CN115452768A - Three-dimensional temperature, gas concentration and particle concentration distribution measurement system in turbulent combustion field - Google Patents

Abstract

The invention discloses a three-dimensional temperature, gas concentration and particle concentration distribution measuring system of a turbulent combustion field, comprising: an _H2O laser emitting two _H2O molecular infrared absorption lines; a _CO2 laser emitting _CO2 molecular infrared absorption spectral line; a beam splitter, which divides the absorption spectral line into multiple laser beams distributed in a grid in the combustion field to be measured; a photodetector, arranged around the combustion field to be measured, for receiving the laser beam; a mobile platform , to drive the beam splitter and photodetector to move; the upper computer system obtains the temperature, CO ₂ gas concentration and particle concentration of each grid in the two-dimensional plane through algebraic iteration; and then obtains through multiple two-dimensional plane reconstruction Three-dimensional temperature, _CO2 gas concentration and particle concentration of the combustion field to be measured. The invention simultaneously reconstructs the three-dimensional temperature, CO ₂ gas concentration and particle concentration of the turbulent combustion field online, and has the advantages of non-invasiveness, fast response and high sensitivity.

Description

Three-dimensional temperature, gas concentration and particle concentration distribution measurement system in turbulent combustion field

technical field

The invention relates to the field of combustion field measurement, in particular to a three-dimensional temperature, gas concentration and particle concentration distribution measurement system of a turbulent combustion field.

Background technique

The combustion of fossil fuels is the most important form of energy utilization in the world today, supporting the industrial operation and social development of human society. In actual combustion equipment, turbulent combustion is the main form of combustion. Due to the complexity of the turbulent combustion field, the spatial distribution of the temperature, gas components and soot particle concentration in the combustion flame is not uniform, and the distribution of these key physical parameters and chemical product concentrations will affect the combustion process. Energy conversion efficiency and safety have an impact. At the same time, pollutants such as soot particles produced by incomplete combustion will cause serious environmental problems and threaten human safety and health.

In order to control the emission of soot pollutants during turbulent combustion, a good understanding of its generation mechanism is required. The temperature and CO ₂ concentration in the flame all have a great influence on the formation of soot, but the specific mechanism of action is still controversial. In addition, the temperature of the turbulent combustion field and the concentration of CO ₂ as one of the important products of the combustion process are also of great significance to the basic research of combustion reactions. These theoretical studies on turbulent combustion science require related technologies to accurately measure the three-dimensional distribution of flame temperature, gas component concentration and soot concentration on-line.

Chinese patent CN 111141524 A is based on tunable semiconductor laser absorption spectroscopy technology, designed a gas parameter measurement device in the combustion field, and arranged a fan-shaped beam to cover the reconstruction area, but the system only realized two-dimensional analysis of a single gas in the combustion flow field. Dimensional reconstruction.

Chinese patent CN 113310857 A designs a system that uses tomographic laser-induced incandescent light to measure the primary particle size distribution of soot particles in a combustion field, and uses an emission spectrum tomography colorimetric temperature measurement system to measure the turbulent flame temperature field. However, when using laser-induced incandescent light to measure particle concentration, it is necessary to first measure and calibrate a standard flame with known soot particle concentration, which increases the complexity of the system and operation. In addition, the system does not realize the measurement of the concentration field of combustion gas products.

Therefore, how to simultaneously measure the three-dimensional distribution of multiple parameters such as the temperature of the turbulent combustion field, the concentration of _CO2 gas, and the concentration of particles is of great importance to the basic research of combustion science, the improvement of combustion efficiency, and the control of pollutant emissions. significance.

Contents of the invention

In order to solve at least one technical problem mentioned in the background technology, the object of the present invention is to provide a kind of turbulent combustion field three-dimensional temperature, gas concentration, particle concentration distribution measurement system, the three-dimensional temperature of turbulent combustion field, _CO gas concentration and particle concentration Concentration can be reconstructed online at the same time, which has the advantages of non-invasiveness, fast response and high sensitivity.

