A method and system for measuring gas temperature in a Rayleigh scattering combustion field based on gas sampling analysis

Abstract

The application provides a Rayleigh scattering combustion field gas temperature measurement method based on gas sampling analysis, belongs to the technical field of optical measurement, and is used for standard flame combustion field gas temperature measurement. Compared with a traditional contact type flame temperature measurement method, the Rayleigh scattering method does not affect the flame characteristics and has high precision and high resolution. Existing Rayleigh scattering flame temperature measurement methods generally need simulation software to obtain the component concentration of each substance in the combustion field, but the data obtained through simulation may deviate from the actual situation. The application adopts a gas sampling method to obtain the component concentration of each substance in the combustion field, so that the obtaining of the component concentration of each substance in the combustion field no longer depends on simulation software. In specific measurement, a gas sampling bottle is connected to a sampling point through a sampling valve for sampling, and then the gas sampling bottle is connected to a gas analyzer for component concentration analysis of each substance. In addition, the technology is calibrated by a platinum resistance in a normal temperature air environment before measurement, so that the non-contact temperature measurement result is directly traced to the temperature standard ITS-90. The method realizes complete measurement of the combustion field gas temperature and has wide application prospects in standard flame measurement.

Description

(I)TECHNICAL FIELD

[0001] The application provides a Rayleigh scattering combustion field gas temperature measurement method and system based on gas sampling analysis, and belongs to the technical field of optical measurement. The method and system combine gas sampling analysis and Rayleigh scattering, eliminate the uncertainty and error caused by the simulation analysis of the combustion field gas concentration, realize complete measurement of the combustion field gas temperature, and use a platinum resistance to measure the room temperature. The Rayleigh scattering temperature measurement in the normal temperature air environment before measurement is calibrated by the platinum resistance, so that the non-contact temperature measurement result is directly traced to the temperature standard ITS-90. (II)BACKGROUND

[0002] Rayleigh scattering is an elastic light scattering phenomenon, which is generated when light interacts with particles (such as gas molecules or microparticles) smaller than its wavelength. The intensity of the scattered light is related to the wavelength of the incident light, the concentration of the particles and the temperature.

[0003] Traditional contact measurement of flame temperature needs to directly contact the flame, which will interfere with the combustion process and affect the flow field, chemical reaction and temperature distribution of the flame. The existing Rayleigh scattering flame temperature measurement method generally needs simulation software to obtain the component concentration of each substance in the combustion field. The data obtained by simulation may deviate from the actual situation. The application adopts a method combining gas sampling analysis and Rayleigh scattering temperature measurement to obtain the component concentration of each substance in the combustion field, so that the acquisition of the component concentration of each substance in the combustion field no longer depends on simulation software. The room temperature is measured by using a calibrated platinum resistance, and then the room temperature in the same environment is measured by using Rayleigh scattering technology. The scattered light signal is recorded, and the relationship between the Rayleigh scattering temperature measurement system and the standard temperature is established through multiple comparison measurements, so as to realize the traceability of the temperature standard ITS-90. (III)SUMMARY

[0004] In view of the problems of low spatial resolution, influence on the flow field and temperature distribution of the flame and the like of the traditional flame measurement method, the application provides a Rayleigh scattering temperature measurement method and system. The component concentration of each substance in the flame is obtained by using a gas sampling method, so that the acquisition of the component concentration of each substance in the Rayleigh scattering temperature measurement process no longer depends on simulation software such as Gaseq. The traceability of ITS-90 is realized by using platinum resistance calibration.

[0005] The system is composed of a laser light source, a chopper, an aperture, a sleeve, a half-wave plate, a high-power laser polarization beam splitter prism, a darkroom, a McKenna burner, a displacement table, a power meter and a probe, a convex lens, a filter, a photomultiplier tube, a collection system, an upper computer, a digital multimeter, a four-wire platinum resistance, a gas sampling bottle, and a gas analyzer. The laser continuously emits laser light, which is modulated into intermittent pulse signals by an optical chopper, and then the laser light is locked by an aperture, a sleeve, and other devices. Subsequently, the laser light passes through a half-wave plate and a high-power laser polarization beam splitter prism to divide into P-polarized light and S-polarized light, which then enters the darkroom through a coaxial light path and reaches the flame area of the McKenna burner. The Rayleigh scattering signal of the flame of the McKenna burner is collected by a convex lens imaging system and then converges onto a receiving device, i.e., a photomultiplier tube. A 532nm filter is placed in front of the photomultiplier tube to filter out non-Rayleigh scattering signals. The received signals are uploaded to the upper computer through the collection system. The signal demodulation is realized in the upper computer, and the optical signal value in the flame temperature field is output. The component concentrations of each substance in the flame temperature field are obtained using a gas analyzer. The Rayleigh scattering cross sections of each substance at different concentrations are obtained by consulting data and calculating. The flame temperature value is obtained by formula calculation and iteration. During the entire process, the power meter is used to monitor the laser power. The specific measurement steps are as follows:

