CN112611477B - Device for reconstructing combustion flame temperature field through laser absorption spectrum scanning light path - Google Patents

Abstract

The invention relates to a device for reconstructing a combustion flame temperature field by a laser absorption spectrum scanning optical path, comprising a function generator, a laser controller, a distributed feedback laser, an optical fiber beam splitter, a reflector, a laser transmitting and receiving device, a hollow retroreflector and Signal processing components, mirrors, laser transmitting and receiving devices correspond to the number of beams modulated by the fiber beam splitter; the fiber beam splitter divides the laser modulated by the distributed feedback laser into multiple beams, and each beam is transmitted and received by the corresponding laser The device emits to the corresponding mirror, which is rotated by a high-speed stepping motor, distributed in the space to ensure that the optical path sweeps the entire area to be measured, returns in parallel through the hollow retroreflector, and is received and converted into an electrical signal by the laser transmitting and receiving device. , to get the light intensity signal. The invention realizes the integration of signal sending and receiving, reduces measurement components, miniaturizes and integrates, realizes rapid reconstruction of temperature field, obtains more comprehensive optical path information, and improves measurement accuracy.

Description

A Device for Reconstructing the Temperature Field of a Combustion Flame by Laser Absorption Spectrum Scanning Optical Path

technical field

The invention relates to the technical field of temperature field measurement devices, in particular to a device for reconstructing the temperature field of a combustion flame by scanning an optical path with a laser absorption spectrum.

Background technique

Aeroengine is a kind of complex and precise thermal machinery, which directly affects the performance, reliability and economy of aircraft. The combustion chamber is an essential and important part of the engine. It releases the chemical energy in the fuel through combustion, converts the chemical energy into heat energy, generates high-temperature and high-pressure gas, and improves the engine's working ability. When designing the combustion chamber, it is necessary to ensure good combustion stability, high combustion efficiency and low emission pollution.

Based on TDLAS technology, the measurement of combustion field temperature and component concentration has the advantages of non-invasive passage through the interior of the combustion field, fast response time, and strong anti-electromagnetic interference ability. The measuring instrument and equipment system is easy to install in a relatively small space, and it is easy to install in the combustion site for monitoring the combustion state.

The signal receiving module used in the existing measuring instrument system uses an independent transmitting and receiving device. The disadvantage is that two sets of transmitting and receiving devices are built at the same time, the space utilization rate is low, and the increased transmitting and receiving device will affect the layout of the optical path. The optical path information in the entire temperature field cannot be fully obtained, resulting in low measurement accuracy.

SUMMARY OF THE INVENTION

The invention provides a device for reconstructing the temperature field of a combustion flame by scanning the optical path of the laser absorption spectrum, which solves the shortcomings of complex optical path arrangement and little effective information extraction of the optical path in the existing measuring device.

The technical scheme that the present invention adopts is as follows:

A device for reconstructing the temperature field of a combustion flame by scanning the optical path of a laser absorption spectrum, including a function generator, a laser controller, a distributed feedback laser, an optical fiber beam splitter, a hollow retroreflector, and signal processing components, as well as a reflector and a laser emitter The receiving device, the reflector, the laser emitting and receiving device correspond to the number of light beams modulated by the optical fiber beam splitter respectively; the optical fiber beam splitter divides the laser light modulated by the distributed feedback laser into multiple beams, and each beam consists of The corresponding laser emitting and receiving device emits to the corresponding reflector, and the reflector is driven to rotate by the driving mechanism and distributed in the space to ensure that the optical path sweeps the entire area to be measured, returns in parallel through the hollow retroreflector, and is The laser emitting and receiving device receives and converts the electrical signal to obtain the light intensity signal.

As a further improvement of the above technical solution:

The structure of the laser emitting and receiving device includes a collimator, a wedge prism and a photodetector arranged sequentially along the optical path to collimate the laser beam; One end of the mirror is coated with a semi-transparent and semi-reflective film corresponding to the wavelength band of the distributed feedback laser, and the other end of the mirror is coated with an anti-reflection film facing away from the collimator to ensure that the laser reflected by the hollow retroreflector can better enter the photodetector.

The wedge-shaped prism is a wedge-shaped structure with a trapezoidal cross-section, one side of which is inclined relative to the other corresponding side.

The wedge prism is a circular prism with one side inclined by 1° relative to the corresponding other side, the main purpose of which is to eliminate the interference effect of signals.