In order to achieve the above object, the present invention provides the following technical solutions: a three-dimensional temperature, gas concentration, and particle concentration distribution measurement system in a turbulent combustion field, including:

H ₂ O laser, used to emit two infrared absorption lines of H ₂ O molecules;

_CO2 lasers for emitting infrared absorption lines of _CO2 molecules;

The beam splitter is used to divide the infrared absorption line of H ₂ O molecules or the infrared absorption line of CO ₂ molecules into multiple laser beams distributed in a grid in a certain two-dimensional plane of the combustion field to be measured;

a photodetector, arranged around the combustion field to be measured, for receiving the laser beam;

a mobile platform, driving the beam splitter and the photodetector to move along a direction perpendicular to the two-dimensional plane;

The upper computer system solves the temperature, CO 2 gas concentration and particle concentration on each laser beam in the two-dimensional plane, and obtains the temperature, CO ₂ gas concentration and particle concentration of each grid in the _two -dimensional plane through algebraic iteration; Then the three-dimensional temperature, _CO2 gas concentration and particle concentration of the combustion field to be measured are obtained through multiple two-dimensional plane reconstructions.

Further, the solution process of the temperature is as follows:

Construct the relationship between spectral line intensity and temperature:

Among them, k is Boltzmann's constant, h is Planck's constant, c is the speed of light, S(T ₀ ) represents the spectral line intensity of the gas absorption line at the reference temperature T ₀ , E″ represents the transition frequency v ₀ The low-state transition energy of , Q(T) represents the partition function of the absorbing gas at temperature T, and Q(T ₀ ) represents the partition function of the absorbing gas at the reference temperature T ₀ ;

The partition function is:

Q(T)＝a+bT+cT ² +dT ³

Among them, a, b, c, d are the third-order polynomial coefficients of the partition function;

When scanning the two infrared absorption lines v ₁ and v ₂ of H ₂ O molecules, the temperature can be obtained:

Among them, S(T) _v1 is the spectral line intensity of the v ₁ absorption line of _H2O at temperature T, and S(T _{) v2} is the spectral line intensity of the v2 absorption line of _H2O at temperature T, S(T ₀ ) _v1 is the spectral line intensity of the v ₁ absorption line of H ₂ O at the reference temperature T ₀ , S(T ₀ ) _v2 is the v ₂ absorption line intensity of H ₂ O at the reference temperature T ₀ spectral line intensity.

Further, the solution process of the _CO2 gas concentration is as follows:

Construct the raycast intensity formula:

表示气体吸收谱线的线型函数，S(T)表示气体吸收谱线在温度T下的谱线强度；线型函数

在整个光谱范围内的积分值为1。Among them, I ₀ represents the incident laser intensity, I _t represents the outgoing laser intensity, L represents the optical path, α _abs represents the gas absorption coefficient, κ _ext represents the particle extinction coefficient, E _flame represents the flame radiation intensity, P represents the air pressure, and X _abs represents the absorption gas concentration,

Represents the linear function of the gas absorption line, S(T) represents the spectral line intensity of the gas absorption line at temperature T; the linear function

The integral value is 1 over the entire spectral range.

Further, the solution process of the particle concentration is as follows:

Among them, f _v is the particle concentration; λ is the laser incident wavelength, m is the negative refractive index; κ _abs is the absorption coefficient of the particle.

Further, the algebraic iteration process of the gas absorption coefficient is as follows:

The optical path of the j-th beam passing through the i-th grid is denoted as L _i,j , and the equation A=∑α _abs L is solved, then the projected absorbance A _vm,j of the j-th beam passing through the entire area to be measured is expressed as :

Among them, the subscript vm represents the beam with the wavelength v _m , and _αi represents the absorbance per unit length in a single grid. In the iterative algorithm, the absorbance per unit length in each grid of the K-th iteration is expressed as:

The iterative process stops when the difference between two adjacent iterative processes α _{vm, i} is less than ε, expressed as the following formula;

Further, a time-division multiplexer is arranged in front of the beam splitter, and the time-division multiplexer alternately outputs the infrared absorption lines of H ₂ O molecules and the infrared absorption lines of CO ₂ molecules in time sequence.

Further, the output end of the beam splitter is provided with a laser collimator, and the laser collimator is used to collimate the split laser beam.

Further, a heat insulating sleeve is arranged outside the photodetector and/or the laser collimator.

Further, the host computer system includes a data acquisition card and a computer.

