by least squares. When the fitting residual is the smallest, the obtained temperature is considered to be the temperature corresponding to the detection spectrum. The scattering angle θ is determined by the circular wedge prism and can be adjusted according to the experimental conditions. The molecular mass M and bulk viscosity η are b , shear viscosity coefficient η s , thermal conductivity k and internal specific heat capacity C are obtained by querying the relevant database based on the gas composition of the combustion field.

2. The 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 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. By controlling the Tx and Tz signals, two-dimensional scanning measurement of the temperature of the combustion field (16) is realized.

3. The two-dimensional measurement method of combustion field temperature according to claim 1, characterized in that: The light receiving 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) includes a filter (21) and an iodine molecule absorption cell (22). The filter (21) is a narrowband filter and is used to filter out stray light in other bands. The iodine molecule absorption cell (22) is used to filter out Mie scattering and background light.

4. The 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) arranged in sequence.

Images