CN110400336B - Method for reconstructing flame three-dimensional temperature field of double-optical-field camera - Google Patents
Method for reconstructing flame three-dimensional temperature field of double-optical-field camera Download PDFInfo
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Abstract
The invention discloses a method for reconstructing a three-dimensional temperature field of flame by using a double-optical-field camera, which comprises the following steps: preprocessing the light field image to change a flame area in the light field image into a communication area; establishing a cylindrical medium model covering a flame communication area according to the preprocessed light field image; extracting a flame three-dimensional contour according to the established cylindrical medium model and the preprocessed light field image; and calculating the grids in the three-dimensional contour to finally obtain the three-dimensional temperature field. In the process of reconstructing the three-dimensional temperature field, the invention only needs to calculate the grid inside the flame, thereby greatly improving the reconstruction resolution of the three-dimensional temperature field and greatly reducing the calculation time and the calculation resources. The method provided by the invention has high automation degree, directly operates the shot light field image without a preset template, and can provide a technical basis for measuring the three-dimensional temperature field of the multimodal complex flame by using a radiation imaging method.
Description
Technical Field
The invention relates to a method for reconstructing three-dimensional temperature distribution of flame by using a double-optical-field camera, belonging to the technical field of flame temperature measurement.
Background
Flame combustion temperature is an important indicator that is closely related to the combustion process. The measurement of the flame three-dimensional temperature field is helpful for revealing the nature of the combustion phenomenon and the law of the combustion process, and has great significance for controlling the generation and the emission of combustion pollutants and the design and the optimized operation of a combustion system. The flame temperature field non-contact measurement technology based on radiation imaging utilizes the self radiation image of flame to obtain the temperature information of the flame, has the advantages of non-intruding type, high measurement precision, continuous real-time measurement, capability of measuring the three-dimensional temperature field of the flame and the like, and is researched and used by more and more researchers recently.
At present, flame radiation detection devices based on radiation imaging technology are mainly divided into two types, namely a common camera and a light field camera. The flame image collected by the common camera is the projection of the three-dimensional flame under a certain visual angle, and the direction of flame radiation cannot be distinguished, so that a plurality of cameras are needed to collect the multi-visual-angle radiation information of the flame, and the reconstruction of a complex flame three-dimensional temperature field is realized. Under the industrial environment, the fuel variety is various, the combustor structure is huge, the combustion process is complicated, the spatial position coupling between a plurality of cameras is difficult to be synchronous, the camera imaging quality is difficult to be consistent, and the application range of the combustor is greatly limited.
The light field camera is used as a flame radiation sampling device, and compared with the traditional camera in which a micro-lens array is additionally arranged between a detector and a main lens, the light field camera not only can record the intensity information of flame radiation with higher accuracy under a single exposure condition, but also can distinguish the direction of the flame radiation, can realize the reconstruction of a complex flame three-dimensional temperature field only by virtue of a double-light-field camera, and greatly reduces the installation cost and complexity of a measuring system.
However, an important factor restricting the development of the two-optical-field camera flame three-dimensional temperature field measurement technology at present is that the dividing method of the flame three-dimensional grid cannot be completely adapted to different flame three-dimensional profiles, which causes that areas without flame media also participate in flame radiation transmission calculation, increases the ill-conditioned nature of the flame three-dimensional temperature field reconstruction problem, causes longer reconstruction calculation time, and has low spatial resolution of the reconstructed flame three-dimensional temperature field, so that further intensive research is needed in the aspect of extracting the flame three-dimensional profiles.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a method for reconstructing a flame three-dimensional temperature field by using a dual-optical-field camera, which can reconstruct a flame three-dimensional temperature field at a faster speed and with a higher spatial resolution, in view of the above-mentioned shortcomings of the prior art.
