CN115855301A - Laser spectrum temperature measuring device and method based on quartz tuning fork detection - Google Patents
Laser spectrum temperature measuring device and method based on quartz tuning fork detection Download PDFInfo
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Abstract
The invention discloses a laser spectrum temperature measuring device and method based on quartz tuning fork detection, wherein the device comprises a semiconductor laser, a laser alignment system, a combustion field, a quartz tuning fork, a control and data acquisition processing system and a computer which are sequentially arranged along a light beam propagation direction, the semiconductor laser modulated by the control and data acquisition processing system outputs laser, the laser passes through the laser alignment system and then is incident to pass through the combustion field, CO gas in the combustion field absorbs part of laser energy and then irradiates the root of the quartz tuning fork, the quartz tuning fork generates an electric signal, the electric signal is input into the control and data acquisition processing system to demodulate and acquire the signal, the control and data acquisition processing system is connected with the computer, and temperature inversion and display are carried out in the computer. The invention solves the problem that the wavelength response of the photoelectric detector in the temperature measuring device is limited when CO is used as the detection gas in the conventional combustion field temperature measurement.
Description
Technical Field
The invention relates to a laser spectrum temperature measuring device and method, in particular to a laser spectrum temperature measuring device and method based on quartz tuning fork detection.
Background
The combustion flow field process is complex and severe, and the real-time diagnosis of the instantaneous environment is extremely strict. The optical diagnosis technology of the combustion flow field mainly takes a laser technology, a spectrum technology, a photoelectric detection technology and the like as detection principles, and realizes high-spatial-temporal-resolution accurate measurement of parameters such as the temperature, the components, the concentration, the flame structure, the flow velocity and the like of the combustion flow field. The temperature is an extremely important physical quantity in a combustion flow field, and the measurement of the temperature has important significance on combustion dynamics, engine combustion efficiency, pollution control and the like.
In recent years, laser-based spectral diagnostic techniques are becoming the mainstream of combustion tests as alternatives to traditional thermometry. Among them, tunable Diode Laser Absorption Spectroscopy (TDLAS) is the most commonly used method for on-line monitoring of temperature and components in a combustion field. The TDLAS technology measurement principle is based on Beer-Lambert law, a semiconductor laser with rapidly tunable wavelength is adopted to generate single longitudinal mode laser, and a detector is used for measuring the change condition of light intensity before and after the medium absorbs the laser.
The TDLAS measurement flow field temperature principle is as follows: the distribution of the distribution numbers on different energy levels of the molecules is related to the temperature (the Boltzmann statistical distribution is satisfied), the absorption intensity of the absorption lines is related to the population number of the corresponding energy level, and the temperature of the combustion field can be obtained by measuring the relative intensity of the different absorption lines. The specific implementation method comprises the following steps: two absorption lines with different dependence relations of line intensity on temperature are selected, the flow field temperature is inverted through a single-value function of the ratio of the two absorption lines to the temperature, two absorption lines are scanned by two diode lasers simultaneously, or two adjacent absorption lines are scanned by a single diode laser. Ln (I) for the absorbed intensity and the baseline intensity 0 The operation of/I) can obtain two absorption peak curves, and for the wavelength scanning direct absorption method, the ratio of the areas of the two absorption peaks is equivalent to the ratio of the line intensities of the two absorption lines.
According to beer-lambert law:
ln(I 0 /I)＝PXS(T)φ(ν)L (1)
in the formula I 0 Is the intensity of the incident laser light; i is the intensity of the emergent laser; p is the total pressure of the detection gas; x is the mole fraction of the probe component; s (T) is the spectral line intensity of the absorption spectral line; t is the temperature of the test environment;
is a linear function; v is the frequency of the laser; and L is the effective propagation distance of the laser in the absorption medium.
In the wavelength scanning modulation absorption method, sine wave is superposed on sawtooth wave to modulate the wavelength of laser, and the bilinear method, i.e. the height S of second harmonic signal of two absorption spectral lines is used 1 、S 2 (value at center frequency) ratio, and setting the center frequencies of the two absorption spectral lines as v 1 V and v 2 Then:
in the formula, R 2f Is the ratio of the second harmonic signal intensity; a is the wavelength modulation depth. Temperature measurement by wavelength modulation absorption method except for second harmonic signal intensity R under two absorption 2f Besides, the method is also related to the wavelength modulation depth a, the laser intensity I and the linear function phi, and the flow field temperature inversion formula of the wavelength modulation absorption second harmonic method is as follows:
in the formula, E' is the lower energy level energy of an absorption spectral line; h is the Planck constant; c is the speed of light; k is Boltzmann constant; t is 0 Is the reference temperature. In the existing experimental scheme, the TDLAS temperature measurement system mainly comprises a light source, a modulator, a combustion field, a photoelectric detector and other equipment. Output laser of tunable semiconductor laser is collimatedAnd exciting the gas to be detected in the combustion field, absorbing partial energy of laser by the gas, and irradiating the light sensitive surface of the photoelectric detector with the emergent laser for detecting the change of light intensity.
