A hydroxyl three-dimensional number density quantification method based on ultraviolet band chemical self-luminescence

Abstract

The application provides a hydroxyl three-dimensional number density quantification method based on ultraviolet band chemical self-luminousness, which comprises establishing OH * an imaging model, building an ultraviolet imaging projection collection system, ultraviolet imaging system radiation calibration, projection imaging three-dimensional reconstruction and free radical number density distribution quantification. The method systematically establishes OH * from radiation emission, imaging through an ultraviolet optical system and response to a gray value on a detector, and combines an ultraviolet system radiation calibration method to obtain system parameters of the imaging system, and combines a three-dimensional reconstruction method to inversely obtain a three-dimensional number density distribution of the free radical. The method has the beneficial effect that the OH * radical number density three-dimensional quantification distribution measurement is realized on the ultraviolet band, and compared with a traditional square voxel modeling, a spherical voxel which is more in line with the spatial radiation characteristics of light energy is adopted, and the error of the existing model is corrected.

Description

Technical Field

[0001] This invention relates to the quantization of free radical number density, and more specifically to a method for quantifying the three-dimensional number density of hydroxyl groups based on ultraviolet-band chemiluminescence. Background Technology

[0002] Radical self-luminescence optical imaging (RBEM) for free radical number density quantification is an important research area in flame diagnostics. RBEM is a method that images free radicals generated during combustion. Compared to traditional methods or laser measurements, this imaging method does not interfere with the combustion field and requires no external light source, thus it is widely used in combustion diagnostics. The hydroxyl (OH) group, with a radiation wavelength around 309 nm... * Flame projection imaging is one of the main targets for free radical imaging, and its imaging results can be used in studies such as reaction location indication, pyrolysis rate distribution, and equivalence ratio calculation. However, since flame projection imaging itself is the result of integrating the three-dimensional flame along the line of sight from the imaging angle, the two-dimensional projection image obtained during the imaging process still needs to undergo further inversion to obtain OH. * On the one hand, the three-dimensional distribution information of OH in the ultraviolet band; on the other hand, the OH in the ultraviolet band. * Imaging often requires the participation of intensifier devices (such as ultraviolet image intensifiers), which poses a significant challenge to the quantification of free radicals. Therefore, current OH... * In imaging studies, most analyses remain at the relative value analysis stage, only able to reflect OH... * The relative spatial distribution information cannot be used to quantify its number density. Furthermore, the few existing exploratory works on quantitative analysis all target uniform axisymmetric flames and lack free radical radiation modeling methods. Summary of the Invention

[0003] In view of the above problems, this invention provides a method for quantifying the three-dimensional number density of hydroxyl groups based on chemiluminescence in the ultraviolet band. This method includes establishing OH... * The method includes imaging modeling, construction of an ultraviolet imaging projection acquisition system, radiometric calibration of the ultraviolet imaging system, 3D reconstruction of projection imaging, and quantification of free radical number density distribution. This method establishes an OH model with free radicals as the target system. * The system parameters of the imaging system are obtained by analyzing the complete process of radiation emission, imaging through the ultraviolet system, and the grayscale response on the detector, combined with the ultraviolet system radiation calibration method. The three-dimensional number density distribution of free radicals is then obtained by combining the three-dimensional reconstruction method.

[0004] This invention is specifically achieved through the following technical solution: a method for quantifying the three-dimensional number density of hydroxyl groups based on ultraviolet-band chemiluminescence, comprising the following steps:

[0005] (1) Establish OH* Imaging model

[0006] For the imaging region to be measured, based on the spatial radiation characteristics of free radicals, the imaging region is divided into uniform spherical voxels. Within each voxel, OH* is considered to be uniformly distributed. For a single spherical voxel, it can be regarded as a Lambertian radiator that radiates uniformly in space. After the radiation energy is transmitted in space, it is imaged by the optical system, received by the detector, and converted into grayscale output.

[0007] (2) Construct an ultraviolet imaging projection acquisition system

[0008] Combining the OH* imaging model and reconstruction method, an ultraviolet imaging system is built to acquire projections, including: optical path design, selection of imaging devices, imaging angle and distance;

[0009] (3) Radiation calibration of ultraviolet imaging system

[0010] The system includes an ultraviolet standard light source, an ultraviolet band response standard light source, an ultraviolet spectroradiometer, and a data acquisition computer. The standard light source is used to calibrate the ultraviolet imaging devices used in the ultraviolet imaging system and to confirm the overall response coefficient of the ultraviolet system to radiation.

