High-temperature combustion temperature field reconstruction system of laser spectroscopy

Abstract

The invention relates to a high-temperature combustion temperature field reconstruction system for laser spectroscopy. The system comprises the following steps: combining two beams of modulated laser into one beam by using an optical fiber beam combiner, and connecting the one beam into an optical switch; the optical switch is provided with an input channel and 64 output channels, each output channel is connected with one transmitting end assembly, the transmitting end assemblies transmit laser to a measurement area, the laser is received by the optical integrating sphere detection module and converted into electric signals, and then the electric signals are input into the signal analysis and processing module through the data acquisition system. The light intensity measurement module is used for processing background light intensity and transmission light intensity of a measurement area through digital phase locking and low-pass filtering; fitting an integral absorption area through a least square algorithm; and solving the high-temperature combustion temperature field by combining an adaptive gradient descent reconstruction algorithm with an ART iterative algorithm. According to the invention, the defects of weak anti-interference capability, low space utilization rate, insufficient effective path number and complex debugging of the existing measuring device are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of temperature field measurement, and in particular to a high-temperature combustion temperature field reconstruction system using laser spectroscopy. Background Art

[0002] The harsh working environment, complex structure, and limited measurement space of an aero-engine combustion chamber greatly limit the layout of optical sensors. On the one hand, only limited-angle measurement data can be collected, which poses a huge challenge to the high-precision distribution inversion of combustion parameters. On the other hand, most measurement methods can only achieve qualitative measurement of the combustion parameters of an aero-engine combustion chamber, and it is difficult to obtain quantitative information on the distribution of combustion parameters. For the few measurement methods that can obtain quantitative information, detectors with a large detection area are usually selected to improve the signal-to-noise ratio of measurement data, which further reduces the number of detectors that can be installed in a limited space, and it is difficult to reconstruct a combustion parameter distribution result with high spatial resolution.

[0003] Laser absorption spectroscopy technology has the advantages of simple measurement system, easy miniaturization, and strong anti-interference ability, and has played an important role in the measurement of temperature and velocity in combustion equipment such as high-temperature combustion furnaces, nuclear reactor chambers, and engine combustion chambers. Combining computational tomography technology, using the laser spectral signals collected at multiple angles, the distribution of the combustion chamber flame temperature and component concentration is inversely solved through an imaging algorithm.

[0004] For the existing laser absorption spectroscopy systems used to measure the combustion field state, on the one hand, traditional small-target infrared detectors are generally used, and the alignment requirement of the laser beam during measurement is high, and it is easily affected by the measurement environment, such as strong mechanical vibration, high heat radiation, and strong turbulence during intense combustion, and the anti-interference ability of the system is weak; on the other hand, in order to ensure as many effective optical paths as possible to obtain more information on the measurement area, most measurement systems build multiple sets of transmitting and receiving mechanical devices around the measurement area at the same time, with low space utilization rate and complicated and time-consuming pre-commissioning. And the traditional field reconstruction algorithm is sensitive to the initial value, has a long iteration time, and is easily trapped in a local optimal solution. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the present invention provides a high-temperature combustion temperature field reconstruction system using laser spectroscopy, which solves the disadvantages of the existing measurement device with weak anti-interference ability, low space utilization rate, insufficient number of effective paths, and complicated debugging.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A high-temperature combustion temperature field reconstruction system using laser spectroscopy includes a function generator, a laser controller, a distributed feedback laser, an optical fiber combiner, an optical switch, a transmitting end assembly, an optical integrating sphere detection module, a data acquisition system, and a signal analysis and processing module;

[0008] The fiber optic combiner combines two beams of laser light emitted by a distributed feedback laser, which have been modulated by the function generator and the laser controller, into one beam and connects it to the optical switch;

[0009] The optical switch has one input channel and 64 output channels. Each output channel is connected to one of the transmitting end components. The transmitting end components emit the laser light into the measurement area, which is received by the optical integrating sphere detection module and converted into an electrical signal, then transmitted to the data acquisition system, and finally input into the signal analysis and processing module;

[0010] The signal analysis and processing module is used to: process the background light intensity and transmitted light intensity in the measurement area through digital phase-locking and low-pass filtering; fit the integral absorption area through the least squares algorithm according to the Beer-Lambert law; solve the high-temperature combustion temperature field.