In order to solve the technical problems, the invention adopts the technical scheme that:
a method for reconstructing a flame three-dimensional temperature field by using a dual-optical-field camera is characterized by comprising the following steps of:
preprocessing a light field image to change a flame area in the light field image into a communication area;
step two, establishing a cylindrical medium model covering a flame communication area according to the preprocessed light field imageDividing the medium model into cylindrical radial, circumferential and axial average parts
A grid of N R The number of the grids divided along the radial direction of the cylinder,
the number of the grids divided along the circumferential direction of the cylinder is Nz, and the number of the grids divided along the axial direction of the cylinder is Nz;
thirdly, extracting a flame three-dimensional contour according to the established cylindrical medium model and the preprocessed light field image;
and step four, establishing a radiation transmission equation according to the extracted flame three-dimensional profile and the radiation intensity value corresponding to each pixel of the light field image, and calculating the grids in the three-dimensional profile through an inversion algorithm to finally obtain the three-dimensional temperature field.
In the third step, the three-dimensional contour extraction comprises the following steps:
carrying out contour judgment on the cross section of the cylindrical medium corresponding to each row of pixels of the preprocessed light field image, and extracting a two-dimensional contour of a flame area;
and carrying out contour judgment on the cylindrical medium to finish flame three-dimensional contour extraction.
In the third step, the outline of the cross section of the cylindrical medium corresponding to each row of pixels in the preprocessed light field image is judged, and the criterion for extracting the two-dimensional outline of the flame area is as follows:
[Min(Q i ，N j )-Max(P i ，M j )]/(N j -M j )＞0.5 (1)
in the formula, P i Denotes the distance Q from the first intersection of the ith centerline and the circle to the center of the circle i Represents the distance from the second intersection point of the ith central line and the circle to the center of the circle, M j Represents the distance from the first intersection point of the central line and the jth radial grid to the center of the circle, N j Represents the distance from the second intersection of the centerline and the radially jth grid to the center of the circle, min (Q) i ，N j ) To representGet Q i ，N j Minimum of (1), max (P) i ，M j ) Indicates taking P i ，M j Maximum value of (1);
if the formula (1) is satisfied, the grid on the cross section is judged to be a flame area grid, and if not, the grid is an environment area grid.
In the third step, the outline judgment is carried out on the cylindrical medium, and the criterion for finishing the flame three-dimensional outline extraction is as follows:
in the formula,. DELTA.N z Representing the number of axial pixels contained in each three-dimensional volume grid;
if the formula (2) is met, the three-dimensional grid is judged to be a flame micro element body, otherwise, the three-dimensional grid is an environment micro element body;
and repeating the steps on the light field image acquired by the second camera to obtain the serial number of the corresponding flame micro element under the visual angle of the second camera. And (4) merging the flame micro-elements extracted under the two visual angles, determining the complete flame area grid serial number, and finishing the flame three-dimensional contour extraction.
The fourth step comprises:
1) The serial numbers of the flame micro-elements are reordered, whether the light corresponding to each pixel passes through the flame micro-elements of the cylindrical medium or not is judged, if so, the light is judged to be effective light, and if not, the light is judged to be ineffective light;
2) And establishing the following equation according to the spectral radiation intensity information of all the effective light rays:
wherein n represents the number of flame micro-elements each light ray passes through, M is the number of effective light rays, I λ (s) is the spectral radiation intensity of the flame in the s direction, I bλ Is the black body spectral radiation intensity of the flame infinitesimal body, kappa aλ Is a fireThe absorption coefficient of the flame micro-elements, i, j represents the ith, j flame micro-elements through which light passes along the transmission direction, r is the geometric length of the flame micro-elements through which the light passes, and lambda is the wavelength of the flame radiation light;
3) And (3) calculating the formula (3) by using an inversion algorithm to obtain the blackbody radiation intensity of each flame infinitesimal body, and calculating the temperature in each flame infinitesimal body grid by using the Planck's law, such as the formula (4), to obtain the final flame three-dimensional temperature field distribution.