[0011] (4) Reconstruction of the three-dimensional number density of free radicals

[0012] Based on the above process, firstly, flat-field correction is performed on the OH* projection image acquired by the ultraviolet imaging system, and then Zhang's calibration is used to perform imaging correction on the flat-field corrected image. At the same time, positional offset correction is performed for projections at different angles. Subsequently, the three-dimensional distribution of OH* is reconstructed using a three-dimensional reconstruction method to obtain the reconstructed three-dimensional distribution field F of OH*, which includes the spherical voxel distribution f of OH*. i 1≤i≤N, where N is the total number of voxels, and the OH* number density distribution within the voxels is obtained by combining the overall response coefficient obtained after correction.

[0013] Preferably, in step (1), the process of the spherical voxel outputting a grayscale response on the detector can be modeled as follows:

[0014]

[0015] Where G is the grayscale response of the detector, G0 is the dark response of the detector, K is the photoelectric conversion coefficient of the detector, η is the quantum conversion efficiency of the detector, and t e Let L be the imaging integration time, τ be the transmittance of the imaging system, and L be the image integration time. V For the radiance of a spherical OH* voxel, P v Let Ω be the radiant power of the spherical voxel, Ω be the imaging solid angle, and A be the radiant power of the voxel. VLet be the imaging area of ​​the spherical voxel on the detector pixel, h be Planck's constant, and v be the frequency;

[0016] Preferably, in step (1), the radiance of a single spherical voxel can be expressed as:

[0017]

[0018] Among them, L V spherical OH * The radiance of the voxel, h is Planck's constant, c is the speed of light, λ is the radiation wavelength, A is the Einstein coefficient, [N*] is the free radical density, V is the volume of the voxel region, S is the surface area of ​​the voxel, and λ1~λ2 is the radiation spectrum range.

[0019] Preferably, in step (2), an ultraviolet back-illuminated enhanced CMOS camera is selected as the imaging device, with 27 imaging angles evenly placed along a 180° semicircle, and an interval of 6.67° between adjacent imaging angles. A narrow-band filter with a center wavelength of 310nm is installed in front of the system, the distance between the imaging device and the flame target field is 30cm, and the imaging integration time is 20ms.

[0020] Preferably, in step (3), the calibration process is represented as follows:

[0021] G S =G0+K s L s

[0022] Among them, G S K represents the grayscale response of the imaging system to a standard ultraviolet light source. S L represents the overall response coefficient of the ultraviolet imaging device. S This represents the radiance of the ultraviolet standard light source.

[0023] Preferably, in step (4), OH * The number density distribution is expressed as:

[0024]

[0025] Among them, [OH*] i OH corresponding to the i-th voxel * Number density, S is the voxel surface area, and V is the voxel volume.

[0026] The advantages of this method are: 1) Compared to traditional methods that perform radiometric correction on two-dimensional free radical imaging using a single camera, this method employs a multi-angle projection three-dimensional reconstruction method, enabling the three-dimensional quantitative distribution measurement of the free radical number density of flames with complex variations, excluding symmetrical flames; 2) The method uses a spherical voxel approximation, which, compared to the traditional cubic voxel approximation, better reflects the true characteristics of spatial radiation of flame free radicals and corrects errors in existing models; 3) Existing calibration methods use broadband standard light sources, whose radiation characteristics deviate from ultraviolet free radical radiation. Furthermore, the camera's response in the broadband band also differs significantly from its response in the ultraviolet band. Therefore, this calibration method cannot reflect the actual response coefficient of the imaging system, leading to significant deviations in the correction process. This method uses a spherical voxel approximation, which is more consistent with the actual response coefficient of the imaging system. * A standard ultraviolet light source with the same radiation band can accurately reproduce the camera's response coefficient in the ultraviolet band. Attached Figure Description

[0027] Figure 1 The present invention OH * Structure diagram of number density quantization method.

[0028] Figure 2 The present invention OH * Schematic diagram of a spherical voxel imaging model.

[0029] Figure 3 This is a schematic diagram of the ultraviolet imaging projection acquisition system of the present invention.

[0030] Figure 4 This is a schematic diagram of the ultraviolet radiation calibration system of the present invention.

[0031] Figure 5 Flame projection imaging acquired by the ultraviolet imaging system in an embodiment of the present invention;

[0032] Figure 6 OH, an embodiment of the present invention * Number density distribution calculation results. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the embodiments.

[0034] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the field or according to the product instructions. Materials or equipment whose manufacturers are not specified are all conventional products that can be obtained by purchase.