[0011] A further technical solution is:

[0012] The optical switch, according to a set program, sequentially outputs the laser light from the 1st output channel, the 2nd output channel, the 3rd output channel,..., the 64th output channel through an internal switch, and emits it from the corresponding transmitting end components, so that the optical path sweeps across the entire measurement area.

[0013] The time for the switch to switch different output channels is no more than 10 ms.

[0014] Each transmitting end component is arranged around the perimeter of the measurement area, and one optical integrating sphere detection module is set on each side. The four optical integrating sphere detection modules are distributed at the four corners of the measurement area.

[0015] The optical integrating sphere detection module includes an optical integrating sphere and a near-infrared detector;

[0016] The optical signal that reaches the target surface of the optical integrating sphere after passing through the measurement area is received by the infrared detector through the action of its internal cavity and converted into an electrical signal;

[0017] The electrical signal detected by the infrared detector is input into the data acquisition system through a signal line and stored in the signal analysis and processing module in the form of a digital signal;

[0018] The bandwidth of the near-infrared detector is 10 MHz.

[0019] The high-temperature combustion temperature field reconstruction system using the laser spectroscopy method further includes a fiber optic storage box, which stores the optical fibers extending from the transmitting end components in the box.

[0020] The fitting of the integral absorption area through the least squares algorithm includes:

[0021] Integrate the spectral absorptivity over the wavenumber domain as the integrated absorption area A, and the expression is as follows:

[0022]

[0023] In the above formula:

[0024] Among them, l is the optical path length passing through the gas medium, P(l) is the total gas pressure with the optical path length l passing through the gas medium, X(l) is the gas concentration with the optical path length l passing through the gas medium, and S v (T(l)) represents the line intensity at temperature T(l), and T(l) represents the gas temperature with the optical path length l passing through the gas medium, is expressed as the line shape function of the absorption spectrum and satisfies the normalization condition, v is the frequency,

[0025] S(T) represents the line intensity varying with temperature;

[0026] P represents the total gas pressure, X represents the gas concentration, and L represents the total optical path length.

[0027] The solution of the high-temperature combustion temperature field includes:

[0028] S1. Discretize the calculation region. When the distribution of the medium gas on the path is uneven, transform the expression of the integrated absorption area. The absorption of the medium gas in the discrete grid by the light ray, on the i-th laser path, the integrated absorption area A at frequency v v,i is:

[0029]

[0030] In the above formula, j is the discrete grid number, and x v,j represents the gas absorption coefficient in the j-th discrete grid; P represents the total gas pressure, and X j represents the gas concentration in the j-th discrete grid, and l ij represents the effective optical path length of the i-th laser beam passing through the j-th discrete grid.

[0031] Rewrite the above formula into the following matrix for tomography;

[0032] Lx v = A v

[0033] Among them, L represents the sensitivity matrix with dimensions M×N, M is the number of laser paths, N is the number of grids, and is calculated according to the geometric distribution of the laser before measurement; x v represents the reconstruction parameter matrix, and A vRepresent the integral absorption area matrix;

[0034] S2. Apply the adaptive gradient descent algorithm to perform the main iterative solution on the matrix constructed in S1 for high-temperature combustion temperature field image reconstruction, and use the ART algorithm to balance the data consistency constraint and non-negativity constraint in the reconstructed temperature field. The mathematical description of the ART algorithm is as follows:

[0035]

[0036] where, x (k+1,i) , x (k,i) are the iterative parameters of the i-th laser beam at the k+1-th and k-th steps; k represents the current iteration step; L i refers to the i-th row of the sensitivity matrix; A i is the i-th element of the absorbance; λ∈(0,2) is the relaxation factor used to control the convergence rate;

[0037] S3. Introduce the TV function smoothing constraint term as a prior regularization condition during the reconstruction process. For the two-dimensional reconstruction parameter x, the TV function smoothing constraint term is:

[0038]

[0039] where, TV(x) represents the function value of the TV function smoothing constraint term of the reconstruction parameter x, x(p,q) represents the reconstruction parameter in the p-th row and q-th column, x(p+1,q) represents the reconstruction parameter in the p+1-th row and q-th column, x(p,q+1) represents the reconstruction parameter in the p-th row and q+1-th column, and p and q respectively represent the row ordinal number and column ordinal number of the reconstruction parameter;

[0040] S4. Calculate the temperature of each discrete grid using the two-line temperature measurement method based on the two-dimensional reconstruction parameter x to obtain the reconstructed temperature field.