Compared with prior art, the beneficial effect of the present invention is:

Based on the molecular absorption spectrum, the present invention proposes to simultaneously measure and separate the molecular absorption coefficient and the soot extinction when considering the absorption of gas molecules in the turbulent combustion field, the extinction of soot and the flame background radiation acting together on the laser signal. The new method of the coefficient; then the algebraic iterative reconstruction algorithm is used to finally obtain the three-dimensional distribution of temperature, CO ₂ gas concentration and particle concentration, which has the advantages of non-invasive, fast response and high sensitivity.

Description of drawings

FIG. 1 is an overall schematic block diagram of an embodiment of the present invention.

FIG. 2 is a schematic diagram of signals of two signal generators in one cycle of the present invention.

Fig. 3 is a schematic flowchart of an embodiment of the present invention.

In the figure: 1. H ₂ O laser; 1a, first signal generator; 2. CO ₂ laser; 2a, second signal generator; 3. beam combiner; 4. time division multiplexer; 5. beam splitter ; 6. Laser collimator; 7. The first heat insulation sleeve; 8. Photoelectric detector; 9. The second heat insulation sleeve; 10. Signal amplification integration device; 11. Data acquisition card; 12. Computer.

detailed description

The following clearly and completely describes the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Please refer to FIG. 1 , this embodiment provides a three-dimensional temperature, gas concentration, and particle concentration distribution measurement system in a turbulent combustion field. Including: laser system, emission and reception measurement system, signal detection and acquisition system, three-dimensional mobile platform.

Specifically, the laser system includes: a first signal generator 1a, a second signal generator 2a, an H ₂ O laser 1 (a distributed feedback tunable semiconductor laser operating at 1398.3nm for H ₂ O detection), a CO ₂ Laser 2 (distributed feedback tunable semiconductor laser used for _CO2 detection and working at 2001.6nm), beam combiner 3, time division multiplexer 4, beam splitter 5; the beam splitter 5 makes _H2O molecules infrared Absorption lines or infrared absorption lines of CO ₂ molecules are respectively divided into multiple laser beams distributed in a grid in a certain two-dimensional plane of the combustion field to be measured.

The transmitting and receiving measurement system includes: a laser collimator 6 , a first temperature-insulating sleeve 7 , a combustion field S to be measured, a photoelectric detector 8 , and a second temperature-insulating sleeve 9 . The function of the first temperature insulation sleeve 7 and the second temperature insulation sleeve 9 is to reduce the radiation influence of the turbulent combustion field to be measured.

The signal detection and acquisition system includes: a signal amplification integration device 10 and a host computer system; the host computer system includes a data acquisition card 11 and a computer 12 .

The three-dimensional mobile platform includes: a mobile platform, which drives the beam splitter and the photodetector to move along a direction perpendicular to the two-dimensional plane.

When working, the first signal generator 1a generates a sawtooth wave signal and a square wave signal in one period, and superimposes the signal to the laser controller A. The superposition of the sawtooth wave signal makes the H ₂ O laser 1 (1398.3nm) in Continuous scanning in a narrow band range, the corresponding driving current after superimposing the square wave signal is lower than the laser threshold current, so that the laser has no output signal in this segment, that is, the laser output signal is 0. A laser controller superimposed with a sawtooth wave signal drives an H ₂ O laser (1398.3nm), which can simultaneously scan two infrared absorption lines of H ₂ O molecules.

The second signal generator 2a generates a section of sawtooth wave signal and a section of square wave signal in one period, and superimposes the signal to the laser controller B. The superposition of the sawtooth wave signal makes the _CO2 laser 2 (2001.6nm) in a narrow band range Continuous scanning, the corresponding driving current after superimposing the square wave signal is lower than the laser threshold current, so that the laser has no output signal in this period, that is, the laser output signal is 0. The laser controller superimposed with the sawtooth wave signal drives the _CO2 laser (2001.6nm), which can scan a single _CO2 molecular infrared absorption line for _CO2 concentration measurement. The signals of the two signal generators in one cycle are shown in Figure 2 Show.