Water is a ubiquitous component of hydrocarbon fuel combustion fields, and has a strong oscillation energy level absorption band in visible to mid-infrared bands. In a combustion field temperature measurement experiment, water is generally used for combustion field measurement, but water vapor in air can influence the experiment measurement to reduce the temperature measurement accuracy, so that CO and CO with lower content in air can be adopted 2 And carbon oxides generated by combustion are used as detection targets. Adopt photoelectric detector as light intensity detection component in traditional TDLAS temperature measurement experiment, and photoelectric detector has wavelength response restriction, at CO, CO 2 Photoelectric detectors at the response part of the middle infrared band spectral line are rare and expensive, so that the experiment cost is high, and in addition, compared with near infrared band elements, the performances of the photoelectric detectors are general, and the temperature measurement performance is influenced.
Disclosure of Invention
In order to solve the problem that the wavelength response of a photoelectric detector in a temperature measuring device is limited when CO is used as detection gas in the conventional combustion field temperature measurement, the invention provides a laser spectrum temperature measuring device and method based on quartz tuning fork detection by utilizing the principle of a wavelength modulation absorption method.
The purpose of the invention is realized by the following technical scheme:
a laser spectrum temperature measuring device based on quartz tuning fork detection comprises a semiconductor laser, a laser alignment system, a combustion field, a quartz tuning fork, a control and data acquisition processing system and a computer which are sequentially arranged along a light beam propagation direction, wherein the semiconductor laser modulated by the control and data acquisition processing system outputs laser, the laser passes through the laser alignment system and then enters the combustion field, CO gas in the combustion field absorbs part of laser energy and then irradiates the root of the quartz tuning fork, the quartz tuning fork generates an electric signal, the electric signal is input into the control and data acquisition processing system to demodulate and acquire the signal, the control and data acquisition processing system is connected with the computer, and temperature inversion and display are carried out in the computer.
A method for measuring the temperature of the laser spectrum by using the device comprises the following steps:
the method comprises the following steps: selecting CO as a detection gas target, controlling the output characteristic of the semiconductor laser by using a control and data acquisition processing system by using a wavelength modulation absorption method, scanning the output wavelength of the semiconductor laser in a sawtooth wave form, superposing a sine wave on the sawtooth wave for modulation, and controlling a scanning range to completely cover two continuous absorption lines of the CO;
step two: laser output by the semiconductor laser is emitted into a combustion field after passing through a laser collimation system to excite CO of target gas to be detected, CO gas medium absorbs the laser, the light intensity of the laser generates periodic variation, the quartz tuning fork is excited to generate periodic elastic deformation when the laser irradiates the root of the quartz tuning fork, and the quartz tuning fork generates resonant oscillation under the action of the laser to generate a current signal;
step three: the quartz tuning fork is accessed to the control and data acquisition processing system to demodulate and acquire signals, and the signals are input into a computer to perform temperature inversion processing.
In the temperature detection technology based on the quartz tuning fork, CO is selected as a detection gas target, the output wavelength of the semiconductor laser is scanned in a sawtooth wave form by using a wavelength modulation absorption method, the scanning range completely covers two continuous absorption lines of the CO, a sine wave with higher frequency is superposed on the sawtooth wave for modulation, and when the laser wavelength scans an absorption line, because the line shape of the medium absorption line is a Voigt function, the frequency of the change of the laser light intensity after passing through the absorption medium also comprises harmonic components besides the modulation frequency. The wavelength modulation method generally measures the parameters of the flow field by measuring the second harmonic signal of the modulated signal after the laser passes through the absorption medium.
The laser output by the tunable semiconductor laser is collimated and passes through a combustion field and irradiates the root of the quartz tuning fork, CO gas medium in the combustion field absorbs the laser, the light intensity of the laser can generate periodic variation due to medium absorption, and the laser is excited due to the photo-induced thermal elastic effect when irradiating the root of the quartz tuning forkThe quartz tuning fork is excited to generate periodic elastic deformation, namely the quartz tuning fork generates resonance oscillation under the action of laser, and the oscillation generates a current signal based on the piezoelectric effect of the quartz tuning fork. Demodulating two second harmonic signals S by using a phase-locked amplifier unit included in a control and data acquisition processing system 1 And S 2 The temperature of the combustion field can be obtained by substituting the ratio of the two second harmonic peaks into equation (4).
