Rayleigh scattering combustion field gas temperature measuring method and system based on gas sampling analysis

Abstract

The invention provides a Rayleigh scattering combustion field gas temperature measuring method and system based on gas sampling analysis, belongs to the technical field of optical measurement, and is used for measuring the gas temperature of a standard flame combustion field. Compared with a traditional contact type flame temperature measuring method, the Rayleigh scattering method does not influence flame characteristics and has high precision and high resolution, and the existing Rayleigh scattering flame temperature measuring method generally needs simulation software to obtain the component concentration of each substance in a combustion field. However, there is a certain deviation between the data obtained through simulation and the actual situation. The component concentration of each substance in the combustion field is acquired by adopting a gas sampling method, so that the acquisition of the concentration of each substance in the combustion field does not depend on simulation software any more, and during 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 into a gas analyzer for component concentration analysis of each substance. In addition, the technology is calibrated by a platinum resistor in a normal-temperature air environment before measurement, so that the non-contact temperature measurement result is directly traced back to the temperature standard ITS-90. The method and the system realize complete measurement of the gas temperature of the combustion field, and have a wide application prospect in the aspect of standard flame measurement.

Description

(I) Technical field

[0001] The present invention proposes a method and system for measuring the gas temperature of a combustion field based on Rayleigh scattering of gas sampling analysis, which belongs to the field of optical measurement technology. The method and system combine gas sampling analysis with Rayleigh scattering, eliminate the uncertainty and error caused by the simulation analysis of the gas concentration in the combustion field, and realize the complete measurement of the gas temperature in the combustion field. At the same time, the room temperature is measured by platinum resistance. Before the measurement, the Rayleigh scattering temperature measurement in the normal temperature air environment is calibrated by the platinum resistance, so that the non-contact temperature measurement result can be directly traced back to the temperature standard ITS-90. (II) Background technology

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

[0003] The traditional contact measurement of flame temperature requires direct contact with 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 requires simulation software to obtain the component concentration of each substance in the combustion field. The data obtained by simulation has a certain deviation from the actual situation. The present invention adopts a method combining gas sampling analysis with Rayleigh scattering temperature measurement to obtain the component concentration of each substance in the combustion field, so that the acquisition of the concentration of each substance in the combustion field is no longer dependent on simulation software, and the room temperature is measured using a calibrated platinum resistor. Subsequently, the room temperature in the same environment is measured using Rayleigh scattering technology, and the scattered light signal is recorded. Through multiple comparative measurements, the relationship between the Rayleigh scattering measurement temperature system and the standard temperature is established, thereby realizing the traceability of the temperature standard ITS-90. (III) Summary of the invention

[0004] In view of the problems of low spatial resolution of traditional flame measurement methods, which will affect the flow field and temperature distribution of the flame, the present invention proposes a method and system for measuring temperature based on Rayleigh scattering. The gas sampling method is adopted to obtain the component concentration of each substance in the flame, so that the acquisition of the concentration of each substance component in the process of Rayleigh scattering temperature measurement no longer depends on simulation software such as Gaseq, and platinum resistance calibration is used to realize the traceability of ITS-90.

[0005] The system consists of a laser light source, a chopper, an aperture, a sleeve, a half-wave plate, a high-power laser polarization beam splitter, a darkroom, a McKenna burner, a translation stage, a power meter and a probe, a convex lens, a filter, a photomultiplier tube, an acquisition system, a host computer, a digital multimeter, a four-wire platinum resistor, a gas sampling bottle, and a gas analyzer. The laser continuously emits laser light, which is modulated into an intermittent pulse signal by an optical chopper, and is locked by an aperture, a sleeve, and other devices. The laser light is then divided into P-polarized light and S-polarized light by a half-wave plate and a high-power laser polarization beam splitter, and then enters the darkroom through a coaxial optical path. Arriving at the flame area of ​​the McKenna burner, the Rayleigh scattering signal of the McKenna burner flame is converged to the receiving device - the photomultiplier tube through the convex lens imaging system. There is a 532nm filter in front of the photomultiplier tube to filter the non-Rayleigh scattering signal. The received signal is uploaded to the host computer through the acquisition system; the signal is demodulated in the host computer, and the light signal value in the flame temperature field is output. The gas analyzer is used to obtain the component concentration of each substance in the flame temperature field. The flame Rayleigh scattering cross section at different concentrations of each substance is obtained by consulting the data and calculation, and the flame temperature value is obtained by formula calculation and iteration. During the whole process, the power meter is used to monitor the laser power. The specific measurement steps are as follows:

[0006] Step 1: A method and system for measuring the gas temperature of a combustion field based on Rayleigh scattering gas sampling analysis according to claim 1, characterized in that the room temperature is measured by a platinum resistor, and the Rayleigh scattering temperature measurement in a room temperature air environment is calibrated by the platinum resistor before the measurement, so that the non-contact temperature measurement result can be directly traced back to the basic definition of the temperature standard ITS-90; first, the laser is started for preheating, and the room temperature of the experimental area is measured with a calibrated four-wire platinum resistor, and the resistance value of the platinum resistor is read by a digital multimeter, and the read resistance value is compared with the Pt100 graduation table, and the room temperature T1 at the beginning of the experiment is recorded; after the preheating is completed, the laser is turned on, the laser emits a continuous laser, and the continuous laser is modulated into an intermittent pulse signal by an optical chopper, and the modulated laser is constrained by a sleeve, an aperture and other devices to constrain the beam diameter, and at the same time, unnecessary stray light in the optical system is shielded to improve the signal-to-noise ratio; then the laser passes through a semi-circular Wave plate and high-power laser polarization beam splitter. The half-wave plate introduces phase delay to linear polarized light to change the polarization direction of light. The polarization beam splitter divides the light beam into P polarized light and S polarized light according to the polarization state of light. P polarized light is transmitted, while 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, thereby increasing the intensity of the Rayleigh scattered light finally received by the receiving device. Subsequently, the scattered light of the laser is converged onto the 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, leaving only 532nm Rayleigh scattered light, ensuring the accuracy of temperature measurement. 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 shines on the rake surface of the power meter probe. The power meter monitors the real-time power of the laser and observes the stability of the laser.

[0009] Step 2: A method and system for measuring gas temperature in a Rayleigh scattering combustion field based on gas sampling and analysis as described in claim 1, characterized in that a real-time analysis of the concentration of each substance in the flame is achieved through a gas sampling bottle and a gas analyzer, eliminating the situation where the substance concentration obtained by simulation software such as Gaseq is inconsistent with the actual situation, making the temperature calculation process more convincing; first open the nitrogen valve, and after passing nitrogen for a period of time, open the propane and air cylinders, and control the flow of the two gases through a flow control system to achieve a specific equivalent ratio. After the gas valve is opened, ignite, and move the displacement stage until the center plane of the photomultiplier tube is flush with the leftmost end of the furnace head, and the furnace head surface is 20mm away from the laser. The signal acquisition work of the sampling point is realized by the acquisition system and the host computer, and the flame light signal collected at this time is recorded as S(T2):

[0010]

[0011] After simplifying the ideal gas law formula, the relationship between temperature and signal is 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 into the sampling bottle smoothly, and exhaust the sampling bottle before sampling to ensure that the air or residual gas inside the sampling bottle is removed. After sampling, connect the sampling bottle to the sampling analyzer to obtain the component concentration of each substance at the sampling point, and then you can get the Rayleigh scattering cross section of the flame:

[0014]

[0015] X i is the component concentration of each substance, is the Rayleigh scattering cross section of the flame. Substituting the above value into formula (3) can obtain the flame temperature at the sampling point. After the signal acquisition is completed, move the translation stage 2mm to the left and repeat the above steps until the photomultiplier tube can no longer receive the Rayleigh scattering signal in the flame field. At this time, the flame temperature distribution on the horizontal plane 20mm above the furnace head is obtained. (IV) Description of the drawings

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

[0017] Figure 2 It is a flow chart of the gas temperature measurement in Rayleigh scattering combustion field based on gas sampling analysis.