In the formula, c 1 Is a first radiation constant, c 2 Is the second radiation constant of 3.7418 × 10 -16 W·m 2 And 1.4388 × 10 -2 m.K; t is the temperature of each flame element.
In the second step, the light field image preprocessing comprises the following steps:
demosaicing the light field image collected by the camera, and converting the demosaiced light field image into a true color image;
carrying out graying processing on the true color image, and converting the true color image into a grayscale image;
and setting a threshold, performing binarization processing on the gray level image, performing morphological closing operation, and filling gaps of the flame area to change the flame area into a connected area.
Compared with the prior art, the invention has the beneficial effects that:
the flame three-dimensional contour extraction method is combined with the imaging characteristics of the light field camera, flame three-dimensional contour extraction is directly carried out through the shot light field image, the operation is simple, and the automation degree is high. By extracting the three-dimensional profile, in the inversion process of the temperature field, the radiation transmission equation is established only by using the effective light rays penetrating through the flame micro-elements and the optical thickness of the grid in the three-dimensional profile penetrated by the effective light rays, so that the problem that the existing flame three-dimensional grid division method cannot be completely adapted to different flame three-dimensional profiles is solved, the reconstruction resolution of the three-dimensional temperature field is greatly improved, and the calculation time and the calculation resources are greatly reduced. The method can provide powerful basis for three-dimensional profile extraction and temperature reconstruction of multimodal complex flames.
Drawings
Fig. 1 is a grayscale image.
Fig. 2 is a binarized image.
Fig. 3 is an image after filling the flame area gap.
Fig. 4 is the established cylindrical medium model and coordinate system.
FIG. 5 is a cross-sectional view of a cylindrical medium.
Fig. 6 is a partially enlarged view.
Fig. 7 is a schematic diagram of three-dimensional contour extraction.
FIG. 8 is a schematic diagram of ray tracing.
Fig. 9 is a distribution diagram of the reconstructed three-dimensional temperature field at different cross-sections.
Detailed Description
The invention is further illustrated with reference to the following figures and specific examples. It is to be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalent modifications within the scope of the present invention as defined by the following claims.
A method for reconstructing a flame three-dimensional temperature field by using a dual-optical-field camera comprises the following steps:
firstly, demosaicing processing is performed on a light field image acquired by a camera, the demosaicing processing is converted into a true color image, then graying processing is performed, and the true color image is converted into a gray image, as shown in fig. 1. A threshold value is set, and the grayscale image is binarized as shown in fig. 2. The gaps of the flame region are filled, and the binary image is subjected to morphological closing operation, so that the flame region becomes a connected region as shown in fig. 3.
Step 2, three-dimensional contour extraction:
21 And establishing a cylindrical medium model and a coordinate system, and carrying out contour judgment on the cross section of the cylindrical medium corresponding to each row of pixels in the preprocessed image to realize two-dimensional contour extraction.
The established cylindrical medium model and the corresponding coordinate system are shown in fig. 4. The medium radius R is 16mm and the height L is 43.6mm. Equally dividing the cylindrical medium in radial direction, circumferential direction and axial direction
A grid.
And (3) carrying out flame edge detection on the graph 3, determining flame edge coordinates U (x, y) and V (x, y) corresponding to each row of pixels, establishing a flame cross section equation and a grid central line equation by taking [ U (x, y) + V (x, y) ]/2 as a circle center and | U (x, y) -V (x, y) |/2 as a radius, and obtaining a cross section image of the cylindrical medium in the graph 5.
And (3) carrying out two-dimensional contour extraction on the cross section of the cylindrical medium corresponding to each row of pixels of the image, if the cross section meets the formula (1), judging that the grid is a flame area grid on the cross section, otherwise, judging that the grid is an environment area grid, and taking a partial enlarged view of the flame cross section as shown in figure 6.
