Combustion field temperature measurement method and device based on Raman vibration conversion spectrum

Abstract

The invention discloses a combustion field temperature measurement method and device based on a Raman vibration conversion spectrum, and the method comprises the steps: extracting an equipment instrument function through a cold flow nitrogen spectrum, and carrying out the convolution of a nitrogen theoretical spectrum data set through the instrument function, thereby obtaining a synthetic spectrum; synthesizing a monotonic function curve of the spectral band intensity ratio along with the temperature change through nonlinear fitting; raman scattering light generated by the measurement area is obtained; converting the generated Raman scattering light into a spectral signal; processing the spectral signal, and extracting a nitrogen Raman Stokes signal spectral band intensity ratio after asymmetric Voigt function fitting; and substituting the band intensity ratio into the monotonic function curve, and carrying out back calculation to obtain a temperature measurement result. According to the method, related characteristic information of the Raman vibration-rotation spectrum and the temperature is utilized, and the asymmetric Voigt function is combined to carry out fine fitting on the Raman spectrum, so that the limitation of the existing temperature measurement technology is overcome, and more accurate and quicker combustion field temperature measurement is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of energy detection, and particularly relates to a combustion field temperature measurement method and device based on Raman vibration spectrum. BACKGROUND

[0002] Combustion research is an important branch of the energy field, and is of great significance for improving combustion efficiency, energy saving and emission reduction, and controlling pollution emissions. Temperature, as an important parameter in the combustion process, directly affects the combustion efficiency and the composition of the emissions. Therefore, accurate, fast and stable temperature measurement of the combustion field is particularly important for understanding and optimizing the combustion process. With the rapid development of laser technology, photoelectric detection technology and data image processing technology, the temperature diagnosis of the combustion field has also developed rapidly.

[0003] The existing temperature measurement methods can be mainly divided into two categories: contact temperature measurement and non-contact temperature measurement. For contact temperature measurement, there are thermocouple method, electrothermal method, electrical conductivity method, etc. These methods directly invade the combustion object / environment to measure the temperature, which will damage the flow field and affect the temperature of the measured area. Non-contact temperature measurement based on spectral analysis, such as Rayleigh scattering method, uses laser to irradiate the measured object and measures the Rayleigh scattering light to obtain one-dimensional temperature information. However, this technology has low spatial and temporal resolution, and it is difficult to determine the edge of the light, and the test uncertainty is relatively high; laser-induced fluorescence (LIF) selects specific components and energy levels, and then measures the temperature of the detected components through absorption / radiation process. However, this method requires the selection of fluorescent dye dissolved in the measured fluid, and the use of specific wavelength laser to excite the measured flow field. Finally, the camera collects the fluorescence signal. However, this technology requires the addition of tracer particles, which may affect the combustion process. At the same time, the LIF technology has low spatial and temporal resolution, and requires complex calibration and data processing; laser-induced phosphor method (LIP) selects appropriate phosphor substances and deposits them on the surface of the measured substance or in the flow field. An appropriate wavelength laser is used to irradiate the phosphor substance, and a camera is used to collect the phosphor signal. However, this technology requires a reference image of the layer surface at a consistent temperature, and LIP technology is suitable for liquid fuel combustion and has limited application in other types of combustion scenarios; spontaneous Raman scattering (SRS) measures the process mainly by using a laser to irradiate the measured substance, using a stretcher to achieve pulse stretching, using a filter to filter Rayleigh signals, and finally using a camera to collect Raman scattering light signals.

[0004] In the Raman vibration-rotation spectrum of a molecule, the Raman vibration Q branch is a special region of the Raman spectrum related to the vibration-rotation energy level transition of the molecule. The Q branch does not accompany the change of the rotation energy level, and it provides the information of the internal vibration state of the molecule, usually in the form of relatively sharp peaks, and the position and intensity of the peaks can be used to analyze the structure of the molecule and the influence of the environment on it. Therefore, the Raman vibration Q branch contains a lot of useful information, and by obtaining the useful information, the temperature of the measured substance can be obtained. Generally, the Q branch is mainly related to pure vibration transition, i.e. ΔJ=0. In the Raman vibration-rotation spectrum of nitrogen, the ratio of the first upper state band (J=1) spectral band intensity (including the tail wing part of the ground state band) Δλ1 to the Q branch ground state band spectral band intensity (J=0) Δλ0 shows an ideal functional relationship, and according to this point, temperature measurement can be realized. SUMMARY

[0005] To solve the above technical problems, the present application provides a combustion field temperature measurement method and device based on Raman vibration-rotation spectrum, which uses the correlation characteristic information of Raman vibration-rotation spectrum and temperature, and combines the fine fitting of Raman spectrum by asymmetric Voigt function, to overcome the limitations of existing temperature measurement technology, and realize more accurate and faster combustion field temperature measurement.

