High-temperature and high-pressure temperature field measurement method based on low-resolution ultraviolet absorption tomography

Abstract

The present invention discloses a high-temperature and high-pressure temperature field measurement method based on low-resolution ultraviolet absorption tomography. The method comprises: selecting the electronic transition of NO or OH in the ultraviolet band as the absorption spectrum measurement object according to the temperature of the temperature field to be measured, and selecting the vibration spectrum band of the measurement object according to the concentration and size conditions of the temperature field to be measured to determine the wavelength range to be measured; selecting a broadband light source and a low-resolution spectrometer as the light source and detector required for the absorption spectrum measurement, respectively; establishing an optical path network for absorption tomography, wherein each optical path uses the selected broadband light source and low-resolution spectrometer, and the absorption spectrum of the measurement object is measured on all optical paths. The temperature of each spatial position is calculated from the absorption spectrum signals collected by each optical path, and the temperature field is reconstructed. The present invention can realize accurate temperature measurement by absorption spectrum under high-temperature and high-pressure conditions, and realize accurate measurement of high-temperature and high-pressure temperature fields by combining with a tomography reconstruction algorithm.

Description

Technical Field

[0001] The present invention belongs to the fields of spectrum measurement and temperature measurement, and in particular relates to a high-temperature and high-pressure temperature field measurement method based on low-resolution ultraviolet absorption tomography. Background Art

[0002] Temperature is an important physical parameter related to combustion power. In the fields of energy industry, aerospace, etc., it is closely related to performance, efficiency, economy, safety, etc. Therefore, there is an urgent need for accurate temperature measurement. With the continuous advancement of related industrial technologies, the demand for temperature measurement is also expanding towards higher temperatures, higher pressures, faster response speeds, and overall temperature field measurement. For example, the development and optimization of engines for automobiles, ships, aerospace, etc., urgently need to accurately measure the high temperature (~2000K) and high pressure (>1MPa) temperature field of the combustion chamber, so as to accurately evaluate the efficiency, performance, heat resistance, safety, etc. of the engine and combustion chamber, and serve as a data reference for further optimization.

[0003] Because traditional contact measurement techniques cannot meet these temperature measurement requirements, optical temperature measurement technologies have been widely researched and rapidly developed. Common temperature field measurement techniques include absorption spectroscopy, PLIF (Planar Laser Induced Fluorescence), and CARS (Coherent Anti-Stokes Raman Scattering). PLIF has poor temperature measurement accuracy and suffers from increased collisional quenching with increasing pressure, significantly reducing signal strength. CARS offers high temperature measurement accuracy, but can only measure a single point at a time, resulting in slow temperature field measurement and high optical path precision requirements, making it difficult to apply to complex, dynamic temperature fields. In contrast, absorption spectroscopy offers advantages such as calibration-free measurement, high temperature measurement accuracy, high temporal resolution, and low optical requirements. Furthermore, its mature, low-cost, compact size, and ease of integration make it an indispensable and common technique for in-situ temperature field measurements.

[0004] However, currently used high-wavelength-resolution absorption spectroscopy techniques struggle to measure temperature fields at high temperatures and high pressures. Currently, no research using absorption spectroscopy has successfully measured high-pressure temperature fields, not only in real-world temperature fields, but also under ideal laboratory conditions. The main issue is that commonly used laser absorption spectroscopy or absorption spectroscopy using high-resolution spectrometers, such as mid-step spectroscopy, are both high-wavelength-resolution spectroscopy techniques with resolution superior to or comparable to line broadening. The temperature measurement principle is to extract the integral area characteristics of individual spectral lines to determine temperature information. However, under high-pressure conditions, line broadening is severe and overlap interference is severe, making it impossible to identify individual spectral lines and effectively measure temperature. Some studies have attempted to extract effective information from heavily overlapping spectra under uniform conditions at high temperatures and high pressures using wavelength modulation or supercontinuum spectroscopy, but these efforts have been limited in accuracy and effectiveness, and absorption spectroscopy has not yet been applied to non-uniform temperature fields. Therefore, in the fields of temperature measurement and combustion power, there is an urgent need to develop a high-temperature and high-pressure temperature field measurement method based on absorption spectroscopy, and low-resolution ultraviolet absorption spectroscopy is one feasible approach. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-temperature and high-pressure temperature field measurement method based on low-resolution ultraviolet absorption tomography to address the problem that the current existing absorption spectroscopy temperature measurement technology mainly adopts high-wavelength resolution spectral measurement, and the spectral lines overlap severely under high-pressure conditions, making it impossible to realize the measurement of non-uniform temperature fields under high-temperature and high-pressure conditions. The method can avoid the influence of spectral line broadening under high-pressure conditions and realize high-temperature and high-pressure temperature field measurement.