After the two laser beams are output through the pigtails, they are combined by the beam combiner 3, then passed through the time division multiplexer 4, and finally the beams are divided into 18 paths by the beam splitter 5. Among them, 9 beams are collimated by the laser collimator 6 on the right side of the combustion field S to be measured, and 9 beams are collimated by the laser collimator 6 on the lower side of the combustion field S to be measured. After the 18 light beams pass through the flow field area together, they are respectively received by 18 photodetectors 8 .

The detection signal of the photodetector 8 is further amplified by the signal amplification integration device 10. The multi-signal amplification integration device 10 includes a first-stage transimpedance amplifier and a second-stage signal amplifier. By adjusting the resistance of the two-stage amplifiers, the final signal amplification is realized. The data acquisition card collects the amplified signal synchronously, and then transmits it to the computer for data processing on the collected signal.

Before the operation of the combustion field S to be tested, the data acquisition card can obtain the laser background signal. After the burner to be tested is ignited, the data acquisition card can simultaneously obtain H ₂ O molecular absorption signals, CO ₂ molecular absorption signals, particle absorption signals and flame background radiation signals within one cycle. The data from the acquisition card is transmitted to the computer, and the molecular absorption coefficient and soot extinction coefficient are separated, and the H ₂ O molecular absorbance, CO ₂ molecular absorbance and soot extinction coefficient of each optical path can be obtained at the same time.

Divide the _{two -} dimensional area of each layer of the burner to be tested into a total of 81 grids of 9×9, and use the algebraic iterative method to obtain The temperature distribution of the combustion field, the CO ₂ gas concentration distribution and the two-dimensional distribution of the soot particle concentration are solved, and the nine-layer two-dimensional area is reconstructed by moving the mobile platform along the third dimension, and a total of 729 grids of 9×9×9 are established The temperature distribution, CO ₂ gas concentration distribution and soot particle concentration distribution in the spatial coordinate system, and then realize the online measurement of the three-dimensional temperature, CO ₂ gas concentration and particle concentration of the turbulent combustion field. The flow chart of the multi-parameter three-dimensional measurement system is shown in Figure 3 Show.

Raycast Intensity Formula:

表示气体吸收谱线的线型函数，S(T)表示气体吸收谱线在温度T下的谱线强度。其中，线型函数

在整个光谱范围内的积分值为1，谱线强度S_T只与温度、谱线位置有关，可以表示为：In the formula, I ₀ represents the incident laser intensity, I _t represents the outgoing laser intensity, L represents the optical path, α _abs represents the gas absorption coefficient, κ _ext represents the particle extinction coefficient, E _flame represents the flame radiation intensity, P represents the pressure, and X _abs represents The concentration of the absorbed gas,

Represents the linear function of the gas absorption line, and S(T) represents the line intensity of the gas absorption line at temperature T. Among them, the linear function

The integral value in the entire spectral range is 1, and the spectral line intensity S _T is only related to temperature and spectral line position, which can be expressed as:

Among them, k is Boltzmann's constant, h is Planck's constant, c is the speed of light, S(T ₀ ) represents the spectral line intensity of the gas absorption line at the reference temperature T ₀ , E″ represents the transition frequency v ₀ The low-state transition energy of , Q(T) represents the partition function of the absorbing gas at temperature T, and Q(T ₀ ) represents the partition function of the absorbing gas at the reference temperature T _0. The partition function can be simplified as a third-order polynomial with respect to temperature ,Expressed as:

Q(T)＝a+bT+cT ² +dT ³

For H ₂ O molecules and CO ₂ molecules, the third-order polynomial coefficients of the partition function in the range of low temperature 70-500K, medium temperature 500-1500K, and high temperature 1500-3005K are shown in Table 1.1 and Table 2.2, respectively.

Table 1.1 The third-order polynomial coefficients of the partition function of H ₂ O molecules at different temperatures

Table 2.1 Third-order polynomial coefficients of the partition function of _CO2 molecule at different temperatures

According to the temperature measurement by the double-line method, when scanning the two absorption lines v ₁ and v ₂ of H ₂ O, the temperature can be obtained, expressed as:

S(T) _v1 is the line intensity of the v ₁ absorption line of H ₂ O at temperature T, S(T) _v2 is the line intensity of the v ₂ absorption line of H ₂ O at temperature T, S( T ₀ ) _v1 is the spectral line intensity of the v ₁ absorption line of H ₂ O at the reference temperature T ₀ , S(T ₀ ) _v2 is the spectral line of the v ₂ absorption line of H ₂ O at the reference temperature T ₀ strength.