[0041] The calculation of the adaptive step size of the adaptive gradient descent algorithm includes:

[0042] Calculate the difference between the current reconstruction value and the previous reconstruction value according to the following formula:

[0043]

[0044] dA = |A (n) -A (n-1) |

[0045] where, dx ART is the difference between the n-th reconstruction value x (n) ART and the (n-1)-th reconstruction value x (n-1) ART in the main iteration of the ART algorithm; dxtv is the nth reconstructed value x of the TV function smoothing constraint term (n) tv and the (n - 1)th reconstructed value x (n-1) tv The difference; dA is the projected integral area A of the target image obtained in the nth main iteration (n) and the projected integral area A of the (n - 1)th iteration (n-1) The difference between them;

[0046] Update the gradient descent iteration step α of the TV function smoothing constraint term in the adaptive gradient descent algorithm according to the following formula tv :

[0047]

[0048] Among them, the parameter α ∈ (0, 1] is used to control the iteration step of the first main iteration;

[0049]

[0050] Among them, α red ∈ (0, 1], γ max ∈ (0, 1], and ε is a set threshold.

[0051] Two laser controllers and two distributed feedback lasers are arranged respectively. The function generator inputs the modulation signal into the corresponding distributed feedback laser controller through two output channels, and the laser controller modulates the output wavelength and light intensity of the corresponding distributed feedback laser.

[0052] The beneficial effects of the present invention are as follows:

[0053] The present invention realizes the switching of 64 measurement optical paths by a programmable optical switch device, and the minimum switching response time can reach 10 ms, thereby improving the spatial and temporal resolution of the reconstructed temperature field.

[0054] The present invention adopts an optical integrating sphere with a larger receiving target surface compared with an infrared detector, weakens the influence of the measurement environment, especially jitter, and is not affected by the incident angle, which is convenient for actual installation and debugging. At the same time, a controllable 64-channel optical switch can realize the fast and accurate positioning of the optical path, and more comprehensive optical path information can be obtained.

[0055] The requirements for laser collimation and alignment of the integrating sphere detection module of the present invention are greatly reduced. Even in an extremely harsh environment, the interference fringes in the received laser signal can be eliminated, thereby improving the stability of the laser signal. This module has a larger receiving target surface compared with the traditional infrared detector, and can equalize the light intensity when receiving signals, minimizing the influence of the measurement environment, especially vibration, on the optical path.

[0056] The miniaturized laser emission module of the present invention has the ability of multi-degree-of-freedom adjustment, thereby alleviating the attenuation of laser power. Only 4 sets of optical integrating sphere detection modules can capture the entire optical path. Working with such a small number of receivers, the equipment cost is significantly reduced, while the measured spatial resolution is significantly improved.

[0057] The present invention uses an adaptive gradient descent reconstruction algorithm combined with the ART iterative algorithm to achieve the consistency and non-negativity constraints of the reconstruction parameters, and at the same time adaptively controls the gradient descent iteration step size of the TV regularization term. Not only is the reconstruction accuracy improved, but also the reconstruction time is greatly improved, thereby improving the reconstruction time and spatial resolution of the entire system. It solves the problems of the traditional field reconstruction algorithm being sensitive to the initial value, having a long iteration time, and being prone to falling into local optimal solutions.

[0058] Other features and advantages of the present invention will be described in the subsequent specification, and part of them will be obvious from the specification or understood by implementing the present invention. Brief Description of the Drawings

[0059] Figure 1 It is a schematic connection structure diagram of the system according to the embodiment of the present invention.

[0060] Figure 2 It is a schematic flow diagram of the signal analysis and processing module of the embodiment of the present invention for solving the high-temperature combustion temperature field.

[0061] In the figure: 1, function generator; 2, laser controller; 3, distributed feedback laser; 4, fiber optic combiner; 5, optical switch; 6, fiber optic storage box; 7, transmitting end assembly; 8, optical integrating sphere detection module; 9, data acquisition system; 10, signal analysis and processing module. Detailed Embodiments

[0062] The following describes the detailed embodiments of the present invention with reference to the drawings.