[0006] Step one: the method and system for measuring the temperature of a Rayleigh scattering combustion field based on gas sampling analysis according to claim 1, characterized in that the room temperature is measured by a platinum resistance, and the Rayleigh scattering temperature measurement in the normal temperature air environment before measurement is calibrated by the platinum resistance, so that the non-contact temperature measurement result is directly traced to the basic definition of the temperature standard ITS-90; first, the laser is started for preheating, the room temperature of the experimental area is measured by the calibrated four-wire platinum resistance, the resistance value of the platinum resistance is read by a digital multimeter, the read resistance value is compared with the scale table of Pt100, and the room temperature T1 at the beginning of the experiment is recorded; after preheating, the laser is turned on, the continuous laser emitted by the laser is modulated into an intermittent pulse signal by an optical chopper, the modulated laser is constrained in diameter by a sleeve, an aperture and other devices, unnecessary stray light in the optical system is shielded at the same time, and the signal-to-noise ratio is improved; then the laser passes through a half-wave plate and a high-power laser polarization beam splitter prism, the half-wave plate introduces phase delay by changing the polarization direction of light through linearly polarized light, the polarization beam splitter separates the light beam into P-polarized light and S-polarized light according to the polarization state of light, the P-polarized light is transmitted, and the S-polarized light is reflected, the combination of the two can accurately control the polarization direction of the incident laser, optimize the scattered light, and improve the signal-to-noise ratio of the experiment; during the experiment, the polarization direction of the laser is adjusted by rotating the half-wave plate, so that the S-polarized light perpendicular to the direction of the optical path reaches the maximum value, and the intensity of the Rayleigh scattering light received by the receiving device is improved; then the scattered light of the laser is converged on a photomultiplier tube through the imaging system of the receiving device, there is a filter in front of the photomultiplier tube for filtering, which can effectively filter out unnecessary spectral components and only leave the Rayleigh scattering light of 532 nm, ensuring the accuracy of temperature measurement, and the signal received by the photomultiplier tube at room temperature is recorded as S(T1):

[0007]

[0008] Finally, the laser passes through the darkroom and irradiates the rake surface of the power meter probe, and the real-time power of the laser is monitored by the power meter to observe the stability of the laser.

[0009] Step two: the method and system for measuring the temperature of the Rayleigh scattering combustion field based on gas sampling analysis according to claim 1, characterized in that the real-time analysis of the concentration of each substance in the flame is realized through the gas sampling bottle and the gas analyzer, which eliminates the situation that the concentration of the substance obtained by the Gaseq simulation software may not be consistent with the actual situation, making the temperature calculation process more convincing; first, open the nitrogen valve, and after a period of time, open the propane and air cylinders, control the flow of the two gases through the flow control system to achieve a specific equivalence ratio, ignite after the gas valve is opened, and move the displacement table until the center plane of the photomultiplier tube is flush with the leftmost end of the burner head, and the surface of the burner head is 20 mm away from the laser. The signal acquisition of the sampling point is realized through the acquisition system and the upper computer, and the flame light signal collected at this time is recorded as S(T2):

[0010]

[0011] The relationship between temperature and signal can be obtained after simplifying the ideal gas law formula as follows:

[0012]

[0013] Connect the gas sampling bottle to the sampling point through the sampling valve, open the sampling valve to ensure that the gas can flow smoothly into the sampling bottle, and exhaust the sampling bottle before sampling to ensure that the air or residual gas in the sampling bottle is removed. After sampling is completed, connect the sampling bottle to the sampling analyzer to obtain the concentration of each component of the sampling point, and the Rayleigh scattering cross section of the flame can be obtained:

[0014]

[0015] X i is the concentration of each component, is the Rayleigh scattering cross section of the flame. Substitute the above values into formula (3) to obtain the flame temperature at the sampling point. After the signal acquisition is completed, move the displacement table 2 mm to the left, repeat the above steps, and until the photomultiplier tube cannot receive the Rayleigh scattering signal in the flame field. At this time, the flame temperature distribution on the horizontal plane 20 mm away from the burner head is obtained. (Four) Description of Drawings

[0016] Figure 1The whole structure schematic diagram of the Rayleigh scattering combustion field gas temperature measurement method and system based on gas sampling analysis is composed of the following parts: laser light source (1), optical chopper (2), diaphragm (3), half-wave plate (4), high-power laser polarization beam splitter prism (5), darkroom (6), displacement table (7), McKenna burner (8), displacement table controller (9), power meter probe (10), power meter (11), convex lens (12), optical filter (13), photomultiplier tube (14), acquisition system (15), upper computer (16), four-wire platinum resistance (17), digital multimeter (18), compressed air (19), propane (20), nitrogen (21), air pump (22), gate valve (23), flow meter (24), flow control system (25), fuel gas sampling bottle (26), fuel gas analyzer (27).