[0035] This invention provides a method for quantifying the three-dimensional number density of hydroxyl groups based on chemiluminescence in the ultraviolet band, such as... Figure 1As shown, the method contains OH * The imaging model was established, and an ultraviolet imaging system was built based on the model to select imaging devices. Projected images were acquired from multiple imaging directions, and the overall response coefficient of the system was obtained using the ultraviolet radiation calibration method. Based on the three-dimensional reconstruction, the OH value of the target flame field was calculated. * Three-dimensional spatial number density distribution. This example focuses on imaging the combustion of a propane and isobutane mixed gas-air flame, requiring the acquisition of OH- ions during the combustion process. * Three-dimensional number density spatial distribution information. The specific implementation method is as follows:

[0036] Step (1) Build OH * Imaging model

[0037] For the imaging region to be measured, the imaging region is divided into uniform spherical voxels, and OH is considered to be within each voxel. * It is evenly distributed, such as Figure 2 As shown. Compared to the traditional square voxel region division method, the spherical voxel can be regarded as a uniform Lambertian radiator, which better reflects the actual radiation emission. For a single spherical voxel, its radiance can be expressed as:

[0038]

[0039] Among them, L V spherical OH * The radiance of the voxel, h is Planck's constant, c is the speed of light, λ is the radiation wavelength, A is the Einstein coefficient, [N*] is the free radical density, V is the volume of the voxel region, S is the surface area of ​​the voxel, and λ1~λ2 is the radiation spectrum range.

[0040] The process of a spherical voxel outputting a grayscale response on the detector requires conversion by the imaging system and the detector. This process can be modeled as follows:

[0041]

[0042] Where G is the grayscale response of the detector, G0 is the dark response of the detector, K is the photoelectric conversion coefficient of the detector, η is the quantum conversion efficiency of the detector, and t e For the imaging integration time, P v Let L be the radiant power of the spherical voxel, τ be the transmittance of the imaging system, and L be the radiant power of the voxel. V spherical OH * The radiance of the voxel, Ω is the imaging solid angle, and A is the image solid angle. V Let be the imaging area of ​​the spherical voxel on the detector pixel, h be Planck's constant, and v be the frequency.

[0043] Step (2): Selecting imaging devices and building an ultraviolet imaging system

[0044] Acquisition of multi-angle projection imaging is OH * A crucial foundation for number density reconstruction, combined with OH * Imaging models and reconstruction methods, and the construction of imaging systems require comprehensive consideration from multiple perspectives to meet OH requirements. * Number density reconstruction requirements. These include: optical path design, selection of imaging devices, imaging angle, and distance. When the free radical emission of the flame field under test is weak or the imaging frame rate is high, common ultraviolet detectors cannot respond to the target field, requiring an ultraviolet image intensifier to assist in imaging. The imaging angle affects OH. * When high accuracy is not required, OH can be reconstructed from 6-9 angles. * The distribution trend is considered, but when high accuracy is required, the number of reconstructed angles should be greater than or equal to nine. For example... Figure 3 This is just a schematic diagram of an ultraviolet imaging projection acquisition system.

[0045] Based on the imaging model in step (1), this embodiment selects an ultraviolet back-illuminated enhanced CMOS camera as the imaging device. To improve computational accuracy, 27 imaging angles are chosen, evenly placed along a 180° semicircle, with a 6.67° interval between adjacent imaging angles. A narrowband filter with a center wavelength of 310nm is installed in front of the system to filter stray light from other wavelengths. The distance between the imaging device and the flame target field is 30cm. The imaging integration time is 20ms.

[0046] Step (3) Radiation correction of ultraviolet imaging devices

[0047] Utilize Figure 4 The ultraviolet radiation calibration system shown performs radiation correction on ultraviolet imaging devices. During the calibration process, the imaging conditions are completely consistent with those during the projection acquisition described above. Therefore, the calibration result obtained is the overall response coefficient during the actual projection acquisition, which can be expressed as:

[0048]

[0049] Among them G S K represents the grayscale response of the imaging system to a standard ultraviolet light source. S L represents the overall response coefficient of the ultraviolet imaging device. S This represents the radiance of the ultraviolet standard light source.

[0050] Step (4), Flame Field OH * 3D number density reconstruction and quantization distribution calculation

[0051] like Figure 5As shown, the imaging results obtained from radiometric correction are used to perform planar field correction on the projected images at various angles to correct the detector's response inhomogeneity. Simultaneously, the system parameters obtained from Zhang's calibration are used to correct the corrected projection data, and the burner is used as a calibration object to further correct the imaging position offset of the corrected projection data at each angle. After preprocessing, a 3D reconstruction algorithm is used for reconstruction.