The bandwidth of the photodetector is 10MHz, and it is installed at the tail of the laser emitting and receiving device through a fixing frame. The laser light returned in parallel through the hollow retroreflector is received by the photodetector and converted into an electrical signal to obtain a light intensity signal.

The driving mechanism adopts a high-speed stepping motor, and each reflector is connected with the corresponding high-speed stepping motor, and is driven to rotate by the high-speed stepping motor.

Two of the laser controller and the distributed feedback laser are correspondingly arranged, and the function generator respectively inputs modulation signals into two distributed feedback laser controllers through two channels. The output wavelength and light intensity of the distributed feedback laser are modulated; the optical fiber beam splitter divides the modulated laser of the distributed feedback laser into four beams.

There are four laser emitting and receiving devices in total, which are respectively arranged at the four corners of the optical path. The arrangement position of the laser emitting and receiving devices ensures that the optical path passing through the hollow retroreflector is not blocked.

The signal processing component includes a signal acquisition system and a computer, and the light intensity signal is transmitted to the signal acquisition system by the corresponding laser emitting and receiving device, and processed by the computer.

The beneficial effects of the present invention are as follows:

The invention optimizes the measurement device and has a compact structure, realizes the integration of signal transmission and reception, reduces the number of measurement components, miniaturizes and integrates, can realize rapid reconstruction of the temperature field, can obtain more comprehensive optical path information, and improves measurement accuracy.

The laser emitting and receiving device of the present invention realizes the function of sending and receiving at the same time. One end face of the wedge-shaped prism can well prevent light from other wave bands from entering the detector and saturate the detector; the other end face ensures that the laser light reflected back by the hollow reflector can be more Good entry detector. The laser emitting and receiving device of the present invention can be arranged at the four corners of the optical path according to actual needs to ensure that the optical path passing through the hollow retroreflector is not blocked. The optical path structure is arranged more compactly.

The reflection mirror of the present invention is driven by a high-speed stepping motor to quickly obtain information in the optical path, thereby improving the time resolution of reconstructing the temperature field.

The parameters of each component of the device of the invention can establish a unified temperature field detection standard, which is repeatable, adjustable and operable.

Description of drawings

Fig. 1 is a structural schematic diagram of the measuring device of the present invention.

Fig. 2 is a structural schematic diagram of the laser emitting and receiving device of the present invention.

In the figure: 1. Function generator; 2. Laser controller; 3. Distributed feedback laser; 4. Optical fiber beam splitter; 5. Mirror; 6. High-speed stepping motor; 7. Laser transmitting and receiving device; Collimator; 702, wedge prism; 703, photoelectric detector; 704, fixed frame; 8, hollow retroreflector; 9, signal acquisition system; 10, computer.

Detailed ways

The specific embodiments of the present invention will be described below in conjunction with the accompanying drawings.

As shown in Figure 1, the device for reconstructing the temperature field of a combustion flame by scanning the optical path of the laser absorption spectrum in this embodiment includes a function generator 1, a laser controller 2, a distributed feedback laser 3, an optical fiber beam splitter 4, and a hollow retroreflector 8 and a signal processing assembly, also including a reflector 5, a high-speed stepping motor 6 and a laser transmitting and receiving device 7, the number of light beams modulated by the reflecting mirror 5, a high-speed stepping motor 6, the laser transmitting and receiving device 7 and the optical fiber beam splitter 4 Correspondingly; the optical fiber beam splitter 4 divides the laser modulated by the distributed feedback laser 3 into multiple beams, and each beam is transmitted from the corresponding laser transmitting and receiving device 7 to the corresponding mirror 5, and the mirror 5 is driven by a high-speed stepping motor 6 Drive the rotation, distribute in the space, ensure that the optical path sweeps the entire area to be measured, return in parallel through the hollow retroreflector 8, and be received by the laser emitting and receiving device 7 and converted into an electrical signal to obtain a light intensity signal.