[0006] One aspect of the present invention provides a high-temperature and high-pressure temperature field measurement method based on low-resolution ultraviolet absorption tomography, comprising:

[0007] Step S1: Select the electronic transition of NO or OH in the ultraviolet band as the absorption spectrum measurement object according to the temperature of the temperature field to be measured, and select the vibration spectrum band of the measurement object according to the concentration and size conditions of the temperature field to be measured to determine the wavelength range to be measured;

[0008] Step S2: Selecting a broadband light source and a low-resolution spectrometer as the light source and detector required for absorption spectrum measurement, respectively;

[0009] Step S3: Build an optical path network for absorption tomography. Each optical path uses the broadband light source and low-resolution spectrometer selected in step S2. The absorption spectrum of the measurement object selected in step S1 is measured on all optical paths. The temperature of each spatial position is calculated from the absorption spectrum signals collected by each optical path to complete the temperature field reconstruction.

[0010] Preferably, in a temperature field above 1200° C., the OH spectrum is selected as the measurement object, and according to the size of the temperature field and the OH concentration conditions, five spectral bands with different absorption intensities in the range of 220 nm to 330 nm are selected;

[0011] In the temperature field below 1200°C, the NO spectrum is selected as the measurement object, and two spectral bands within the range of 216nm to 240nm are selected.

[0012] Preferably, when the OH spectrum is selected as the measurement object, five vibration bands of Δv=0, 1, 2, 3, and 4 are selected; when the NO spectrum is selected as the measurement object, two vibration bands of Δv=0 and -1 are selected.

[0013] Preferably, when the OH spectrum is selected as the measurement object, an LED is selected as the broad-spectrum light source; when the NO spectrum is selected as the measurement object, a deuterium lamp, a xenon lamp or a laser-driven white light source is selected as the broad-spectrum light source.

[0014] Preferably, the low-resolution spectrometer includes a grating spectrometer and a Fourier transform spectrometer.

[0015] Preferably, when the OH spectrum is selected as the measurement object, a grating spectrometer with a resolution of 0.1 nm is selected; when the NO spectrum is selected as the measurement object, a grating spectrometer with a resolution of 0.5 nm is selected.

[0016] According to the high-temperature and high-pressure temperature field measurement method based on low-resolution ultraviolet absorption tomography of the above aspects of the present invention, by adopting OH or NO electron transitions in the ultraviolet band as the absorption spectrum measurement object, and adopting a wide-spectrum light source and a low-resolution spectrometer as the measurement light source and detector, it is possible to achieve accurate temperature measurement of the absorption spectrum under high-temperature and high-pressure conditions, and combine the tomography reconstruction algorithm to achieve accurate measurement of the high-temperature and high-pressure temperature field. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the present invention, the following briefly introduces the drawings used in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive efforts.