[0006] In one aspect, the present application provides a combustion field temperature measurement method based on Raman vibration-rotation spectrum, comprising:

[0007] An instrument function is extracted from a cold flow nitrogen spectrum extraction device, and a synthetic spectrum is obtained by convolving the instrument function with a nitrogen theoretical spectrum data set;

[0008] A nonlinear fitting is performed on a monotonous function curve of the change of the spectral band intensity ratio with temperature;

[0009] Raman scattered light is obtained from a measurement region;

[0010] The generated Raman scattered light is converted into a spectrum signal;

[0011] The spectrum signal is processed to extract the spectral band intensity ratio of the nitrogen Raman Stokes signal spectrum after fitting by the asymmetric Voigt function, the spectral band intensity ratio is substituted into the monotonous function curve, and the temperature measurement result is obtained by inverse calculation.

[0012] In another aspect, the present application provides a combustion field temperature measurement device based on Raman vibration-rotation spectrum, comprising: a spectrum synthesis module, a synthetic spectrum fitting module, a Raman scattered light acquisition module, a Raman scattered light conversion module, a data processing module and a temperature measurement result obtaining module;

[0013] The spectrum synthesis module is used to extract an instrument function from a cold flow nitrogen spectrum extraction device, and obtain a synthetic spectrum by convolving the instrument function with a nitrogen theoretical spectrum data set;

[0014] The synthetic spectrum fitting module is used for nonlinearly fitting a monotonic function curve of synthetic spectrum band intensity ratio changing with temperature;

[0015] The Raman scattered light acquisition module is used to acquire the Raman scattered light generated in the measurement area;

[0016] The Raman scattered light conversion module is used to convert the generated Raman scattered light into a spectral signal;

[0017] The data processing module is used to process the spectral signal and extract the nitrogen Raman-Stokes signal band intensity ratio after asymmetric Voigt function fitting;

[0018] The module for obtaining temperature measurement results is used to substitute the spectral band intensity ratio into the monotonic function curve and obtain the temperature measurement result by reverse calculation.

[0019] Technical Effects of the Invention: Disclosed are a combustion field temperature measurement method and device based on Raman vibrational-rotational spectroscopy. By fitting spectral data using an asymmetric Voigt function, more accurate spectral information is obtained, thereby improving the accuracy of temperature measurement. By using a monotonic function curve showing the band intensity ratio as a function of temperature obtained in the synthetic spectrum, the temperature can be calculated from the fitted curve simply by measuring the experimental Raman spectrum and extracting the band intensity ratio, eliminating the need for complex data comparison, thus reducing costs and increasing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0021] Figure 1 This is a flow chart of a combustion field temperature measurement method based on Raman vibrational-rotational spectroscopy according to an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram of the structure of a combustion field temperature measurement device based on Raman vibrational-rotational spectroscopy according to an embodiment of the present invention; wherein 1 is a laser, 2 is an adjustable attenuator, 3 is a focusing system, 4 is a region to be measured, 5 is a light trap, 6 is a 45° total reflection mirror, 7 is a filter, 8 is a convex lens, 9 is a grating spectrometer, and 10 is a computer;

[0023] Figure 3 This is a schematic diagram of the function extraction results of the instrument according to an embodiment of the present invention;

[0024] Figure 4 This is a schematic diagram of the theoretical spectrum of nitrogen gas according to an embodiment of the present invention;

[0025] Figure 5 This is a schematic diagram of the synthetic spectrum of nitrogen gas according to an embodiment of the present invention;

[0026] Figure 6 This is a schematic diagram of the synthetic nitrogen band intensity ratio-temperature curve according to an embodiment of the present invention;

[0027] Figure 7 Schematic diagram of the spectrum fitting results of the experiment in the embodiment of the present invention. DETAILED DESCRIPTION