As shown in Figure 2, the structure of the laser emitting and receiving device 7 includes a collimator 701, a wedge prism 702 and a photodetector 703 arranged in sequence along the optical path to collimate the laser beam;

Specifically, the laser emitting and receiving device 7 is the main device to realize the function of sending and receiving at the same time. The collimator 701 collimates the laser beam to ensure that the laser beam is not too divergent in the entire optical path structure to receive the light; the center of the laser emitting and receiving device 7 is a semi-transparent and semi-reflective coated wedge prism 702, which adopts a semi-transparent and semi-reflective coating wedge prism 702. The anti-prism can reflect 50% of the laser light through the area to be measured through the reflective surface, and this beam of laser light is reflected back by the hollow retro-reflector 8 in parallel and hits the target surface of the photodetector 703 through the semi-transparent and semi-reflective prism. The mirror at one end of the transflective prism close to the collimator 701 is plated with a transflective film corresponding to the wavelength band emitted by the distributed feedback laser 3, which can well prevent light from other bands from entering the photodetector 703 and saturate the photodetector 703. The anti-reflection coating is coated on the mirror surface of the half-reflective prism facing away from the collimator 701 to ensure that the laser light reflected by the hollow retroreflector 8 can better enter the photodetector 703 .

As an implementation manner, the wedge prism 702 is a circular prism whose one side is inclined relative to the other side, and the main purpose is to eliminate the interference effect of signals. Specifically, the section of the wedge prism 702 is a right-angled trapezoid, and the hypotenuse is inclined by 1° relative to the right-angled side. The photodetector 703 at the tail of the laser transmitting and receiving device 7 adopts a self-designed photodetector 703 with a bandwidth of 10 MHz. The entire photodetector 703 is fixed by a fixing frame 704 . The laser light returning in parallel through the hollow retroreflector 8 is received by the photodetector 703 and converted into an electrical signal to obtain a light intensity signal.

As an embodiment, each reflector 5 is connected with a high-speed stepping motor 6 and is driven to rotate by the high-speed stepping motor 6 . Reflector 5 also can adopt other drive, transmission mechanism to drive rotation.

The high-speed stepping motor 6 drives the mirror 5 to rotate, which can quickly obtain information in the optical path, thereby improving the time resolution of reconstructing the temperature field.

As an implementation mode, two laser controllers 2 and two distributed feedback lasers 3 are arranged correspondingly, and the function generator 1 respectively inputs modulation signals into two distributed feedback laser controllers 2 through two channels. 2. Modulating the output wavelength and light intensity of the corresponding distributed feedback laser 3;

As an implementation manner, the optical fiber beam splitter 4 divides the modulated laser light of the distributed feedback laser 3 into four beams.

As an implementation, there are four laser emitting and receiving devices 7 , which are respectively arranged at four corners of the optical path. Make the structure of the whole optical path more compact.

As an implementation, the signal processing component includes a signal acquisition system 9 and a computer 10 , the light intensity signals are transmitted to the signal acquisition system 9 by the corresponding laser emitting and receiving device 7 , and processed by the computer 10 .

The measurement method of the laser absorption spectrum scanning optical path reconstruction combustion flame temperature field of the present embodiment, based on the measurement device includes as shown in Figure 1 and Figure 2:

Function generator 1, two laser controllers 2, two distributed feedback lasers 3, fiber optic beam splitter 4, four laser transmitting and receiving devices 7, four mirrors 5 and corresponding stepping motors, hollow retroreflector 8. Signal acquisition system 9. Computer 10.

The function generator 1 inputs the modulation signal into the laser controller 2, and the laser controller 2 tunes the output wavelength and light intensity of the distributed feedback laser 3; it is divided into four beams by the optical fiber beam splitter 4, and each beam is transmitted and received by the laser. The device 7 transmits to the mirror 5, the mirror 5 is connected with the high-speed stepping motor 6, the stepping motor drives the mirror 5 to rotate, the optical path sweeps the area to be measured, returns in parallel through the hollow retroreflector 8, and is received by the laser emitting and receiving device 7 The photodetector 703 in the photoelectric signal is received and converted into an electrical signal to obtain a light intensity signal. Both the background signal and the transmission signal are transmitted to the signal acquisition system 9 by the corresponding photodetector 703 and processed by the computer 10 .

The measurement method specifically includes the following steps:

Step 1, the function generator 1 inputs the modulation frequency f _m1 signal into the No. 1 laser controller 2 through channel 1, and the No. 1 laser controller 2 tunes the output wavelength and light intensity of the No. 1 distributed feedback laser 3;

The function generator inputs the modulation frequency f _m2 signal into the No. 2 laser controller 2 through channel 2, and the No. 2 laser controller 2 tunes the output wavelength and light intensity of the No. 2 distributed feedback laser 3;