[0017] Figure 2 The Rayleigh scattering combustion field gas temperature measurement flow chart based on gas sampling analysis.

[0018] Figure 3 The Rayleigh scattering signal and fluctuation value at room temperature.

[0019] Figure 4 The room temperature and flame measurement signal value at the same power.

[0020] Figure 5 The position temperature distribution diagram with the furnace head as the center origin. (Five) Specific embodiments

[0021] The application will be further described below in combination with examples.

[0022] The structure of the application is as follows Figure 1As shown, the continuous laser emitted by the laser (1) is modulated into intermittent pulse signal by the optical chopper (2), and the beam is lightened by the diaphragm (3), and the linearly polarized light is divided into P-polarized light propagating along the incident light direction and S-polarized light perpendicular to the incident direction by the combination of the half-wave plate (4) and the high-power laser polarization beam splitter prism (5), the P-polarized light passes through the inside of the darkroom (6), and the displacement table (7) and the macken burner (8) above the power meter probe (10) rake surface, the required Rayleigh scattering light is received by the photomultiplier tube (14) through the convergence of the convex lens (12) and the filtering of the optical filter (13), and the signal collected by the data acquisition system (15) is transmitted to the host computer (16) after sampling, and the Rayleigh scattering signal processing is realized on the host computer (16); the four-wire platinum resistance (17) and the digital multimeter (18) are combined to realize the measurement of the initial room temperature; the air pump (22), the gate valve (23), the flow meter (24) and the flow control system (25) are combined to realize the flow control of the air (19), the propane (20) and the nitrogen (21); the gas sampling bottle (26) and the gas analyzer (27) are combined to realize the analysis of the concentration of each substance in the flame; the specific process flow chart of measuring the flame temperature based on Rayleigh scattering is as shown in Figure 2 As shown, the process includes the following steps:

[0023] Step one: this example takes propane equivalent ratio equal to 1 as an example, for hydrocarbon fuel CxHy, the stoichiometric relationship is as follows:

[0024] CxHy+a(O2+3.76N2)→xCO2+(y / 2)H2O+3.76aN2 (5)

[0025] Wherein a=x+y / 4, the equivalent ratio of CxHy:Air(O2, N2) is 1:a, the air flow is set to 30L / min in the experiment, and the propane flow is 1.26L / min according to the equivalent ratio of 1. At the beginning of the experiment, start the digital multimeter (18), place the four-wire platinum resistance (17) above the burner head, read the resistance value of the platinum resistance after the reading is stable, and record the temperature at this time as T1=26.47℃ according to the Pt100 scale; turn on the preheated laser (1) and optical chopper (2), the scattering light at room temperature is filtered by the optical filter (13) and converged by the convex lens (12), and finally received by the photomultiplier tube (14), the signal collected by the data acquisition system (15) is read in real time by the host computer (16), and the signal processing is carried out after the signal value is stable for a period of time, and the Rayleigh scattering signal S(T1) at room temperature is obtained. -03 V.

[0026] Step two: open the air pump (22), gate valve (23), flow meter (24), flow control system (25), set the air (19) flow rate to 30L / min, the flow rate of propane to 1.26L / min, the flow rate of nitrogen to 10L / min through the flow control (25), ignite, move the McKenna burner (7) on the displacement table (8) to the left end to the center position of the signal receiving device by operating the displacement table controller (9), the surface of the burner is 20mm away from the laser light path, observe the Rayleigh scattering signal of the flame area in real time through the upper computer (16), process the signal after the scattering signal is stable, and obtain the flame Rayleigh scattering signal S(T2) = 3.77309*e -04 ; connect the gas sampling bottle (26) to the sampling point through the sampling valve, open the sampling valve for sampling, analyze the sample using the gas analyzer (27), record the concentration of each substance, and calculate the Rayleigh differential scattering cross section at this time, and divide the Rayleigh differential scattering cross section of air to obtain the Rayleigh differential scattering cross section ratio The flame temperature is calculated by the formula = 1756K, and the iteration is performed until convergence; move the displacement table to the left by 2mm, repeat the above steps, and stop until the photomultiplier tube no longer receives the Rayleigh scattering signal of the flame area; move the displacement table down by 10mm, repeat the above steps, and the flame temperature field distribution at a height of 30mm is obtained; move the displacement table (7) in turn, and the flame temperature measurement of the required area is completed.