[0018] Figure 1 This is a flow chart of a high-temperature and high-pressure temperature field measurement method according to one embodiment of the present invention;

[0019] Figure 2 This is a comparison chart of the low-resolution ultraviolet absorption spectrum of NO and OH in one embodiment of the present invention and the commonly used high-resolution absorption spectrum of H2O under high-pressure conditions;

[0020] Figure 3 This is a comparison chart of the ultraviolet absorption intensity of OH and NO and the infrared absorption intensity of H2O at 2000K according to one embodiment of the present invention;

[0021] Figure 4 This is a comparison chart of the UV absorption spectra of NO at different temperatures according to an embodiment of the present invention;

[0022] Figure 5 1 is a schematic diagram of simulation steps according to an embodiment of the present invention;

[0023] Figure 6 Schematic diagram of simulation results of an embodiment of the present invention. DETAILED DESCRIPTION

[0024] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0025] The embodiment of the present invention provides a high temperature and high pressure temperature field measurement method based on low resolution ultraviolet absorption chromatography, such as Figure 1 As shown, the high-temperature and high-pressure temperature field measurement method according to the embodiment of the present invention includes steps S1 to S3.

[0026] In step S1, according to the temperature of the temperature field to be measured, the electronic transition of NO or OH in the ultraviolet band is selected as the absorption spectrum measurement object, and according to the concentration and size conditions of the temperature field to be measured, the vibration spectrum band of the measurement object is selected to determine the wavelength range to be measured.

[0027] The main functions of selecting NO or OH UV absorption spectrum as the measurement object are detailed as follows:

[0028] (1) The NO or OH spectrum in the UV band has the ability to be immune to high pressure influence at low resolution. Figure 2 As shown in the figure, the commonly used high-resolution absorption spectrum of H2O is compared with the low-resolution spectrum of NO or OH in the ultraviolet band: the OH spectrum resolution is 0.1nm, and the NO spectrum resolution is 0.5nm, which is far worse than the spectral line self-broadening of about 1pm. Figure 2 As shown in the figure, it can be seen that compared with the current high-resolution absorption spectrum of H2O, which has serious spectral overlap or even becomes a piece under high-pressure conditions and cannot effectively distinguish independent spectral lines to complete temperature measurement, the low-resolution spectrum of UV NO or OH has basically the same structure under high-pressure conditions as under normal pressure, and is basically not negatively affected by high-pressure conditions.

[0029] (2) NO or OH has stronger absorption in the ultraviolet band. Figure 3 As shown, the OH line intensity can reach up to 10 at 2000K. -17 cm / mole or more, much higher than the H2O infrared absorption spectrum commonly used for temperature measurement 10 -22 cm / mole (near infrared) ~ 10 -20 Line intensity in cm / mole (mid-infrared).

[0030] In one embodiment of the present invention, in step S1, when determining the wavelength range to be measured, appropriate molecules to be measured and vibrational bands to be measured are selected according to actual conditions such as temperature, concentration, and size of the temperature field to be measured to determine the wavelength range to be measured:

[0031] (1) In a temperature field above 1200°C, the OH spectrum can be selected as the measurement object, which has strong absorption and high temperature measurement sensitivity. Moreover, according to the actual temperature field size and OH concentration conditions, the appropriate spectrum band can be selected from the five vibration spectrum bands of Δv = 0, 1, 2, 3, and 4 with different absorption intensities in the range of 220nm to 330nm, such as Figure 3 As shown, the line intensities of the five vibrational bands cover 10 -20 cm / mole~10 -17 Multiple orders of magnitude of cm / mole allow selection of spectral bands with moderate absorption intensity to avoid saturation due to excessive absorption or signal-to-noise ratio being affected by weak absorption.

[0032] (2) In a temperature field below 1200°C, the NO spectrum can be selected as the measurement object, and the Δv=0,-1 band in the range of 216nm to 240nm is used for temperature measurement. The simulated NO low-resolution (0.5nm) spectra at different temperatures are as follows: Figure 4 As shown, the temperature measurement sensitivity can be improved by utilizing the sensitivity of the spectral band intensity ratio to temperature based on the different changes in the overall intensity of the two spectral bands with temperature.