Compared with the prior art, the invention has the following advantages:
1. the quartz tuning fork with wide spectral response range, high sensitivity and low cost is selected as the detection unit of the light intensity variation, so that the problems of limited coverage range and high price of the traditional mid-infrared detection waveband detector are solved;
2. the quartz tuning fork has the advantage of high quality factor Q >10000, the detection bandwidth (a few hertz or even lower) of the quartz tuning fork is narrower than that of an optical infrared detector by several orders of magnitude, and the quartz tuning fork can effectively isolate interference and environmental noise caused by other spectrums in a combustion field.
Drawings
FIG. 1 is a schematic structural diagram of a laser spectrum temperature measuring device based on quartz tuning fork detection;
FIG. 2 is a diagram of an experimental setup of a laser spectroscopy temperature measurement device based on quartz tuning fork detection;
FIG. 3 is a second harmonic signal measured in a flat flame burner environment.
Detailed Description
The technical solution of the present invention is further described below with reference to the accompanying drawings, but not limited thereto, and any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be covered by the protection scope of the present invention.
The invention provides a temperature detection method and device based on quartz tuning fork detection by utilizing the principle of a wavelength modulation absorption method, aiming at solving the problem that a photoelectric detector in a temperature measurement device has wavelength response limitation when CO is used as detection gas in the conventional combustion field temperature measurement. The design adopts quartz tuning fork to replace a photoelectric detectorAs a light intensity detection element, a semiconductor laser emits laser, collimated laser passes through a combustion field and then irradiates the root of a quartz tuning fork, laser wavelength scanning comprises two CO absorption lines, when the modulation frequency of the laser is the resonance frequency of the quartz tuning fork, the light intensity excitation causes the resonance of the quartz tuning fork to be enhanced, a mechanical vibration signal is converted into an electric signal through the piezoelectric effect of the quartz tuning fork, a harmonic signal of the electric signal is demodulated through a phase-locked amplifier unit in a control and data acquisition and processing system, and finally signal processing is carried out to obtain a second harmonic signal S 1 And S 2 The combustion field temperature is obtained by substituting the formula (6).
As shown in fig. 1 and fig. 2, the device includes a semiconductor laser 1, a laser alignment system 2, a combustion field 3, a quartz tuning fork 4, a control and data acquisition processing system 5, and a computer 6, which are sequentially arranged along a beam propagation direction, the semiconductor laser 1 modulated by the control and data acquisition processing system 5 outputs laser, the laser passes through the laser alignment system 2 and then enters the combustion field 3, CO gas in the combustion field 3 absorbs a part of laser energy and then irradiates the root of the quartz tuning fork 4, due to a thermoelastic effect and a piezoelectric effect, the quartz tuning fork 4 generates an electrical signal, the electrical signal is input into the control and data acquisition processing system 5 to demodulate and acquire the signal, the control and data acquisition processing system 5 is connected with the computer 6, and temperature inversion and display are performed in the computer 6, and the specific implementation process is as follows:
the method comprises the following steps: the control and data acquisition processing system 5 controls the output characteristics (power, wavelength, modulation rate, etc.) of the semiconductor laser 1;
step two: laser output by the semiconductor laser 1 passes through the laser collimation system 2 and then enters the combustion field 3 to excite CO of target gas to be detected, and the CO absorbs the laser and then emits the laser to irradiate the root of the quartz tuning fork 4.
Step three: the quartz tuning fork 4 is accessed to the control and data acquisition processing system 5 to demodulate and acquire signals, and the signals are input into the computer 6 to be inverted.
In the invention, the semiconductor laser 1 is a distributed feedback type single longitudinal mode semiconductor laser with near infrared continuous wave output, and the line width should not be more than 10MHz.
In the present invention, the tuning range of the semiconductor laser 1 should be > 0.1nm in order to cover both absorption lines.
In the invention, in order to improve the thermoelastic energy amplitude of the quartz tuning fork 4, the laser power of the semiconductor laser 1 should be more than 10mW.
In the invention, the noise of the system is reduced by adopting a wavelength modulation technology, the control and data acquisition processing system 5 modulates the output wavelength of the semiconductor laser 1, and the modulation frequency of the semiconductor laser 1 is equal to half of the resonance frequency of the quartz tuning fork.
In the invention, the control and data acquisition processing system 5 comprises a phase-locked amplifier, a data acquisition card and a signal generator, and in order to realize the demodulation of high-frequency modulation signals, the demodulation bandwidth of the phase-locked amplifier is more than 10kHz.
In the present invention, in order to increase the temperature measurement speed and temperature resolution, the resonant frequency of the quartz tuning fork 4 should be >10kHz.
In the present invention, in order to reduce the influence of the burning field 3 on the thermal noise of the quartz tuning fork 4, the quartz tuning fork 4 should be at least 5cm away from the burning field 3.
In the invention, in order to ensure the accuracy of temperature measurement of the quartz tuning fork 4, the relative sensitivity of the selected absorption spectrum line pair is greater than 1.