[0052] During the reconstruction process, the iteration control parameter was selected as 0.15, and the iteration precision was controlled as 10. -6 The maximum number of iterations is 200. The reconstructed voxel distribution F (containing OH) is obtained. * spherical voxel distribution f i (1≤i≤N, where N is the total number of voxels). For a single voxel, the above steps can be combined to obtain the OH* number density corresponding to that voxel:

[0053]

[0054] Among them, [OH * ] i Let S be the OH* number density corresponding to the i-th voxel, S be the voxel surface area, and V be the voxel volume. The calculation results for this example are as follows: Figure 6 As shown, this is the OH content on a cross-section 2.68 mm above the burner. * Number density distribution (unit (mol / m)) 3 )).

[0055] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for quantifying the three-dimensional number density of hydroxyl groups based on ultraviolet band chemical autofluorescence, characterized by, Comprising the following steps: (1) Establishing OH* imaging model For the imaging area to be measured, based on the spatial radiation characteristics of free radicals, the imaging area is divided into uniform spherical voxels, and OH* is considered to be uniformly distributed in each voxel. For a single spherical voxel, it can be regarded as a Lambertian radiator uniformly radiating in space. After the radiation energy is transmitted in space, it is imaged by the optical system and received by the detector, and then converted into gray-scale output; (2) Building an ultraviolet imaging projection collection system OH * The imaging model and reconstruction method are used for building an ultraviolet imaging system to collect projection, including light path design, selection of imaging device, imaging angle and distance. (3) Ultraviolet imaging system radiation calibration The system includes an ultraviolet standard light source, an ultraviolet waveband response standard light source, an ultraviolet spectral radiometer, and a collection computer. The standard light source is used to calibrate the ultraviolet imaging device used in the ultraviolet imaging system, and the overall response coefficient of the ultraviolet system to radiation is confirmed; (4) Free radical three-dimensional number density reconstruction Firstly, the OH * flat field correction is performed on the projection images, and the Zhang calibration is used to correct the images after flat field correction. Meanwhile, the position offset correction is performed on the projection images with different angles. Then, the OH * three-dimensional distribution is reconstructed by using the three-dimensional reconstruction method, and the reconstructed OH * three-dimensional distribution field F is obtained, which contains OH * spherical voxel distribution f i , 1≤i≤N, N is the total number of voxels, and the OH * number density distribution is obtained by combining the overall response coefficient obtained by correction; and OH * the number density distribution is represented as: , 1≤i≤N wherein [OH * ] i is the OH * number density, S is the surface area of the voxel, V is the volume of the voxel, K S is the overall response coefficient of the UV imaging device.

2. The method according to claim 1, wherein the method is a method for quantifying the three-dimensional number density of hydroxyl groups based on ultraviolet band chemical autofluorescence. In step (1), the process of the spherical voxel outputting the gray-scale response on the detector is modeled as: ； where G is the gray response of the detector, G0 is the dark response of the detector, K is the photoelectric conversion coefficient of the detector, η is the quantum conversion efficiency of the detector, t is the imaging time, P is the power of the imaging system, and A is the imaging area of the spherical OH e volume on the detector. v where P is the radiated power of the spherical OH V volume, τ is the transmittance of the imaging system, L is the distance between the imaging system and the spherical OH * volume, Ω is the imaging solid angle, A is the imaging area of the spherical OH V volume on the detector, and h is the Planck constant. where f is the frequency.

3. The method according to claim 2, wherein the method is characterized by, In step (1), the single spherical voxel radiance is represented as: ； where L V is the spherical OH * radiance of the voxel, h is the Planck constant, c is the speed of light, λ is the radiation wavelength, A is the Einstein coefficient, [N*] is the radical number density, V is the voxel region volume, S is the voxel surface area, and λ1 ~ λ2 is the radiation spectral range.

4. The method according to claim 1, wherein the method is characterized by, In step (2), an ultraviolet back-illuminated enhanced CMOS camera is selected as the imaging device, the imaging angle is selected as 27, and it is placed uniformly along a 180° semicircle with an interval of 6.67° between adjacent imaging angles. The system is equipped with a narrow-band filter with a center wavelength of 310 nm in front, the imaging device is 30 cm away from the flame target field, and the imaging integration time is 20 ms.

5. The method according to claim 1, wherein the method is characterized by, In step (3), the calibration process is represented as: ； where G S is the gray scale response of the imaging system to the UV standard light source, L S is the radiance of the UV standard light source.

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