[0033] In step S2, a broadband light source and a low-resolution spectrometer are selected as the light source and detector for the absorption spectrum measurement, respectively, and the spectrometer resolution required for temperature measurement is determined. A low-resolution spectrometer refers to a spectrometer with a resolution several orders of magnitude lower (0.1 nm to 1 nm) than the line broadening (~1 pm), including but not limited to grating spectrometers and Fourier transform spectrometers.

[0034] Broad-spectrum light sources may include, but are not limited to, LEDs, deuterium lamps, xenon lamps, laser-driven white light sources, and the like. Spectrometers may include grating spectrometers, Fourier transform spectrometers, and the like.

[0035] In one embodiment of the present invention, a broadband light source and a spectrometer may be selected as follows:

[0036] (1) Broad spectrum light source: For OH spectrum temperature measurement, LED is selected, which has low cost, high power, small size, good stability and safety. For NO spectrum temperature measurement, since LED cannot provide the corresponding wavelength output, flash xenon lamp is selected as the light source, which has low cost and high power. Deuterium lamp or laser-driven white light source with better stability but higher cost can also be selected.

[0037] (2) Spectrometer: For OH spectrum temperature measurement, a grating spectrometer with a resolution of 0.1 nm is selected. For NO spectrum temperature measurement, a grating spectrometer with a resolution of 0.5 nm is selected. Due to the lower resolution, it can be achieved by a portable spectrometer, reducing the size and cost of the equipment.

[0038] In step S3, a commonly used absorption chromatography method is used to combine the ultraviolet absorption spectrum measurement method described in steps S1 and S2 with the tomographic reconstruction method to perform high-temperature and high-pressure non-uniform temperature field measurement, specifically including steps S31 to S33:

[0039] Step S31: Establishing an optical path network for absorption chromatography, where each optical path uses the broadband light source and spectrometer selected in step S2;

[0040] Step S32: measuring the absorption spectrum of the measurement object selected in step S1 on all optical paths;

[0041] Step S33: using a tomographic measurement method, the temperature field is calculated from the absorption spectrum signals collected by each optical path.

[0042] In an embodiment of the present invention based on simulation, the schematic diagram of step S3 is as follows: Figure 5 As shown, the temperature field reconstruction results are as follows Figure 6 The simulated temperature field is a trimodal distribution consisting of three superimposed Gaussian distributions, with a maximum temperature of 2500K and a pressure of 3 MPa. The optical network established in step S31 consists of four parallel optical paths spaced 45° apart, with 12 equally spaced parallel paths in each direction. The OH ultraviolet absorption spectrum with a Δv=0 vibration band from 305nm to 321nm is used, and the spectrometer resolution is 0.1nm.

[0043] In step S33, different absorption spectrum tomography measurement methods can be selected, including various currently disclosed tomography algorithms. The following tomography measurement method is preferably used:

[0044] (1) Experimental absorption spectrum α obtained by measuring each optical path exp As well as the absorbance theoretical model α(T, X), the temperature T and concentration X, and the corresponding α(T, X) are obtained by least squares fitting:

[0045] (T, X) = arg min || α exp +ln{-exp[-α(T,X)]*Φ}|| 2

[0046] Where Φ is the spectrometer instrument function, which is a Gaussian function with resolution as the full width at half maximum, and α(T, X) is the absorbance theoretical model:

[0047] α(T, X)=PXLS p (T)·φ v

[0048] Where P is the pressure, L is the optical path, φ v is the spectral line shape function, S p (T) is the unit pressure line strength.

[0049] (2) For the absorbance α(T, X) obtained for each light path, the absorption coefficient κ(T, X) at each spatial position can be calculated by applying a tomography algorithm. This process is a common method in the field of absorption spectral tomography.

[0050] (3) For the absorption coefficient κ(T, X) at each spatial position, the temperature T and concentration X at each spatial position are obtained by least squares fitting:

[0051] (T,X)=arg min||κ(T,X)-PXS p (T)·φ v || 2

[0052] The temperature T at each spatial position constitutes the temperature field, thus completing the tomographic measurement of the temperature field.