In the present invention, in order to reduce the interference of flame jitter to the laser intensity signal, the wavelength scanning frequency of the semiconductor laser 1 should be >10Hz.
In the present invention, the wavelength modulation depth of the semiconductor laser 1 affects the modulation absorption spectrum, and should be optimized to maximize the signal value.
In the invention, the laser after passing through the combustion field 3 is irradiated on the root of the quartz tuning fork, and the specific position is optimized to maximize the signal value.
In the invention, a computer 6 is connected with a control and data acquisition processing system 5 and carries out real-time control and signal acquisition processing through a serial port instruction.
Example (b):
this example utilizes a Mckenna standard flat flame burner as a test pairThe technical solution of the present invention was verified in the case where the equivalence ratio was 1.0. The result of demodulating the light intensity signal detected by the quartz tuning fork is shown in fig. 3. The secondary signals corresponding to the two absorption lines are respectively S 1 And S 2 . According to the formula (4), the temperature of the area to be measured is 2100K, and the test result is close to the calibration value of the combustor. Thus, the method can be used to make temperature measurements.
Claims (10)
1. The laser spectrum temperature measuring device is characterized by comprising a semiconductor laser, a laser alignment system, a combustion field, a quartz tuning fork, a control and data acquisition processing system and a computer which are sequentially arranged along a light beam propagation direction, wherein the semiconductor laser modulated by the control and data acquisition processing system outputs laser, the laser is incident through the combustion field after passing through the laser alignment system, CO gas in the combustion field absorbs part of laser energy and then irradiates the root of the quartz tuning fork, the quartz tuning fork generates an electric signal, the electric signal is input into the control and data acquisition processing system to demodulate and acquire the signal, the control and data acquisition processing system is connected with the computer, and temperature inversion and display are carried out in the computer.
2. The laser spectrum temperature measuring device based on quartz tuning fork detection according to claim 1, characterized in that the semiconductor laser is a distributed feedback type single longitudinal mode semiconductor laser of near infrared continuous wave output, the line width is not greater than 10MHz.
3. The laser spectroscopy temperature measurement device based on quartz tuning fork detection of claim 1, wherein the tuning range of the semiconductor laser is > 0.1nm.
4. The laser spectroscopy temperature measurement device based on quartz tuning fork detection of claim 1, wherein the laser power of the semiconductor laser is >10 mW.
5. The laser spectrum temperature measuring device based on quartz tuning fork detection of claim 1, wherein the modulation frequency of the semiconductor laser is equal to half of the resonance frequency of the quartz tuning fork, and the resonance frequency of the quartz tuning fork is more than 10kHz.
6. The quartz tuning fork detection-based laser spectroscopy temperature measurement device according to claim 1, wherein the demodulation bandwidth of a phase-locked amplifier in the control and data acquisition and processing system is >10kHz.
7. The laser spectroscopy temperature measuring device based on quartz tuning fork detection of claim 1 or 5, wherein the quartz tuning fork should be at least 5cm away from the burning field.
8. The laser spectroscopy temperature measurement device based on quartz tuning fork detection of claim 1, wherein the wavelength scanning frequency of the semiconductor laser is >10Hz.
9. A method of laser spectroscopic temperature measurement using the device of any of claims 1 to 8, characterized in that the method comprises the steps of:
the method comprises the following steps: selecting CO as a detection gas target, controlling the output characteristic of the semiconductor laser by using a control and data acquisition processing system by using a wavelength modulation absorption method, scanning the output wavelength of the semiconductor laser in a sawtooth wave form, superposing a sine wave on the sawtooth wave for modulation, and controlling a scanning range to completely cover two continuous absorption lines of the CO;
step two: laser output by the semiconductor laser is incident into a combustion field after passing through a laser alignment system to excite CO (carbon monoxide) of target gas to be detected, CO gas medium absorbs the laser, the light intensity of the laser generates periodic variation, the quartz tuning fork is excited to generate periodic elastic deformation when the laser irradiates the root of the quartz tuning fork, and the quartz tuning fork generates resonant oscillation under the action of the laser to generate a current signal;
step three: the quartz tuning fork is accessed to the control and data acquisition processing system to demodulate and acquire signals, and the signals are input into a computer to perform temperature inversion processing.
10. The laser spectrum temperature measurement method according to claim 1, wherein in the third step, the temperature inversion formula is:
in the formula, E' is the lower energy level energy of an absorption spectral line; h is the Planck constant; c is the speed of light;
k is Boltzmann constant; t is a unit of 0 Is a reference temperature; r 2f Is the ratio of the second harmonic signal intensity; i is the intensity of the emergent laser; t is the temperature of the test environment; v is the frequency of the laser; s 1 、S 2 The second harmonic signal height of the two absorption lines.
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