[0028] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0029] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0030] like Figure 1 As shown, this embodiment provides a combustion field temperature measurement method based on Raman vibrational-rotational spectroscopy, including: fitting the nitrogen spectrum under cold flow conditions using an asymmetric Voigt function to obtain an instrument function for an SRS test device. The instrument function is convolved with theoretical nitrogen spectral data to obtain a series of nitrogen synthetic spectra at known temperatures; a 0.28 nm width at the peak positions of the synthetic spectrum ground state band and the first upper state band is selected as the integral wavelength range for calculating the spectral band intensities; the vibrational Q-branch band ground state band intensities Δλ1 and the first upper state band intensities Δλ2 of the nitrogen synthetic spectra at different temperatures are integrated. Here, a 0.28 nm width at the peak positions of the synthetic spectrum ground state band and the first upper state band is selected as the integral wavelength range for calculating the spectral band intensities; the ratio R of Δλ2 to Δλ1 is calculated; and finally, a nonlinear fitting of the band intensity ratio R-temperature curve is used to construct a monotonic function of the band intensity ratio with respect to temperature. This completes the preparation of the reference data set for temperature measurement.

[0031] The laser generates laser light, which passes through the adjustable attenuation plate and the focusing system in sequence and converges at a certain point in the measurement area. The scattered light generated in the measurement area enters the low-pass filter through a 45° total reflection mirror to obtain a Stokes signal. The light is then converged by a convex lens and enters the grating spectrometer to be converted into a spectral signal, thus completing the Raman signal collection work of the combustion field.

[0032] The computer processes the collected spectral signals. Since the collected spectral signals contain multiple components, the spectral signals are first screened to obtain the spectral signals of nitrogen. The spectral signals of nitrogen are subjected to noise filtering and baseline correction to improve the quality of spectral data. The spectral signals of nitrogen are subjected to peak normalization and fitting. Here, the asymmetric Voigt function is used, and the spectral is fitted by using the nonlinear least squares method. Here, the Levenberg-Marquart algorithm is used. The mathematical formula of the asymmetric Voigt function is as follows:

[0033]

[0034] The center wavelength corresponding to the single peak on the spectrum is taken as the demarcation line, and there is one fitting function on the left and right of the center wavelength. The units of the parameters of the formula are nm, and the specific meanings are as follows: Δλ lg is the left Lorentz broadening; Δλ ld is the right Lorentz broadening; Δλ vg is the left voigt broadening; Δλ vd is the right voigt broadening; λ0 is the center wavelength; and λ is the wavelength.

[0035] The voigt broadening in the formula can be calculated by formula (2), wherein Δλ D is the Doppler broadening.

[0036]

[0037] The test-measured nitrogen spectrum is fitted by using the asymmetric Voigt function, and the physical information of the ground state band and the first upper state band is extracted, including the ground state band intensity, the first upper state band intensity, and the ratio of the first upper state band intensity to the ground state band intensity. Here, the region with a width of 0.28 nm at the peak position is selected to calculate the intensity by integration. The calculated band intensity ratio is brought into the band intensity ratio-temperature curve of the synthesized nitrogen spectrum, and the temperature value T is inversely calculated by linear interpolation.

[0038] A methane / air premixed McKenna standard flat burner is used, and one of the 22 working conditions published by DLR is selected for SRS temperature measurement technology verification.

[0039] Figure 3 The extraction results of the instrument function of the test equipment by using the Voigt function and the asymmetric Voigt function are shown, and the fitting residuals are 0.0469% and 0.0406%, respectively, indicating that the asymmetric Voigt function can more accurately describe the spectral line shape. Figure 4 is part of the theoretical nitrogen spectrum calculated by the RAMEs software, Figure 5 is a series of synthesized spectra obtained by convolving the theoretical nitrogen spectrum with the instrument function. The band intensity ratio-temperature curve is extracted from the synthesized spectrum, and the result is shown inFigure 6 . Figure 7 For the fitting results of the test nitrogen spectrum, the band intensity ratio of the test spectrum is extracted and substituted into the synthetic nitrogen band intensity ratio-temperature curve to obtain the temperature result, and the final calculation result is shown in Table 1.

[0040] Table 1

[0041] Actual temperature / K Measured temperature / K Relative error / % 1980 1991.3 0.57

[0042] As Figure 2 shown, the embodiment also provides a combustion field temperature measurement device based on Raman shift spectrum, comprising: a spectrum synthesis module, a synthetic spectrum fitting module, a Raman scattered light acquisition module, a Raman scattered light conversion module, a data processing module and an obtained temperature measurement result module.