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

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

[0020] Figure 5 It is a flame position temperature distribution diagram with the center point of the burner as the origin. (V) Specific implementation methods

[0021] The present invention will be further described below in conjunction with examples.

[0022] The structure of the present invention is as follows Figure 1As shown, the continuous laser emitted by the laser (1) is modulated into an intermittent pulse signal by an optical chopper (2), and the light is focused by an aperture (3). The linearly polarized light is divided into P polarized light propagating along the direction of the incident light and S polarized light perpendicular to the incident direction by a combination of a half-wave plate (4) and a high-power laser polarization beam splitter (5). The P polarized light passes through the inside of a darkroom (6), a translation stage (7), and the McKenna combustion furnace (8) and is incident on the rake surface of a power meter probe (10). The required Rayleigh scattered light is collected by a convex lens (12) and filtered by a filter (13) and is received by a photomultiplier tube (14). The data acquisition system (15) samples and transmits the data to the host computer (16), and the host computer (16) processes the Rayleigh scattering signal. The four-wire platinum resistor (17) is combined with the digital multimeter (18) to measure 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 control the flow of air (19), propane (20), and nitrogen (21). The gas sampling bottle (26) is combined with the gas analyzer (27) to analyze the concentration of each substance in the flame. The specific process flow chart of measuring flame temperature based on Rayleigh scattering is as follows: Figure 2 As shown, the following steps are included:

[0023] Step 1: This example takes the 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] Where a=x+y / 4, the chemical equilibrium equivalent ratio CxHy:Air(O2,N2)=1:a, the air flow rate in the experiment is set to 30L / min, and based on the equivalent ratio of 1, the propane flow rate can be obtained to be 1.26L / min. At the beginning of the experiment, the digital multimeter (18) is started, and the four-wire platinum resistor (17) is placed above the furnace head. After the reading is stable, the resistance value of the platinum resistor is read as 110.305Ω. The resistance value is compared with the Pt100 scale, and the temperature at this time is recorded as T1=26.47°C; the preheated laser (1) and optical chopper (2) are turned on, and the scattered light at room temperature is filtered by the filter (13) and converged by the convex lens (12), and finally received by the photomultiplier tube (14). The signal collected by the acquisition system 15 is read in real time by the host computer (16), and the signal value is stabilized for a period of time before the signal is processed to obtain the Rayleigh scattering signal S(T1)=1.904*e at room temperature. -03 V.

[0026] Step 2: Turn on the air pump (22), the gate valve (23), the flow meter (24), and the flow control system (25). Set the flow rate of air (19) to 30 L / min, the flow rate of propane to 1.26 L / min, and the flow rate of nitrogen to 10 L / min through the flow control (25). Ignite. Move the leftmost end of the McKenna burner (7) on the translation stage (8) to the center of the signal receiving device by operating the translation stage controller (9). The surface of the burner head is 20 mm away from the laser optical path. Observe the Rayleigh scattering signal of the flame area in real time through the host computer (16). After the scattering signal is stable, process the signal to obtain the flame Rayleigh scattering signal S(T2)=3.77309*e at the sampling point. -04 Connect the gas sampling bottle (26) to the sampling point through the sampling valve, open the sampling valve to take samples, use the gas analyzer (27) to analyze the substance concentration of the sample, record the concentration of each substance, and calculate the Rayleigh differential scattering cross section of the gas at this time, and divide it by the Rayleigh differential scattering cross section of the air to obtain the Rayleigh differential scattering cross section ratio The flame temperature is calculated by the formula =1756K, and iterate until convergence; move the translation stage to the left by 2mm, and repeat the above steps until the photomultiplier tube no longer receives the Rayleigh scattering signal in the flame area; move the translation stage downward by 10mm, and repeat the above steps to obtain the flame temperature field distribution at a height of 30mm. Move the translation stage (7) in sequence to complete the flame temperature measurement of the required area.