According to the Rayleigh hypothesis, when calculating the extinction coefficient κ _ext , only the absorption of particles is considered, and the effects of scattering and reflection on the laser intensity are ignored, that is, the extinction coefficient of particles is assumed to be κ _ext ≈ κ _abs , and κ _abs is the absorption coefficient of particles. The particle concentration f _v can be expressed as:

In the formula, λ is the laser incident wavelength, and m is the negative refractive index.

Due to the selectivity of gas absorption, it only exists in a narrow range of wavelengths within the laser wavelength scanning range, while the extinction of particles is ubiquitous in the entire laser wavelength scanning range. In addition, the flame radiation signal is an inherent attribute of the flame, and has nothing to do with whether there is laser output. Therefore, when the laser output signal is 0, the measured signal is the flame radiation intensity; when the laser output signal is normal and the sawtooth signal is superimposed, the gas absorption signal and the particle extinction signal are simultaneously detected and effectively separated.

In order to realize the three-dimensional solution, the three-dimensional space is firstly divided into nine two-dimensional spaces along the third dimension, and each two-dimensional space is solved separately. In each two-dimensional space, it is divided into 9×9 grids, and it is assumed that the physical parameters in each grid are the same. Solve the equations A=∑α _abs L and K=∑κ _abs L by means of algebraic iteration to obtain α _abs and κ _abs in each grid, and then obtain the α _abs in each grid from the α abs in each grid The temperature and gas concentration of , the particle concentration in each grid can be obtained from the κ _abs in each grid.

Divide the two-dimensional area into N×N grids, assuming that the physical parameters such as pressure, temperature, and concentration of the gas in each grid are the same. The optical path of the j-th beam passing through the i-th grid is denoted as L _i,j , and the equation A=∑α _abs L is solved, then the projected absorbance A _vm,j of the j-th beam passing through the entire area to be measured can be expressed for:

Among them, the subscript _vm indicates the beam with wavelength vm, and _αi indicates the absorbance per unit length in a single grid. In the iterative algorithm, the absorbance per unit length in each grid of the Kth iteration can be expressed as:

The iterative process stops when the difference of α _{vm, i} between two adjacent iterative processes is less than ε, which is expressed as the following formula. The iterative stop criterion chosen in this paper is ε=1.0×10 ^-10 .

The process of solving K=∑κ _abs L is similar to the process of solving equation A=∑α _abs L, as follows:.

The iterative process stops when the difference of α _{vm, i} between two adjacent iterative processes is less than ε, which is expressed as the following formula. The iterative stop criterion chosen in this paper is ε=1.0×10 ^-10 .

It will be apparent to those skilled in the art that the invention is not limited to the details of the above-described exemplary embodiments, but that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Accordingly, the embodiments should be regarded in all points of view as exemplary and not restrictive, the scope of the invention being defined by the appended claims rather than the foregoing description, and it is therefore intended that the scope of the invention be defined by the appended claims rather than by the foregoing description. All changes within the meaning and range of equivalents of the elements are embraced in the present invention.

Claims (9)

1. Turbulent combustion field three-dimensional temperature, gas concentration, granule concentration distribution measurement system, its characterized in that includes:

H ₂ o laser for emitting two H beams ₂ O molecule infrared absorption spectrum line;

CO ₂ laser for emitting CO ₂ Molecular infrared absorption lines;

beam splitter, let H ₂ O molecule infrared absorption spectrum line or CO ₂ The molecular infrared absorption spectral lines are respectively divided into a plurality of paths of laser beams which are distributed in a grid manner in a certain two-dimensional plane of a combustion field to be measured;

the photoelectric detector is arranged around the combustion field to be detected and used for receiving the laser beam;

the moving platform drives the beam splitter and the photoelectric detector to move along the direction vertical to the two-dimensional plane;

the upper computer system is used for solving the temperature and CO on each laser beam in a two-dimensional plane ₂ The gas concentration and the particle concentration are obtained by means of algebraic iteration to obtain the temperature and CO of each grid in a two-dimensional plane ₂ Gas concentration and particle concentration; then, three-dimensional temperature and CO of the combustion field to be measured are obtained through reconstruction of a plurality of two-dimensional planes ₂ Gas concentration and particle concentration.

