CN114646609A - Correction method based on TDLAS absorption method pressure measurement under high mole fraction - Google Patents
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- 238000010521 absorption reaction Methods 0.000 title claims abstract description 48
- 238000000034 method Methods 0.000 title claims abstract description 35
- 238000009530 blood pressure measurement Methods 0.000 title claims abstract description 23
- 238000012937 correction Methods 0.000 title claims abstract description 22
- 238000000041 tunable diode laser absorption spectroscopy Methods 0.000 title claims abstract description 9
- 238000005259 measurement Methods 0.000 claims abstract description 18
- 238000000862 absorption spectrum Methods 0.000 claims description 18
- 230000007613 environmental effect Effects 0.000 claims description 5
- 230000003595 spectral effect Effects 0.000 claims description 5
- 238000001228 spectrum Methods 0.000 claims description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 238000005516 engineering process Methods 0.000 description 5
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
- 239000004065 semiconductor Substances 0.000 description 3
- 241000282376 Panthera tigris Species 0.000 description 2
- 238000004847 absorption spectroscopy Methods 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 2
- 239000010931 gold Substances 0.000 description 2
- 229910052737 gold Inorganic materials 0.000 description 2
- 238000001285 laser absorption spectroscopy Methods 0.000 description 2
- 241001301450 Crocidium multicaule Species 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
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- 238000001514 detection method Methods 0.000 description 1
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- 238000012986 modification Methods 0.000 description 1
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
- G06F17/10—Complex mathematical operations
Abstract
The invention provides a correcting method for pressure measurement based on a TDLAS absorption method under high mole fraction, which aims to solve the technical problems that when the existing TDLAS direct absorption method is used for measuring the pressure of a flow field, the measurement is carried out under the condition that the mole fraction of gas to be measured is small and is kept unchanged, the influence of dynamic change of the mole fraction of the gas to be measured on the pressure and the line width is neglected, and further, large errors are brought to the pressure measurement of the gas to be measured. The correction method provided by the invention simultaneously considers the influence of the pressure and the mole fraction on the line width measurement, realizes more accurate measurement of the gas parameters by correcting the mole fraction of the pressure measurement result, and is suitable for correcting the pressure and the mole fraction measurement result under the wide working condition.
Description
Technical Field
The invention belongs to the technical field of tunable semiconductor laser absorption spectroscopy (TDLAS), and particularly relates to a correction method for pressure measurement based on a TDLAS absorption method under high mole fraction.
Background
Tdlas (tunable Diode Laser Absorption spectroscopy) technology, which is a tunable semiconductor Laser Absorption spectroscopy technology. The method realizes in-situ online non-contact measurement of physical quantities such as temperature, concentration, pressure and the like of a component to be measured by scanning a characteristic absorption spectral line of a gas molecule to be measured by adopting laser with a very narrow bandwidth. With the maturity of near-infrared and mid-infrared semiconductor laser technologies, the reduction of manufacturing cost and the gradual perfection of a molecular absorption spectrum database in recent years, the TDLAS technology has become an important development direction in the field of non-contact diagnosis of complex physical fields by virtue of the advantages of high measurement accuracy, high sensitivity, strong anti-interference capability, compact structure of a measurement device and the like, and is widely applied to gas parameter measurement.
In the pressure measurement of the TDLAS direct absorption method, pressure inversion is generally performed by a line width of an absorption spectrum. The absorption spectrum line type can be approximated to Lorentz line type, and the line width Deltav can be approximated to Lorentz line type
It can be seen that the absorption spectrum linewidth is affected by both the pressure and the mole fraction of the gas to be measured. At a low molar fraction, the amount of the catalyst is,
the line width is mainly influenced by pressure intensity; at higher mole fractions, the effect of mole fraction on line width needs to be considered.
In practice, the relationship between the line width and the pressure is generally determined by laboratory calibration. However, a fixed mole fraction is often set in the calibration, and the influence of the dynamic change of the mole fraction on the pressure is not considered. Chenxiang et al (Chenxiang, Chenrui peak, Yang Chen light, etc.. air pressure accurate measurement based on TDLAS technology. photoelectron laser 2015, 26 (4): 719 and 723.) and segmentum gold tiger et al (segmentum gold tiger, gold star, Wang Guangyu, etc.. measuring gas pressure based on direct coefficient spectroscopy 2016, 36 (4): 7-11.) all proposed methods for inverting gas pressure by measuring water molecule absorption spectroscopy using TDLAS direct absorption method. Liu Shi Wei et al (Liu Shi Wei, Licatalpi, Liyafei, etc. pressure measurement and compensation for mid-infrared methane detection. photonics, 2018, 47 (2): 0230002.) also propose a method for inverting gas pressure by measuring methane molecular absorption spectrum using TDLAS direct absorption method. The mole fraction of the gas molecules measured in the above documents is small (not higher than 5%), and the mole fraction remains unchanged during the experiment, so that the influence of the mole fraction on the line width is not considered.