[0043] The spectrum synthesis module is used to extract the instrument function of the cold flow nitrogen spectrum extraction device, and the instrument function is convolved with the nitrogen theoretical spectrum data set to obtain a synthetic spectrum.

[0044] The synthetic spectrum fitting module is used to nonlinearly fit a monotonic function curve of the band intensity ratio of the synthetic spectrum with temperature.

[0045] The Raman scattered light acquisition module is used to acquire Raman scattered light generated in the measurement region.

[0046] The Raman scattered light conversion module is used to convert the generated Raman scattered light into a spectrum signal.

[0047] The data processing module is used to process the spectrum signal and extract the band intensity ratio of the nitrogen Raman Stokes signal spectrum after asymmetric Voigt function fitting.

[0048] The obtained temperature measurement result module is used to substitute the band intensity ratio into the monotonic function curve to inversely calculate and obtain the temperature measurement result.

[0049] Further, the Raman scattered light acquisition module is composed of a laser 1, an adjustable attenuation sheet 2, a focusing system 3 and a light trap 5.

[0050] The selected laser 1 is an Nd:YAG laser, and the laser 1 emits 532nm wavelength laser. The laser outlet successively passes through the adjustable attenuation sheet 2, the focusing system 3 and the light trap 5.

[0051] The adjustable attenuation sheet 2 is used to adjust the intensity of the outgoing laser to prevent high-intensity laser from breaking through the substance and affecting the measurement result.

[0052] The focusing system 3 is composed of a plano-concave lens and a plano-convex lens. By adjusting the distance between the two optical devices, the incoming laser can be focused at different positions of the measurement region 4, facilitating measurement.

[0053] Light trap 5 is used to absorb useless light, prevent laser from causing harm to experimental equipment and personnel.

[0054] Further, the Raman scattering light conversion module is composed of a 45° total reflection mirror 6, a filter 7, a convex lens 8 and a grating spectrometer 9.

[0055] The 45° total reflection mirror 6 reflects the Raman scattering light generated in the measurement area, changes the light path so that the signal collection is more convenient, and the system is more compact as a whole.

[0056] The filter 7 can filter out the strong Rayleigh signal in the scattering signal, improve the signal-to-noise ratio of the Raman signal as a whole, thereby improve the imaging quality of the Raman spectrum, and the strong Rayleigh signal can also be suppressed to prevent the spectrometer signal from being oversaturated and damaged. Here, a low-pass filter is used, only the Stokes signal is retained.

[0057] The convex lens 8 further converges the light out of the filter 7, so that the spectrometer can collect all the Raman signals, and the signal strength is ensured.

[0058] The grating spectrometer 9 converts light into spectral signals, and the spectral signals are transmitted to the computer 10 through the data line for further data processing.

[0059] Further, the data processing module is completed on the computer 10, and the computer 10 is responsible for processing the spectral signals converted by the grating spectrometer 9, including data screening, noise filtering, baseline correction, spectral fitting and spectral information extraction functions.

[0060] The present application adopts asymmetric Voigt function to fit spectral data, and obtains more accurate spectral fitting results.

[0061] The present application aims at the characteristic information of Raman vibration spectrum, and measures the temperature by the fitting curve of the spectral band intensity ratio of nitrogen and temperature. The band intensity ratio of the experiment is inversely calculated by interpolation in the fitting curve. Here, nitrogen is used as the temperature marker, and other markers can be used instead for the combustion environment without nitrogen.

[0062] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any changes or replacements easily thought by those skilled in the art within the technical range disclosed by the present application should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A combustion field temperature measurement method based on Raman vibrational rotational spectroscopy, characterized in that: include: The cold-flow nitrogen spectrum is used to extract the instrument function of the equipment, and the instrument function is convolved with the nitrogen theoretical spectrum data set to obtain a synthetic spectrum; Nonlinear fitting is used to synthesize the monotonic function curve of the spectrum band intensity ratio changing with temperature; Acquiring Raman scattered light generated in the measurement area; Converting the generated Raman scattered light into a spectral signal; Processing the spectral signal to extract the nitrogen Raman Stokes signal band intensity ratio after asymmetric Voigt function fitting; The spectral band intensity ratio is substituted into the monotonic function curve and the temperature measurement result is obtained by inverse calculation.