[0063] See Figure 1 , the high-temperature combustion temperature field reconstruction system of the laser spectrometry of this embodiment includes a function generator 1, a laser controller 2, a distributed feedback laser 3, a fiber optic combiner 4, an optical switch 5, a transmitting end assembly 7, an optical integrating sphere detection module 8, a data acquisition system 9, and a signal analysis and processing module 10;

[0064] The fiber optic combiner 4 combines two beams of laser emitted by the distributed feedback laser 3 modulated by the function generator 1 and the laser controller 2 into one beam and connects it to the optical switch 5;

[0065] The optical switch 5 has one input channel and 64 output channels. Each output channel is connected to a transmitting end component 7. The transmitting end component 7 emits laser light into the measurement area, which is received by the optical integrating sphere detection module 8 and converted into an electrical signal, and then transmitted to the data acquisition system 9, and finally input into the signal analysis and processing module 10;

[0066] The signal analysis and processing module 10 is used to: process the background light intensity and transmitted light intensity in the measurement area through digital phase-locking and low-pass filtering; fit the integral absorption area through the least squares algorithm according to the Beer-Lambert law; solve the high-temperature combustion temperature field.

[0067] As a specific implementation manner, the optical switch 5 sequentially outputs the laser light from the 1st output channel, the 2nd output channel, the 3rd output channel,..., the 64th output channel through the internal switch according to the set program, and emits it from the corresponding transmitting end component 7, so that the optical path sweeps across the entire measurement area.

[0068] Among them, the time for the switch to switch different output channels is not greater than 10 ms.

[0069] Among them, the transmitting end component 7 collimates and converges the optical signal that has been transmitted over a long distance again, ensuring the power of the measurement signal in the measurement area.

[0070] As a specific implementation manner, each transmitting end component 7 is arranged around the perimeter of the measurement area, and preferably 15 to 18 transmitting end components 7 are arranged on each side; one optical integrating sphere detection module 8 is arranged on each side, and the four optical integrating sphere detection modules 8 are distributed at the four corners of the measurement area.

[0071] Among them, the optical integrating sphere detection module 8 includes an optical integrating sphere and a near-infrared detector;

[0072] The optical signal that reaches the target surface of the optical integrating sphere after passing through the measurement area is received by the infrared detector through the action of its internal cavity and converted into an electrical signal;

[0073] The electrical signal detected by the infrared detector is input into the data acquisition system 9 through the signal line and stored in the signal analysis and processing module 10 in the form of a digital signal.

[0074] As a specific implementation manner, the near-infrared detector is fixed to the outside of the cavity of the optical integrating sphere by a threaded connection method, and the bandwidth of the near-infrared detector is 10 MHz. The laser light in the cavity of the integrating sphere undergoes multiple diffuse reflections to achieve light intensity homogenization, and the received optical signal is received by the photodetector and converted into an electrical signal to obtain a light intensity signal.

[0075] As a specific implementation manner, two laser controllers 2 and two distributed feedback lasers 3 are arranged respectively. The function generator 1 inputs modulation signals into the corresponding distributed feedback laser controllers 3 through two output channels respectively, and the laser controller 2 modulates the output wavelength and light intensity of the corresponding distributed feedback laser 3. Specifically, the function generator 1 generates a modulation frequency f m1 signal, inputs the signal from channel one into the first laser controller 2, and the output wavelength and light intensity of the first distributed feedback laser 3 are tuned by the first laser controller 2; the function generator 1 inputs the modulation frequency f m2 signal from channel two into the second laser controller 2, and the output wavelength and light intensity of the second distributed feedback laser 3 are tuned by the second laser controller 2. The fiber optic combiner 4 couples the lasers modulated by the two distributed feedback lasers 3 into one beam and inputs it into the optical switch 5.

[0076] As a specific implementation manner, the high-temperature combustion temperature field reconstruction system of the laser spectrometry in this embodiment further includes a fiber optic storage box 6, which stores the optical fibers extended from the transmitting end assembly 7 into the box, so as to correspond the transmitting end assembly 7 with the output channels of the optical switch 5 one by one and arrange them neatly in sequence to facilitate the arrangement of the optical path.