However, as previously mentioned, the mole fraction versus pressure correction must be considered in the pressure inversion at high mole fractions. In addition, under a high pressure condition, not only the line width is widened due to the increase of the pressure, but also the absorption baseline is increased, so that the accuracy of area measurement is affected, and therefore, the correction relation of the pressure to the absorption area needs to be considered in the calibration of the pressure.
Disclosure of Invention
The invention provides a correction method based on TDLAS (tunable diode absorption spectroscopy) pressure measurement under high mole fraction, which is used for quantitatively correcting TDLAS pressure measurement results and can be used for realizing more accurate measurement of gas parameters.
In order to achieve the purpose, the invention adopts the technical scheme that:
a correction method for pressure measurement based on TDLAS absorption method under high mole fraction is characterized by comprising the following steps:
step 1), calibrating to obtain a known mole fraction X0Under the condition ofThe calibration relation between the absorption spectrum line width delta ν and the pressure intensity P of the gas to be measured, the calibration relation A ═ G (P) between the absorption area A and the pressure intensity P, and the relation A ═ H (X) between the absorption area A and the mole fraction X of the gas to be measured under normal pressure;
step 2), performing absorption spectrum measurement on the gas to be measured to obtain absorption spectrum data, and obtaining evolution data of the line width delta ν and the absorption area A of the absorption spectrum along with time through spectrum fitting;
step 3), obtaining the environmental pressure P by inversion according to the calibration relation delta v between the line width delta v and the pressure P (F (P)1Time evolution information of;
P1＝F-1(Δν)；
step 4), obtaining the corrected absorption area A by inversion according to the calibration relation A between the absorption area A and the pressure P (G (P)1：
A1＝G(P1)；
Then, by using the calibration relation A between the mole fraction X and the absorption area A, the corresponding mole fraction X is calculated1Time evolution information of (a):
X1＝H-1(A1)＝H-1[G(P1)]；
step 5) Using the known mole fraction X at calibration0And the calculated mole fraction X1To pressure P1Correcting to obtain corrected pressure P2Time evolution information of;
step 6), repeating the steps 4) and 5), and calculating the corrected mole fraction X of different iteration times nn+1Time evolution information and pressure Pn+2Until the pressure data is converged, the obtained pressure is the environmental pressure P of the gas to be measuredn+2；
Wherein n is 0,1,2,3 and is an integer.
Further, the iteratively modified mole fraction Xn+1The time evolution information of (a) is:
Xn+1＝H-1(An+1)＝H-1[G(Pn+1)]
the iteratively corrected pressure Pn+2The time evolution information of (a) is:
wherein n is 0,1,2,3, and r is the aspect ratio of the gas to be measured.
Further, the pressure data converges to a pressure error smaller than a set threshold value after two successive iterative corrections.
Further, the threshold is 1%.
Further, the aspect ratio r is the ratio of the self-broadening coefficient and the air broadening coefficient of the gas to be measured at a specific absorption spectral line, and is obtained by querying a database.
The method can be used for quantitatively correcting the TDLAS pressure measurement result, can realize more accurate measurement of gas parameters, and is suitable for correcting the pressure and mole fraction measurement result under the wide working condition.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the correcting method for pressure measurement based on the TDLAS absorption method under the high mole fraction, the influence of the pressure and the mole fraction on line width measurement is considered, and the gas parameters can be measured more accurately by correcting the mole fraction of the pressure measurement result.
2. The correction method for pressure measurement based on the TDLAS absorption method under the high mole fraction provided by the invention is wide in application range, and iterative correction of the pressure and the mole fraction can be used for correcting the pressure and mole fraction measurement result under the wide working condition.
Drawings
FIG. 1 is a flow chart of the steps of the present invention for a high mole fraction TDLAS absorption based pressure measurement correction method;
FIG. 2 is a typical absorption spectrum of a gas to be measured;
FIG. 3 is a typical time evolution of ambient pressure from line width direct inversion;
FIG. 4 is a typical time evolution of mole fraction information obtained by direct inversion of the corrected absorption area;
FIG. 5 is a diagram illustrating pressure time evolution information obtained after iterative correction for different times;
fig. 6 shows the mole fraction time evolution information obtained after different times of iterative corrections.
Detailed Description
To make the objects, advantages and features of the present invention more apparent, a method for correcting pressure measurement based on TDLAS absorption method at high mole fraction according to the present invention is further described in detail with reference to the accompanying drawings and specific examples.
As shown in fig. 1, the method for correcting pressure measurement based on TDLAS absorption method at high mole fraction in this embodiment includes the following steps:
step 1), obtaining the known mole fraction X at normal temperature through experimental calibration0Under the condition, the calibration relation between the line width Deltav of a certain absorption spectrum of water in the air and the pressure P, the calibration relation A & G & P between the absorption area A and the pressure P, and the relation A & H & X between the absorption area A and the mole fraction X of the water in the air at normal temperature and normal pressure.