[Min(Q i ，N j )-Max(P i ，M j )]/(N j -M j )＞0.5 (1)
In the formula, P i ，Q i Respectively representing the distances of the ith central line from the first and second intersection points and the center of the circle, M j ，N j Respectively representing the distances, min (Q), between the centerline and the first and second intersection points and center of the radial jth grid i ，N j ) Represents taking Q i ，N j Minimum of (1), max (P) i ，M j ) Indicates taking P i ，M j Maximum value of (2).
And traversing 10 central line equations and 10 radial grids, and judging flame area grids and environment area grids in 10 multiplied by 10 grids corresponding to each cross section to realize two-dimensional contour extraction.
22 Carrying out contour judgment on the cylindrical medium to finish flame three-dimensional contour extraction.
221 And) the number of axial pixels included in each three-dimensional volume grid is 52 by calculation.
222 And adding the two-dimensional contour extraction results of all cross sections corresponding to 52 pixels in the axial direction included in the volume grid, if the two-dimensional contour extraction results satisfy the formula (2), determining that the volume grid is a flame infinitesimal body, otherwise, determining that the volume grid is an environment infinitesimal body, and recording the serial number of the corresponding flame infinitesimal body, wherein fig. 7 is a flame three-dimensional contour extraction schematic diagram.
In the formula,. DELTA.N z Representing the number of axial pixels contained in each voxel grid.
223 And) repeating the steps on the light field image collected by the second camera to obtain the serial number of the corresponding flame infinitesimal body under the view angle of the second camera.
224 And) merging the flame micro-elements extracted under the two visual angles, determining the complete flame area grid serial number, and finishing the flame three-dimensional contour extraction.
Step 4, three-dimensional temperature field reconstruction:
41 84 flame micro-elements and 1416 environment micro-elements are obtained according to the flame three-dimensional contour extracted in the step 3). The 84 flame micro-elements are reordered with the serial number 1,2. Screening the light rays, wherein the total number of the light rays is 286231, the number of the effective light rays passing through the flame micro-element is 90480, and the serial number of the effective light rays is recorded, as shown in fig. 8, the light ray 1,3 passes through the flame micro-element to be the effective light ray, and the light ray 2 does not pass through the flame micro-element to be the ineffective light ray.
2) And establishing the following equation according to the spectral radiation intensity information of all the effective light rays:
wherein n represents the number of flame micro-elements penetrated by each light ray, M is the serial number of the light ray, I λ (s) is the spectral radiant intensity of the flame in the s direction, in W/(m) 3 .sr)，I bλ Is the black body spectral radiation intensity of the flame infinitesimal body in unitsIs W/(m) 3 ·sr)，κ aλ Is the absorption coefficient of the flame infinitesimal body, with the unit k aλ ＝10m -1 I, j represents the i, j-th flame infinitesimal body through which the light passes in the transmission direction, r is the geometric length of the flame infinitesimal body through which the light passes, in m, λ is the wavelength of the flame radiation light, λ =610nm.
3) And (4) calculating the formula (3) by using an LSQR inversion algorithm to obtain the black body radiation intensity of each flame infinitesimal body, and calculating the temperature in each flame infinitesimal body grid by using the Planck's law, such as the formula (4). The temperature of the environment area is measured by a thermocouple to be 730K, and the distribution of the flame three-dimensional temperature field is finally obtained and is shown in figure 9.
In the formula, c 1 Is a first radiation constant, c 2 Is the second radiation constant of 3.7418 × 10 -16 W·m 2 And 1.4388 × 10 -2 m.K; t is the temperature of each flame element in K.