[0077] The fitting of the integral absorption area by the least square algorithm in this embodiment includes:

[0078] Taking the integral of the spectral absorption rate in the wavenumber domain as the integral absorption area A, and the expression is as follows:

[0079]

[0080] In the above formula:

[0081] Among them, l is the optical path length passing through the gas medium, P(l) is the total gas pressure of the gas with the optical path length l passing through the gas medium, X(l) is the gas concentration of the gas with the optical path length l passing through the gas medium, and S v (T(l)) represents the line intensity at the temperature of T(l), and T(l) represents the gas temperature of the gas with the optical path length l passing through the gas medium, is expressed as the line shape function of the absorption spectrum and satisfies the normalization condition, v is the frequency,

[0082] S(T) represents the line intensity varying with temperature;

[0083] P represents the total gas pressure, X represents the gas concentration, and L represents the total optical path length.

[0084] Referring to Figure 2 , the solution of the high-temperature combustion temperature field in this embodiment includes:

[0085] S1. Based on the measurement principle of two-dimensional tomography reconstruction technology, in order to obtain the parameter information in the two-dimensional space within the measurement area, it is necessary to discretize the reconstruction area. First, the measurement area is divided into a 100×100 discrete grid. Assuming that parameters such as temperature within each discrete grid are evenly distributed, when the distribution of the medium gas on the path is uneven, the integral absorption area expression is transformed. After the light passes through the absorption of the medium gas within the discrete grid, on the i-th laser path, the integral absorption area A of frequency v v,i is:

[0086]

[0087] In the above formula, j is the discrete grid number, and x v,j represents the gas absorption coefficient within the j-th discrete grid; P represents the total gas pressure, and X j represents the gas concentration within the j-th discrete grid, and l ij represents the effective optical path length of the i-th laser beam passing through the j-th discrete grid.

[0088] The above formula is rewritten into the following matrix for tomographic imaging;

[0089] Lx v = A v

[0090] where L represents the sensitivity matrix of dimension M×N, M is the number of laser paths, and N is the number of grids, which is calculated according to the geometric distribution of the lasers before measurement; x v represents the reconstruction parameter matrix, and A v represents the integral absorption area matrix;

[0091] S2. The matrix constructed in S1 is solved by the adaptive gradient descent algorithm for the main iteration to reconstruct the high-temperature combustion temperature field image, and the ART algorithm (algebraic reconstruction method) is used to balance the data consistency constraint and non-negativity constraint in the reconstructed temperature field. The mathematical description of the ART algorithm is as follows:

[0092]

[0093] where x (k+1,i) and x (k,i) are the iterative parameters of the i-th laser beam at the k + 1-th and k-th steps; k represents the current iteration step; L i refers to the i-th row of the sensitivity matrix; A i is the i-th element of the absorbance; λ∈(0,2) is the relaxation factor used to control the convergence speed;

[0094] S3. During the reconstruction process, the TV function smoothing constraint term is introduced as a prior regularization condition. For the two-dimensional reconstruction parameter x, the TV function smoothing constraint term is:

[0095]

[0096] Among them, TV(x) represents the function value of the TV function smoothing constraint term of the reconstruction parameter x. x(p,q) represents the reconstruction parameter in the p-th row and q-th column. x(p + 1,q) represents the reconstruction parameter in the (p + 1)-th row and q-th column. x(p,q + 1) represents the reconstruction parameter in the p-th row and (q + 1)-th column. p and q respectively represent the row ordinal number and column ordinal number of the reconstruction parameter;

[0097] S4. Calculate the temperature of each discrete grid by using the two-line temperature measurement method based on the two-dimensional reconstruction parameter x (such as Figure 2 T in j ), and obtain the reconstructed temperature field.

[0098] Among them, the two-dimensional reconstruction parameter x is the local absorption coefficient. The calculation process of the two-line temperature measurement method is well-known in the art and will not be elaborated here.