And 2) igniting a certain combustion chamber, and carrying out absorption spectrum measurement on water molecules in the combustion chamber, as shown in FIG. 2, so as to obtain a typical absorption spectrum of the water molecules. And obtaining the evolution data of the line width delta ν and the absorption area A of the absorption spectrum along with time through spectrum fitting.
Step 3), obtaining the environmental pressure P by inversion according to the calibration relation between the line width Deltav and the pressure P1Time evolution information of P1＝F-1(Δ ν), typical pressure inversion results, as shown in fig. 3.
Step 4), according to the calibration relation between the absorption area A and the pressure P, obtaining the corrected absorption area A through inversion1(ii) a Then, the corresponding mole fraction X is calculated and obtained by utilizing the calibration relation between the mole fraction X and the absorption area A1As shown in fig. 4;
A1＝G(P1)；
X1＝H-1(A1)＝H-1[G(P1)]。
step 5), known mole fraction X at calibration0And the calculated mole fraction X1To pressure P1Correcting to obtain corrected pressure P2Time evolution information of;
wherein r is the ratio of the self-broadening coefficient and the air broadening coefficient of the water molecules at the selected absorption spectral line, and can be obtained by querying a database; the broadening ratio r of the selected absorption spectral line can be obtained by inquiring a HITRAN2016 database to be 4.6, and the pressure P obtained after 1 st iteration correction is calculated2As shown in fig. 5.
Step 6), according to the calibration relation between the absorption area A and the pressure P, utilizing the pressure P after the 1 st iteration correction2Obtaining the corrected absorption area A by inversion2Then, the corresponding mole fraction X after 1 st iteration correction is calculated and obtained by utilizing the calibration relation between the mole fraction X and the absorption area A2As shown in fig. 6;
repeating the iteration steps to obtain the corrected pressure P of different iteration times nn+2And a mole fraction Xn+1As shown in fig. 6.
Iteratively correcting the mole fraction Xn+1The time evolution information of (a) is:
Xn+1＝H-1[G(Pn+1)]
iteratively corrected pressure P'n+2And mole fraction X'n+1The time evolution information of (a) is:
wherein n is 0,1,2,3 and is an integer;
it can be seen that the pressure and mole fraction data substantially converged after 4 iterative corrections. Generally, the pressure error obtained by two successive calculations is smaller than a set threshold value, generally 1%, that is, the corrected pressure and mole fraction data basically tend to converge.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the present invention.
Claims (5)
1. A correction method for pressure measurement based on TDLAS absorption method under high mole fraction is characterized by comprising the following steps:
step 1), calibrating to obtain a known mole fraction X0Under the condition, the calibration relation delta ν between the absorption spectrum line width delta ν and the pressure intensity P of the gas to be detected, the calibration relation A between the absorption area A and the pressure intensity P, G (P), and the relation A between the absorption area A and the mole fraction X of the gas to be detected under normal pressure, H (X);
step 2), performing absorption spectrum measurement on the gas to be measured to obtain absorption spectrum data, and obtaining evolution data of the line width delta ν and the absorption area A of the absorption spectrum along with time through spectrum fitting;
step 3), obtaining the environmental pressure P by inversion according to the calibration relation delta v between the line width delta v and the pressure P (F (P)1Time evolution information of;
P1＝F-1(Δν)；
step 4), according to the calibration relation A between the absorption area A and the pressure P, obtaining the corrected absorption area A through inversion1；
A1＝G(P1)；
Then utilizing the calibration relation between the mole fraction X and the absorption area AA ═ H (X), the corresponding mole fraction X is calculated1Time evolution information of;
X1＝H-1(A1)＝H-1[G(P1)]；
step 5) Using the known mole fraction X at calibration0And the calculated mole fraction X1To pressure P1Correcting to obtain corrected pressure P2Time evolution information of;
step 6), repeating the steps 4) and 5), and calculating the mole fraction X corrected by different iteration times nn+1Time evolution information and pressure Pn+2Until the pressure data is converged, the obtained pressure is the environmental pressure P of the gas to be measuredn+2；
Wherein n is 0,1,2,3 and is an integer.
2. The TDLAS absorption pressure measurement based correction method at high mole fraction of claim 1, wherein:
the iteratively corrected mole fraction Xn+1The time evolution information of (a) is:
Xn+1＝H-1(An+1)＝H-1[G(Pn+1)]
the iteratively corrected pressure Pn+2The time evolution information of (a) is:
wherein n is 0,1,2,3, and r is the aspect ratio of the gas to be measured.
3. The method of claim 1 for correcting TDLAS absorption based pressure measurements at high mole fractions, comprising:
and the pressure data is converged to be that the pressure error obtained after two continuous iterative corrections is smaller than a set threshold value.
4. The TDLAS absorption pressure measurement based correction method at high mole fraction of claim 3, wherein:
the threshold is 1%.
5. The method of claim 2 for correcting TDLAS absorption based pressure measurements at high mole fractions, comprising:
the broadening ratio r is the ratio of the self-broadening coefficient and the air broadening coefficient of the gas to be detected at a specific absorption spectral line and is obtained by inquiring a HITRAN2016 database.
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Patent Citations (6)
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