2. The turbulent combustion field three-dimensional temperature, gas concentration, particle concentration distribution measurement system of claim 1, wherein the temperature solution is as follows:

and (3) establishing a relation between the spectral line intensity and the temperature:

where k is Boltzmann 'S constant, h is Planckian' S constant, c is the speed of light, S (T) ₀ ) Indicating the gas absorption line at a reference temperature T ₀ Line intensity at E' represents transition frequency v ₀ The transition energy of the low state, Q (T) represents the partition function of the absorption gas at the temperature T, Q (T) ₀ ) Indicating the absorption gas at a reference temperature T ₀ A lower partition function;

the partition function is:

Q(T)＝a+bT+cT ² +dT ³

wherein a, b, c and d are third-order polynomial coefficients of a partition function;

scanning two lines H ₂ O molecule infrared absorption line v ₁ And v ₂ Then, the temperature can be found:

wherein, S (T) _v1 Is H ₂ V of O ₁ Line intensity of absorption lines at temperature T, S (T) _v2 Is H ₂ V of O ₂ Line intensity of absorption line at temperature T, S (T) ₀ ) _v1 Is H ₂ V of O ₁ Absorption line at reference temperature T ₀ Line intensity at, S (T) ₀ ) _v2 Is H ₂ V of O ₂ Absorption line at reference temperature T ₀ The line intensity below.

3. The turbulent combustion field three-dimensional temperature, gas concentration, particle concentration distribution measurement system of claim 2, wherein the CO ₂ The solution process for the gas concentration is as follows:

constructing a ray projection intensity formula:

wherein, I ₀ Denotes the incident laser intensity, I _t Indicating the intensity of the emitted laser light, L the optical path, alpha _abs Denotes the gas absorption coefficient,. Kappa. _ext Denotes the extinction coefficient of the particles, E _f1ame Indicating flame radiation intensity, P air pressure, X _abs Which is indicative of the concentration of the absorbing gas,

a linear function representing the gas absorption line, S (T) representing the line intensity of the gas absorption line at a temperature T; linear function of

The integral value over the entire spectral range is 1.

4. The turbulent combustion field three-dimensional temperature, gas concentration, particle concentration distribution measurement system of claim 3, wherein the particle concentration is solved as follows:

wherein f is _v Is the particle concentration; λ is the laser incident wavelength, and m is the negative refractive index; kappa _abs Is the absorption coefficient of the particles.

5. The turbulent combustion field three-dimensional temperature, gas concentration, particle concentration distribution measurement system of claim 3, wherein the algebraic iterative process of gas absorption coefficients is as follows:

the optical path length of the jth beam through the ith grid is denoted as L _i,j Solving equation A = ∑ α _abs L, then the projection absorbance A of the jth light beam passing through the whole area to be measured _vm,j Expressed as:

wherein the subscript vm denotes a wavelength v _m A beam of (a) _i Represents the absorbance per unit length within a single grid, and in the iterative algorithm, the absorbance per unit length within each grid of the kth iteration is represented as:

the iterative process passes through two adjacent iterative processes alpha _vm,i Stops when the difference of (d) is less than epsilon, and is expressed as the following formula;

6. the turbulent combustion field three-dimensional temperature, gas concentration and particle concentration distribution measuring system according to claim 1, wherein a time division multiplexer is arranged in front of the beam splitter and alternately outputs the H in time sequence ₂ Infrared absorption line of O molecule and CO ₂ Molecular infrared absorption lines.

7. The turbulent combustion field three-dimensional temperature, gas concentration and particle concentration distribution measuring system as recited in claim 1, wherein the output end of the beam splitter is provided with a laser collimator for collimating the split laser beam.

8. The turbulent combustion field three-dimensional temperature, gas concentration, particle concentration distribution measurement system of claim 7, wherein the photodetector and/or laser collimator is externally provided with a thermal insulating sleeve.

9. The turbulent combustion field three-dimensional temperature, gas concentration, particle concentration distribution measurement system of claim 1, wherein the upper computer system comprises a data acquisition card and a computer.

Images