[0099] Among them, the calculation of the adaptive step size of the adaptive gradient descent algorithm includes:

[0100] Calculate the difference between the current reconstruction value and the previous reconstruction value according to the following formula:

[0101]

[0102] dA = |A (n) -A (n-1) |

[0103] Among them, dx ART is the difference between the n-th reconstruction value x (n) ART and the (n - 1)-th reconstruction value x (n-1) ART in the main iteration of the ART algorithm; dx tv is the difference between the n-th reconstruction value x (n) tv of the TV function smoothing constraint term and the (n - 1)-th reconstruction value x (n-1) tv ; dA is the difference between the projected integral area A (n) of the target image obtained in the n-th main iteration and the projected integral area A (n-1) of the (n - 1)-th iteration;

[0104] Update the gradient descent iteration step size α tv of the TV function smoothing constraint term in the adaptive gradient descent algorithm according to the following formula:

[0105]

[0106] Among them, the parameter α ∈ (0, 1] is used to control the iteration step size of the first main iteration;

[0107]

[0108] Among them, α red ∈ (0, 1], γ max ∈ (0, 1], ε is a set threshold, preferably 10 -4 .

[0109] The adaptive gradient descent algorithm of this embodiment uses the ART iteration algorithm to achieve data consistency and non-negativity constraints, and at the same time adaptively controls the gradient descent iteration step size of the TV regularization term, which not only improves the accuracy but also reduces artifacts. It is widely applicable to industrial applications of image reconstruction.

[0110] Those of ordinary skill in the art can understand that the above description is only a preferred embodiment of the present invention and is not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-temperature combustion temperature field reconstruction system using laser spectroscopy, characterized in that: It comprises a function generator (1), a laser controller (2), a distributed feedback laser (3), a fiber beam combiner (4), an optical switch (5), a transmitter component (7), an optical integrating sphere detection module (8), a data acquisition system (9) and a signal analysis and processing module (10); The optical fiber combiner (4) combines two beams of laser light emitted by the distributed feedback laser (3) after being modulated by the function generator (1) and the laser controller (2) into one beam, and connects the beam to the optical switch (5); The optical switch (5) has one input channel and 64 output channels, each output channel is connected to one of the transmitting end components (7), the transmitting end component (7) emits laser light to the measurement area, which is received by the optical integrating sphere detection module (8) and converted into an electrical signal, which is then transmitted to the data acquisition system (9) and finally input into the signal analysis and processing module (10); The signal analysis and processing module (10) is used to: process the background light intensity and the transmitted light intensity of the measurement area through digital phase locking and low-pass filtering; fit the integrated absorption area through the least squares algorithm according to the Beer-Lambert law; and solve the high-temperature combustion temperature field.

2. The high temperature combustion temperature field reconstruction system of laser spectroscopy according to claim 1, characterized in that: The optical switch (5) outputs the laser light from the first output channel, the second output channel, the third output channel, ..., the 64th output channel in sequence through an internal switch according to a set program, and emits the laser light from the corresponding transmitting end component (7), so that the optical path sweeps across the entire measurement area.

3. The high temperature combustion temperature field reconstruction system of laser spectroscopy according to claim 2, characterized in that: The time for the switch to switch different output channels is no more than 10ms.

4. The high temperature combustion temperature field reconstruction system of laser spectroscopy according to claim 1, characterized in that: Each transmitting end assembly (7) is arranged around the periphery of the measuring area, and an optical integrating sphere detection module (8) is arranged on each side, and four optical integrating sphere detection modules (8) are distributed at the four corners of the measuring area.

5. The high temperature combustion temperature field reconstruction system of laser spectroscopy according to claim 1, characterized in that: The optical integrating sphere detection module (8) comprises an optical integrating sphere and a near-infrared detector; The light signal that passes through the measurement area and reaches the target surface of the optical integrating sphere is received by the infrared detector through the action of its internal cavity and converted into an electrical signal; The electrical signal detected by the infrared detector is input into the data acquisition system (9) through a signal line and is stored in the signal analysis and processing module (10) in the form of a digital signal; The bandwidth of the near infrared detector is 10 MHz.

6. The high temperature combustion temperature field reconstruction system of laser spectroscopy according to claim 1, characterized in that: It also includes an optical fiber storage box (6) which stores the optical fiber extending from the transmitting end assembly (7) in the box.