[0027] The above description of the present application and its embodiments is not limited to this, and the drawings shown are only one of the embodiments of the present application. Without departing from the purpose of the present application, similar structures or examples can be designed without creativity, which are all within the protection scope of the present application.

Claims

1. A method for measuring the temperature of a Rayleigh scattering combustion field gas based on gas sampling and analysis. This method is based on a Rayleigh scattering combustion field gas temperature measurement system, which comprises a laser source, an optical chopper, an aperture, a half-wave plate, a high-power laser polarization beam splitter, a darkroom, a displacement stage, a McKenna burner, a power meter and probe, a convex lens, a filter, a photomultiplier tube, a data acquisition system, a host computer, a four-wire platinum resistance thermometer, a digital multimeter, a flow meter, a flow control system, a gas sampling bottle, and a gas analyzer. The laser continuously emits laser light, which is modulated into intermittent pulse signals by the optical chopper. The light is then locked by the aperture and a sleeve, and subsequently, the laser light passes through the half-wave plate and interacts with the high-power laser... A beam-splitting prism splits light into P-polarized and S-polarized beams, which then enter the dark chamber through a coaxial optical path and reach the flame region of the McKenna combustion furnace. The Rayleigh scattering signal of the standard flame is converged to the receiving device—a photomultiplier tube—by a convex lens imaging system. A 532nm filter in front of the photomultiplier tube filters out non-Rayleigh scattering signals. The received signal is uploaded to a host computer through an acquisition system. The host computer demodulates the signal and outputs the optical signal value within the flame temperature field. A gas analyzer is used to obtain the component concentrations of each substance within the flame temperature field. By consulting literature and calculations, the Rayleigh scattering cross section of the flame at different concentrations of each substance is obtained. The flame temperature value is then obtained through formula calculation and iteration.

2. The Rayleigh scattering combustion field gas temperature measurement method based on gas sampling analysis according to claim 1, characterized in that, Room temperature was measured using a platinum resistance thermometer. Rayleigh scattering thermometry was calibrated with the platinum resistance thermometer in ambient air before measurement, ensuring that the non-contact temperature measurement results were directly traceable to the basic definition of the ITS-90 temperature standard. A stable, controllable, and reproducible flame was constructed using a McKenna standard flame deflector, and the component concentrations of various substances in the combustion field were obtained through gas sampling and analysis. First, the room temperature value T1 obtained from the platinum resistance thermometer measurement was recorded. Then, the laser was activated, and the Rayleigh scattering light signal measured at room temperature was recorded as S(T1), while the Rayleigh scattering light signal measured in the standard flame field was recorded as S(T2). Where η is the optical detection efficiency, I is the incident laser intensity, N1 is the particle number density of air, N2 is the particle number density of species in the flame, and V is the scattering volume. It is the differential scattering cross section of air. The flame differential scattering cross section is ΔΩ, which is the optical collection solid angle. Equations (1) and (2) can be simplified by the ideal gas law formula (3) to obtain the relationship between temperature and Rayleigh scattered light signal: Where k is Boltzmann constant, the room temperature T1, the Rayleigh scattering light signal S(T1) at room temperature, and the Rayleigh scattering light signal S(T2) in the standard flame field have been obtained through measurement. The value of the Rayleigh differential scattering cross section of the gas is determined by equation (5). When calculating the Rayleigh differential scattering cross section of the flame in equation (5), it is necessary to know the component concentration of each substance in the flame. The component concentration of the sample point is obtained by gas analysis. The gas sampling bottle is connected to the sampling point through the sampling valve. The sampling valve is opened to take a sample. The gas analyzer is used to analyze the substance concentration of the sample and record the concentration of each substance. The Rayleigh differential scattering cross section value of each substance in equation (5) is calculated by equation (6). The calculated value is substituted into equation (5) to obtain the Rayleigh differential scattering cross section value of the gas. At this time, the values ​​of each parameter in equation (4) are known. The flame temperature T2 is obtained by substituting them. Among them, X i It is the mole fraction of the i-th species. Substitute the flame temperature T2 obtained from equations (5) and (6) into equation (7) for iteration, and repeat the above steps until convergence.

3. The Rayleigh scattering combustion field gas temperature measurement method based on gas sampling analysis according to claim 1, characterized in that, The aperture, half-wave plate, and high-power laser polarization beam splitter in the system are coaxial with the laser optical path, and the optical axis of the photomultiplier tube is orthogonal to the laser optical path and located on the same horizontal plane as the laser optical path.

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