Step 2: Coupling the two beams of modulated light from Step 1, and splitting them into four beams through the optical fiber beam splitter 4, each beam is transmitted to the reflector 5 by the corresponding laser emitting and receiving device 7, and the reflector 5 follows the high-speed step The motor 6 rotates, the optical path sweeps across the area to be measured, returns in parallel through the hollow retroreflector 8, receives and converts it into an electrical signal through the photodetector 703 in the laser emitting and receiving device 7, and obtains a light intensity signal;

Step 3, through the optical etalon, respectively obtain the etalon signal I _v (t) corresponding to No. 1 and No. 2 distributed feedback laser 3, thereby obtaining the time-frequency response characteristic v (t);

Step 4: process the measured background light intensity and transmitted light intensity through digital phase-locking and low-pass filtering process, extract and subtract the background normalized second harmonic, according to the Beer-Lambert law, through the normalized second harmonic and The time-frequency response characteristic v(t) obtained in step 3 is used to fit the integrated absorption area A by using the least squares algorithm, and the temperature is measured according to the dual-wavelength line intensity ratio method, and the concentration value is further calculated;

Firstly, the digital phase-locking technology is used to process the background light intensity I ₀ (i) and the actual measured transmitted light intensity I _t (i), and the x-component and y-component expansion formulas of the i-th laser beam n-th harmonic of the signal are respectively obtained, and the expansion formula As shown in formula (1), where n takes the value of 1 or 2:

Secondly, the harmonic components of each signal are extracted through a low-pass filter, as shown in formula (2):

The obtained harmonic components of the i-th laser background light intensity signal and transmitted light intensity signal can be expressed as formula (3):

Finally, for the i-th laser harmonic signal obtained, the first harmonic normalization processing is performed to subtract the background to obtain the formula (4):

When the medium gas distribution on the measurement path is uniform, the average temperature and concentration on the path can be calculated by the following formula:

R为线强比值，是温度的单调函数。S(T) is the absorption line intensity of the gas, A is the integral absorption area, X is the volume fraction of the gas, L is the specific length of the measured optical path, P is the total pressure of the gas, the unit is atm, φ _v is a linear function , and after normalization

R is the line intensity ratio, which is a monotone function of temperature.

Step five, solving the two-dimensional transient temperature field.

Based on the measurement principle of two-dimensional tomographic reconstruction technology, in order to obtain the parameter information in the two-dimensional space of the measured area, the reconstruction area needs to be discretized. grid, assuming that the temperature and other parameters in each discrete grid are uniformly distributed.

After the i-th laser ray passes through the measurement area, the effective optical path length in each discrete grid is l _{i, j} , which is the path matrix of the laser ray. The specific value can be determined by the geometric relationship (the width of the discrete grid and the laser The angle α) between the ray and the coordinate axis is determined.

When the distribution of the medium gas on the path is uneven, the formula (5) is transformed, the light passes through the absorption of the medium gas in the discrete grid, and the intensity weakens when it leaves the measurement area, and the discretization of the two spectral lines in the i-th light is Absorption equation:

Among them, A _{v1, i} and A _{v2, i} are the path absorption integral value after the i-th ray passes through the measurement area, i is the number of the laser ray beam, j is the discrete grid number, α _{v1, j} and α _{v2, j} represents the gas absorption coefficient within each discrete grid.

Formula (11) and formula (12) are the specific discrete equations for two H2O absorption lines:

Among them, α _{v1, j} = (PS _T X) _{v1, j} and α _{v2, j} = (PS _T X) _{v2, j} is the absorption coefficient of the two absorption lines in the discrete grid, m is the total The number of rays, n is the total number of grids divided.

The ART algorithm can obtain ideal results in the reconstruction process based on incomplete projection values, so it is widely used in the reconstruction of two-dimensional combustion fields. For the ART algorithm, the solution process is performed ray by ray. When each ray is considered, the image is updated once, that is, an iteration is completed. If the image does not meet the convergence requirements, the above process will be is repeated until the convergence condition is satisfied.