7. The high temperature combustion temperature field reconstruction system of laser spectroscopy according to claim 1, characterized in that: The method of fitting the integrated absorption area by the least squares algorithm comprises: The integral of the spectral absorbance in the wavenumber domain is taken as the integrated absorption area A, which is expressed as follows: In the above formula: Where l is the optical path length through the gas medium, P(l) is the total pressure of the gas through the gas medium with an optical path length of l, X(l) is the gas concentration through the gas medium with an optical path length of l, S v (T(l)) represents the line intensity at temperature T(l), T(l) represents the gas temperature with an optical path length l through the gas medium, It is expressed as a linear function of the absorption spectrum and satisfies the normalization condition, v is the frequency, S(T) represents the line intensity that varies with temperature; P represents the total gas pressure, X represents the gas concentration, and L represents the total optical path length.

8. The high temperature combustion temperature field reconstruction system of laser spectroscopy according to claim 7, characterized in that: The solution of the high temperature combustion temperature field comprises: S1. Discretize the calculation area. When the medium gas distribution on the path is uneven, transform the integral absorption area expression. The light is absorbed by the medium gas in the discrete grid. On the i-th laser path, the integral absorption area A with a frequency of v is v,i for: In the above formula, j is the discrete grid number, x v,j represents the gas absorption coefficient in the jth discrete grid; P represents the total gas pressure, X j represents the gas concentration of the jth discrete grid, l ij Represents the effective optical path length of the i-th laser beam passing through the j-th discrete grid. Rewrite the above formula into the following matrix for tomographic imaging; Lx v =A v Where L represents the sensitivity matrix with dimension M×N, M is the number of laser paths, and N is the number of grids, which is calculated according to the geometric distribution of the laser before measurement; x v represents the reconstruction parameter matrix, A v represents the integrated absorption area matrix; S2. The matrix constructed in S1 is solved by the adaptive gradient descent algorithm for the main iteration to reconstruct the high-temperature combustion temperature field image, and the ART algorithm is used to balance the data consistency constraints and non-negative constraints in the reconstructed temperature field. The mathematical description of the ART algorithm is as follows: Among them, x (k+1,i) 、x (k,i) is the iteration parameter of the i-th laser beam at the k+1th and kth steps; k represents the current iteration step length; L i A refers to the i-th row of the sensitivity matrix; i is the i-th element of absorbance; λ∈(0,2) is the relaxation factor used to control the convergence speed; S3. In the reconstruction process, the TV function smooth constraint term is introduced as a priori regularization condition. For the two-dimensional reconstruction parameter x, the TV function smooth constraint term is: Wherein, TV(x) represents the function value of the smooth constraint term of the TV function of the reconstruction parameter x, x(p,q) represents the reconstruction parameter of the p-th row and the q-th column, x(p+1,q) represents the reconstruction parameter of the p+1-th row and the q-th column, x(p,q+1) represents the reconstruction parameter of the p-th row and the q+1-th column, and p and q represent the row and column numbers of the reconstruction parameters respectively; S4. Calculate the temperature of each discrete grid using a two-line temperature measurement method based on the two-dimensional reconstruction parameter x to obtain a reconstructed temperature field.

9. The high temperature combustion temperature field reconstruction system of laser spectroscopy according to claim 8, characterized in that: The adaptive step size calculation of the adaptive gradient descent algorithm includes: The difference between the current reconstruction value and the previous reconstruction value is calculated as follows: dA=|A (n) -IN (n-1) | Among them, dx ART is the nth reconstruction value x of the ART algorithm in the main iteration (n) ART and the n-1th reconstruction value x (n-1) ART The difference between tv is the nth reconstruction value x of the smooth constraint term of the TV function (n) tv and the n-1th reconstruction value x (n-1) tv dA is the projected integral area A of the target image obtained in the nth main iteration (n) and the projected integral area A of the n-1th iteration (n-1) The difference between Update the gradient descent iteration step length α of the smooth constraint term of the TV function in the adaptive gradient descent algorithm according to the following formula: tv : Among them, the parameter α∈(0,1] is used to control the iteration step size of the first main iteration; Among them, α red ∈(0,1],γ max ∈(0,1], ε is the set threshold.

10. The high temperature combustion temperature field reconstruction system of laser spectroscopy according to claim 1, characterized in that: Two laser controllers (2) and two distributed feedback lasers (3) are arranged respectively, and the function generator (1) inputs modulation signals to the corresponding distributed feedback laser controllers (3) through two output channels respectively, and the laser controller (2) modulates the output wavelength and light intensity of the corresponding distributed feedback laser (3).

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