Claims (4)
1. A method for reconstructing a flame three-dimensional temperature field by using a dual-optical-field camera is characterized by comprising the following steps of:
preprocessing a light field image to change a flame area in the light field image into a communication area;
step two, establishing a cylindrical medium model covering a flame communication area according to the preprocessed light field image, and equally dividing the medium model into cylindrical medium models according to the radial direction, the circumferential direction and the axial direction of the cylinder
A grid of N R The number of the grids divided along the radial direction of the cylinder,
for the number of meshes divided circumferentially along the cylinder, nz being axially along the cylinderThe number of the divided grids;
thirdly, extracting a flame three-dimensional contour according to the established cylindrical medium model and the preprocessed light field image;
step four, establishing a radiation transmission equation according to the extracted flame three-dimensional profile and the radiation intensity value corresponding to each pixel of the light field image, and calculating the grids in the three-dimensional profile through an inversion algorithm to finally obtain a three-dimensional temperature field;
the fourth step comprises the following steps:
1) The serial numbers of the flame micro-elements are reordered, whether the light corresponding to each pixel passes through the flame micro-elements of the cylindrical medium or not is judged, if so, the light is judged to be effective light, and if not, the light is judged to be ineffective light;
2) And establishing the following equation according to the spectral radiation intensity information of all the effective light rays:
wherein n represents the number of flame micro-elements each light ray passes through, M is the number of effective light rays, I λ (s) is the spectral radiation intensity of the flame in the s direction, I bλ Is the black body spectral radiation intensity, κ, of the flame infinitesimal body aλ Is the absorption coefficient of the flame micro-element, i, j represents the i, j flame micro-element which the light passes through along the transmission direction, r is the geometric length of the flame micro-element which the light passes through, and lambda is the wavelength of the flame radiation light;
3) Calculating the formula (3) by using an inversion algorithm to obtain the blackbody radiation intensity of each flame infinitesimal body, and calculating the temperature in each flame infinitesimal body grid by using the Planck's law, such as the formula (4), to obtain the final flame three-dimensional temperature field distribution:
in the formula, c 1 Is the first radiationConstant, c 2 Is the second radiation constant of 3.7418 × 10 -16 W·m 2 And 1.4388 × 10 -2 m.K; t is the temperature of each flame element.
2. The method for reconstructing the three-dimensional temperature field of the flame by using the dual-optical-field camera according to claim 1, wherein in the third step, the three-dimensional contour extraction comprises the following steps:
carrying out contour judgment on the cross section of the cylindrical medium corresponding to each row of pixels in the preprocessed light field image, and extracting a two-dimensional contour of a flame area;
and carrying out contour judgment on the cylindrical medium to finish flame three-dimensional contour extraction.
3. The method for reconstructing the three-dimensional temperature field of the flame by using the dual-optical-field camera according to claim 2, wherein in the third step, the cross section of the cylindrical medium corresponding to each line of pixels of the preprocessed light field image is subjected to contour judgment, and the criterion for extracting the two-dimensional contour of the flame region is as follows:
[Min(Q i ,N j )-Max(P i ,M j )]/(N j -M j )＞0.5 (1)
in the formula, P i Denotes the distance Q from the first intersection of the ith centerline and the circle to the center of the circle i Represents the distance from the second intersection point of the ith central line and the circle to the center of the circle, M j Represents the distance from the first intersection point of the central line and the jth radial grid to the center of the circle, N j Represents the distance from the second intersection of the centerline and the radially jth grid to the center of the circle, min (Q) i ,N j ) Represents taking Q i ，N j Minimum of (1), max (P) i ,M j ) Indicates taking P i ，M j Maximum value of (1);
if the formula (1) is satisfied, the grid on the cross section is judged to be a flame area grid, and if not, the grid is an environment area grid.
4. The method for reconstructing the three-dimensional temperature field of flames by using the dual-light-field camera according to any one of claims 1 to 3, wherein in the second step, the light-field image preprocessing comprises the following steps:
demosaicing the light field image collected by the camera, and converting the demosaiced light field image into a true color image;
carrying out gray processing on the true color image, and converting the true color image into a gray image;
and setting a threshold, performing binarization processing on the gray level image, performing morphological closing operation, and filling gaps of the flame area to change the flame area into a connected area.
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