When using the iterative algorithm to solve the two-dimensional temperature and concentration distribution, it is first necessary to solve the gas absorption coefficient α _{v1, j} and α _{v2, j} in the discrete grid. The specific expression of the absorption coefficient α _j calculated by the ART algorithm is as follows:

是通过重建迭代程序计算得到单个波长下每个离散网格内的气体吸收系数，λ为松弛因子，其具体取值在0～2之间，常用于提高收敛速度和获取较高的重建质量，k代表总的迭代循环次数。由公式(6)可知，两条吸收谱线线强的比值可以通过迭代求解得到的每个离散网格内的吸收系数α_v1，j和α_v2，j的比值求得，进而利用公式(7)计算得到每个网格内的温度值T_j。in,

The gas absorption coefficient in each discrete grid at a single wavelength is calculated through the reconstruction iterative program. λ is the relaxation factor, and its specific value is between 0 and 2. It is often used to improve the convergence speed and obtain higher reconstruction quality. k represents the total number of iteration cycles. It can be seen from formula (6) that the ratio of the two absorption spectral line intensities can be obtained by iteratively solving the ratio of the absorption coefficient α _v1,j and α _v2,j in each discrete grid, and then using the formula (7 ) to calculate the temperature value T _j in each grid.

Claims (7)

1. A device for reconstructing the temperature field of a combustion flame by scanning the optical path of a laser absorption spectrum, including a function generator (1), a laser controller (2), a distributed feedback laser (3), an optical fiber beam splitter (4), and a hollow loop Transmitter (8) and signal processing assembly, it is characterized in that, also comprise reflection mirror (5) and laser transmitting and receiving device (7), described reflecting mirror (5), laser transmitting and receiving device (7) and optical fiber beam splitter (4) The numbers of beams after modulation correspond to each other; The optical fiber beam splitter (4) divides the modulated laser light of the distributed feedback laser (3) into multiple beams, and each beam is transmitted to the corresponding mirror (5) by the corresponding laser transmitting and receiving device (7). ), the reflector (5) is driven to rotate by the driving mechanism, and is distributed in space to ensure that the optical path sweeps through the entire area to be measured, and returns in parallel through the hollow retroreflector (8), and is received by the laser emitting and receiving device ( 7) Receive and convert into an electrical signal to obtain a light intensity signal; The structure of the laser emitting and receiving device (7) includes a collimator (701), a wedge prism (702) and a photodetector (703) arranged sequentially along the optical path to collimate the laser beam; The wedge-shaped prism (702) is a semi-transparent and semi-reflective prism, and its end close to the collimator (701) is mirror-plated with a semi-transparent and semi-reflective film corresponding to the wavelength band of the distributed feedback laser (3), facing away from the One end of the collimator (701) is mirror-coated with an anti-reflection coating to ensure that the laser light reflected by the hollow retroreflector (8) can better enter the photodetector (703). 2. the device of laser absorption spectrum scanning light path reconstruction combustion flame temperature field according to claim 1, is characterized in that, described wedge prism (702) is the wedge-shaped structure that cross section is trapezoid, and its one side is inclined relative to the other side of correspondence set up. 3. the device of laser absorption spectrum scanning light path reconstruction combustion flame temperature field according to claim 1, it is characterized in that, the bandwidth of described photodetector (703) is 10M, is installed in laser emission receiving by fixed mount (704) At the tail of the device (7), the laser light returned in parallel through the hollow retroreflector (8) is received by the photodetector (703) and converted into an electrical signal to obtain a light intensity signal. 4. the device of laser absorption spectrum scanning optical path reconstruction combustion flame temperature field according to claim 1, is characterized in that, described driving mechanism adopts high-speed stepper motor (6), and each reflecting mirror (5) is connected with corresponding The high-speed stepping motor (6) is connected to each other, and is driven to rotate by the high-speed stepping motor (6). 5. The device of laser absorption spectrum scanning optical path reconstruction combustion flame temperature field according to claim 1, characterized in that, the laser controller (2) and the distributed feedback laser (3) are respectively arranged with two , the function generator (1) respectively inputs the modulation signal into two distributed feedback laser controllers (2) through two channels, and the laser controller (2) controls the corresponding distributed feedback laser (3) The output wavelength and light intensity are modulated; the optical fiber beam splitter (4) divides the modulated laser light from the distributed feedback laser (3) into four beams. 6. the device of laser absorption spectrum scanning optical path reconstruction combustion flame temperature field according to claim 5, is characterized in that, described laser emission receiving device (7) is provided with four altogether, is arranged in four corners of optical path respectively, The arrangement position of the laser emitting and receiving device (7) ensures that the light path passing through the hollow retroreflector (8) is not blocked. 7. the device of laser absorption spectrum scanning optical path reconstruction combustion flame temperature field according to claim 1, is characterized in that, described signal processing assembly comprises signal acquisition system (9) and computer (10), and described light intensity signal is The signal is transmitted to the signal acquisition system (9) by the corresponding laser emitting and receiving device (7), and processed by the computer (10).

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