[0027] The above description of the present invention and its embodiments is not limited thereto, and the accompanying drawings are only one embodiment of the present invention. Without departing from the purpose of the present invention, any structure or embodiment similar to the technical solution designed without creativity shall fall within the protection scope of the present invention.

Claims

1. A method and system for measuring the temperature of a gas in a combustion field of Rayleigh scattering based on gas sampling and analysis, the system comprising a laser light source, an optical chopper, an aperture, a half-wave plate, a high-power laser polarization beam splitter, a darkroom, a translation stage, a McKenna burner, a power meter and a probe, a convex lens, a filter, a photomultiplier tube, an acquisition system, a host computer, a four-wire platinum resistor, 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 an intermittent pulse signal by an optical chopper, and is locked by an aperture, a sleeve, and the like, and then the laser light is separated into a P polarization beam splitter by a half-wave plate and a high-power laser polarization beam splitter. The S-polarized light and the S-polarized light enter the darkroom through the coaxial optical path and reach the flame area of ​​the McKenna combustion furnace. The Rayleigh scattering signal of the standard flame is converged to the receiving device - the photomultiplier tube through the convex lens imaging system. There is a 532nm filter in front of the photomultiplier tube to filter the non-Rayleigh scattering signal. The received signal is uploaded to the host computer through the acquisition system; the signal is demodulated in the host computer, and the light signal value in the flame temperature field is output. The component concentration of each substance in the flame temperature field is obtained by using the gas analyzer. The flame Rayleigh scattering cross section at different concentrations of each substance is obtained by consulting the data and calculation, and the flame temperature value is obtained by formula calculation and iteration.

2. A method and system for measuring gas temperature in a Rayleigh scattering combustion field based on gas sampling analysis according to claim 1, characterized in that: The room temperature is measured by platinum resistance. The Rayleigh scattering temperature measurement in the room temperature air environment is calibrated by the platinum resistance before measurement, so that the non-contact temperature measurement result can be directly traced back to the basic definition of the temperature standard ITS-90. The McKenna standard flat flame device is used to build a stable, controllable and reproducible flame, and the component concentration of each substance in the combustion field is obtained through gas sampling and analysis. First, the room temperature value T1 measured by the platinum resistance is recorded, and the laser is started. The Rayleigh scattering light signal measured at room temperature is recorded as S(T1), and the Rayleigh scattering light signal measured in the standard flame field is recorded as S(T2). According to the ideal gas law formula (3), equations (1) and (2) can be simplified to obtain the relationship between temperature and Rayleigh scattered light signal: In the above formula, the room temperature T1, the Rayleigh scattered light signal S(T1) at room temperature, and the Rayleigh scattered light signal S(T2) in the standard flame field have been obtained through measurement, wherein the value of the Rayleigh differential scattering cross section of the fuel gas is determined by formula (5). When calculating the Rayleigh differential scattering cross section of the flame in formula (5), it is necessary to know the component concentration of each substance in the flame. For obtaining the concentration of each substance component in the flame, simulation software is generally used to obtain the concentration. In the present invention, a fuel gas analysis method is used to obtain the substance component concentration at the sampling point, a fuel gas sampling bottle is connected to the sampling point through a sampling valve, the sampling valve is opened for sampling, and the substance concentration of the sample is analyzed by a fuel gas analyzer, and the concentration of each substance is recorded respectively. The Rayleigh differential scattering cross section value of each substance in formula (5) is calculated by formula (6). The calculated value is substituted into formula (5) to obtain the Rayleigh differential scattering cross section value of the fuel gas. At this time, the values ​​of each parameter in formula (4) are known, and the flame temperature T2 is obtained by substitution. Substitute the flame temperature T2 obtained into equation (7) and iterate, repeating the above steps until convergence.

3. A method and system for measuring gas temperature in a Rayleigh scattering combustion field based on gas sampling analysis according to claim 1, characterized in that: The optical elements in the system are all coaxial with the laser optical path, wherein the signal receiving device is orthogonal to the laser optical path and is located on the same horizontal plane as the laser optical path.

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