2. The combustion field temperature measurement method based on Raman vibrational rotation spectroscopy according to claim 1, characterized in that: Converting the generated Raman scattered light into a spectral signal includes: Laser light is generated by a laser, which passes through an adjustable attenuation plate and a focusing system in sequence and converges at a certain point in the measurement area. The scattered light generated in the measurement area enters a low-pass filter through a 45° total reflection mirror to obtain a Stokes signal. The Stokes signal is then converged by a convex lens into a grating spectrometer and converted into a spectral signal.

3. The combustion field temperature measurement method based on Raman vibrational rotation spectroscopy according to claim 1, characterized in that: Processing the spectral signal to obtain a temperature measurement result includes: The spectral signal is screened to obtain a spectral signal of nitrogen; the spectral signal of nitrogen is preprocessed, and the preprocessed nitrogen spectral signal is fitted using an asymmetric Voigt function, and the fitting method uses a nonlinear least squares Levernberg-Marquart algorithm to extract the Raman band signal intensity ratio of the first upper state band and the ground state band in the fitted spectral signal; the band intensity ratio is substituted into a monotonic function curve of the synthetic spectrum band intensity ratio varying with temperature to obtain a temperature measurement result.

4. The combustion field temperature measurement method based on Raman vibrational rotational spectroscopy according to claim 3, characterized in that: The asymmetric Voigt function I(λ) is calculated as follows: Where Δλ lg is the left Lorentz broadening; Δλ ld is the right Lorentz broadening; Δλ vg is the left voigt broadening; Δλ vd is the right voigt broadening; λ0 is the center wavelength; λ is the wavelength.

5. A device for measuring combustion field temperature based on Raman vibrational rotational spectroscopy according to any one of claims 1 to 4, characterized in that: include: Spectrum synthesis module, synthetic spectrum fitting module, Raman scattered light acquisition module, Raman scattered light conversion module, data processing module and temperature measurement result acquisition module; The spectrum synthesis module is used to use the cold flow nitrogen spectrum extraction equipment instrument function, and the instrument function is convolved with the nitrogen theoretical spectrum data set to obtain a synthetic spectrum; The synthetic spectrum fitting module is used for nonlinearly fitting a monotonic function curve of synthetic spectrum band intensity ratio changing with temperature; The Raman scattered light acquisition module is used to acquire the Raman scattered light generated in the measurement area; The Raman scattered light conversion module is used to convert the generated Raman scattered light into a spectral signal; The data processing module is used to process the spectral signal and extract the nitrogen Raman-Stokes signal band intensity ratio after asymmetric Voigt function fitting; The module for obtaining temperature measurement results is used to substitute the spectral band intensity ratio into the monotonic function curve and obtain the temperature measurement result by reverse calculation.

6. The combustion field temperature measurement device based on Raman vibrational rotational spectroscopy according to claim 5, characterized in that: The module for obtaining Raman scattered light is composed of a laser (1), an adjustable attenuation plate (2), a focusing system (3), an area to be measured (4), and a light trap (5); The laser (1) is used to emit laser light of a preset size and wavelength, and the laser light passes through the adjustable attenuation plate (2), the focusing system (3), and the light trap (5) in sequence after exiting the laser light; The adjustable attenuation plate (2) is used to adjust the intensity of the emitted laser; The focusing system (3) is composed of a plano-concave lens and a plano-convex lens, and the distance between the plano-concave lens and the plano-convex lens is adjusted to focus the incoming laser light on different positions of the area to be measured (4); The light trap (5) is used to absorb useless light.

7. The combustion field temperature measurement device based on Raman vibrational rotational spectroscopy according to claim 5, characterized in that: The Raman scattered light conversion module is composed of a 45° total reflection mirror (6), a filter (7), a convex lens (8), and a grating spectrometer (9); The 45° total reflection mirror (6) is used to reflect the Raman scattered light generated in the measurement area; The filter (7) is used to filter out the stronger Rayleigh signal in the scattered signal; The convex lens (8) is used to converge the light emitted from the filter (7) to obtain converged light; The grating spectrometer (9) is used to convert the converged light into a spectral signal and send the spectral signal to the data processing module.

8. The combustion field temperature measurement device based on Raman vibrational rotational spectroscopy according to claim 5, characterized in that: The data processing module comprises a computer (10), and the computer (10) is used to process the spectrum signal converted by the spectrometer.

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