[0053] In this simulation-based embodiment, the reconstruction results of the high-temperature and high-pressure temperature field at 3 MPa and 2500 K are as follows: Figure 6 As shown, the reconstructed temperature field is basically consistent with the original temperature field, with an average temperature deviation of 3.4%, which preliminarily verifies the effectiveness of the present invention.

[0054] The high-temperature and high-pressure temperature field measurement method based on low-resolution ultraviolet absorption tomography in the above-mentioned embodiment of the present invention adopts OH or NO electron transitions in the ultraviolet band as the absorption spectrum measurement object, and adopts a wide-spectrum light source and a low-resolution spectrometer as the measurement light source and detector, so as to achieve accurate temperature measurement of the absorption spectrum under high-temperature and high-pressure conditions, and finally completes the accurate measurement of the high-temperature and high-pressure temperature field by combining the tomography reconstruction algorithm.

[0055] The present invention utilizes the advantage of low-resolution spectra in the ultraviolet band being immune to the influence of high pressure, as well as the ability of wide-spectrum light sources and spectrometers to simultaneously measure a large number of spectral lines, to realize absorption spectral tomography measurement of high-temperature and high-pressure temperature fields. It effectively solves the difficult problems of current high-resolution absorption spectra such as laser absorption and medium-step spectrometers, which have serious spectral line overlap, low broadening model accuracy, and difficulty in realizing high-temperature and high-pressure temperature field measurement under high-pressure conditions. It provides effective spectral measurement technology support for the non-contact measurement needs of high-temperature and high-pressure temperature fields in the fields of combustion diagnosis, energy and power, aerospace, etc.

[0056] The above description is merely illustrative of certain exemplary embodiments of the present invention. It goes without saying that those skilled in the art will be able to modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims.

Claims

1. A high-temperature and high-pressure temperature field measurement method based on low-resolution ultraviolet absorption tomography, characterized in that: include: Step S1: Select the electronic transition of NO or OH in the ultraviolet band as the absorption spectrum measurement object according to the temperature of the temperature field to be measured, and select the vibration spectrum band of the measurement object according to the concentration and size conditions of the temperature field to be measured to determine the wavelength range to be measured; Step S2: Selecting a broadband light source and a low-resolution spectrometer as the light source and detector required for absorption spectrum measurement, respectively; Step S3: Build an optical path network for absorption tomography. Each optical path uses the broadband light source and low-resolution spectrometer selected in step S2. The absorption spectrum of the measurement object selected in step S1 is measured on all optical paths. The temperature of each spatial position is calculated from the absorption spectrum signals collected by each optical path to complete the temperature field reconstruction.

2. The method according to claim 1, characterized in that In a temperature field above 1200°C, the OH spectrum is selected as the measurement object, and according to the size of the temperature field and the OH concentration conditions, five spectral bands with different absorption intensities in the range of 220nm to 330nm are selected; In the temperature field below 1200°C, the NO spectrum is selected as the measurement object, and two spectral bands within the range of 216nm to 240nm are selected.

3. The method according to claim 2, characterized in that When the OH spectrum is selected as the measurement object, five vibration bands of Δv=0, 1, 2, 3, and 4 are selected; when the NO spectrum is selected as the measurement object, two vibration bands of Δv=0 and -1 are selected.

4. The method according to any one of claims 1 to 3, characterized in that When the OH spectrum is selected as the measurement object, an LED is selected as the broad-spectrum light source; when the NO spectrum is selected as the measurement object, a deuterium lamp, a xenon lamp, or a laser-driven white light source is selected as the broad-spectrum light source.

5. The method according to any one of claims 1 to 3, characterized in that Low-resolution spectrometers include grating spectrometers and Fourier transform spectrometers.

6. The method according to claim 5, characterized in that When the OH spectrum is selected as the measurement object, a grating spectrometer with a resolution of 0.1 nm is selected; when the NO spectrum is selected as the measurement object, a grating spectrometer with a resolution of 0.5 nm is selected.

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