CN110823849B - Quantitative measurement method and device for transient combustion field - Google Patents
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Abstract
The invention designs a quantitative measurement method and a quantitative measurement device for a transient combustion field, and belongs to the technical field of combustion diagnosis. The device comprises: the system comprises a clock synchronization and delay triggering module, a tunable laser generating module, an optical fiber beam splitter, a lens group, a photoelectric detector array, a high-speed multi-path data acquisition module, a high-energy pulse laser generating module, an area array photoelectric detector, a control and calculation module and the like. Firstly, calibrating optical parameters of a laser-induced fluorescence testing system by using a steady-state combustion field; then, measuring the same section of the transient combustion field by using a calibrated device; and finally, substituting the low-resolution temperature distribution obtained by laser absorption spectrum tomography into the established laser-induced fluorescence calculation model to obtain the high-resolution temperature, the concentration distribution of the detected groups and the molecules. The invention combines laser-induced fluorescence and laser absorption spectrum, and has important application value for monitoring and diagnosing combustion field.
Description
Technical Field
The invention designs a method and a device for quantitatively measuring a transient combustion field, belongs to the technical field of combustion diagnosis, integrates a planar laser induced fluorescence technology and a laser absorption spectrum technology, and is used for quantitatively measuring the temperature of the transient combustion field, the concentration of intermediate product groups and the concentration of final product molecules.
Background
The temperature field of the combustion field and the measurement method of the fuel gas components can be mainly divided into a contact type and a non-contact type. The contact method mainly comprises a thermocouple temperature measurement method, a sampling analysis method and the like, and is easy to interfere a flow field, low in response speed and low in spatial resolution. The non-contact method mainly comprises an acoustic method, a spectrum method and the like, and the original state of a measured medium flow field is effectively ensured because the sensor is not in contact with the measured medium. Planar Laser Induced Fluorescence (PLIF), Laser Absorption Spectroscopy (LAS) are two important components in spectroscopic measurements.
The PLIF technology adopts ultraviolet or visible light wave band laser to form a sheet-shaped light beam, selectively excites free radicals or tracer particles in a combustion field to radiate fluorescence, and is one of the most important technical means for researching a flow field and a combustion field. PLIF is generally used to detect some important combustion intermediates (e.g., OH, CH) in a combustion field2O, NO, etc.) characterization of the sameTwo-dimensional distribution.
The qualitative PLIF technology can be used in the fields of visualization of combustion field spatial distribution, dynamic evolution of space-time distribution, measurement and visualization of difficultly-measured components, simultaneous measurement and visualization of multiple components and the like, and has the characteristic of high space-time resolution (time resolution nanosecond and space resolution micron order). Brackmann et al, 2014, in a paper entitled "Characterization of ammonia two-photon laser-induced fluorescence for gas-phase diagnostics" Applied Physics B "115 vol.1, 25-33 (Characterization of ammonia two-photon laser-induced fluorescence for gas-phase diagnostics) in Brackmann et al, measured and obtained CH groups and NH groups in ammonia-methane-air laminar and turbulent flames using a two-photon LIF technique3PLIF image of longitudinal section of molecule, CH group and NH were obtained3The distribution position of the molecules on the flame front. Zhou et al published in Combustion and flame 2014 (Combustion)&Flame)161, pp.6, 1566 and 1574, in the article "Strategy for single laser induced fluorescence formaldehyde imaging in turbulent methane/air Flame" (passage for PLIF single-shot HCO imaging in turbulent methane/air flames), PLIF was used to measure the distribution of free radical HCO in methane/air turbulent flames for indicating the heat release rate of hydrocarbon flames. PLIF techniques, however, present significant difficulties in quantitative measurements, primarily in that the PLIF signal is difficult to scale and susceptible to collision quenching effects. In order to solve the problems of the two problems, which are puzzled by the quantification of the PLIF technology, researchers have proposed various improved experimental methods based on the traditional technology for many years.
Such as scaled PLIF techniques. In the 1997 report on the two-dimensional laser-induced fluorescence for the Quantitative measurement of hydroxyl concentration fields (Quantitative measurements of OH concentration fields by two-dimensional laser-induced fluorescence), published by Arnold et al in Applied Physics B, volume 64, stage 5 579 and page 583 (Applied Physics B), the LIF technique was calibrated by laser absorption spectroscopy to measure the OH group concentration distribution in a methane/air premixed flat flame at different pressures, wherein the scaling factor for the OH group concentration was obtained by the absorption spectroscopy of one-dimensional pulsed ultraviolet light. In a study of quantitative concentration of hydroxyl in laminar flow plane flame (A student of quantitative concentrations of hydroxyl (OH) in laminar flow plane flame using planar laser induced fluorescence method), a academic paper of Jalbert in 2011 calibrates flame to be measured with standard flame, simplifies parameter calibration problem in quantitative measurement, measures change rule of OH group concentration in premixed plane flame of methane/air and hydrogen/air along with flame height, and studies influence of equivalence ratio and flow rate on OH group concentration. However, the calibration PLIF technology ignores the temperature field distribution difference between the standard flame and the flame to be measured to a certain extent and the fact that the collision quenching rate changes along with the change of the spatial position in the flame, and can only realize quantitative measurement to a certain extent, and the accuracy is low.
As with picosecond PLIF technology, the laser pulse width is less than the fluorescence collision quench lifetime. In 1996, Bormann et al, supra at 6, 601 and 607, respectively, in applied Physics B, 62, Single-pulse laser-induced fluorescence in atmospheric flame and Single-pulse collision-insensitive picosecond planar laser-induced fluorescence of atmospheric flame hydroxyl2Σ+(v' ═ 2) in tomosynthesis-compression flames) using monopulse picosecond PLIF technology to obtain CH at normal pressure4/O2The PLIF images of OH groups in the premixed flame, which are not related to the collision quenching effect, are properly mixed, the laser pulse width adopted in the experiment is 470ps, the camera width of a Charge-coupled Device (ICCD) is 400ps, and the relative concentration image of the OH groups is obtained in the experiment because the measured PLIF image is not calibrated. The defects are that the common laser is difficult to generate high-energy laser with picosecond magnitude, the gate width of an ICCD camera is difficult to reach the picosecond magnitude, and the practical engineering use is inconvenient.
And when the energy density of the exciting light is higher than the saturated excitation threshold energy density like the saturated LIF technology, the fluorescence signal is only related to the molecular number density, the stimulated absorption, the stimulated radiation and the spontaneous radiation process of the component to be detected and is not related to the energy of the exciting light and the collision quenching rate. Li et al, 2013, published in Combustion and flame (Combustion)&Frame) 160 Vol.1, 40-46, paper "Induction of fluorescence Using saturated laserAnd Probe sampling method for measuring the concentration of nitric oxide in an ammonia-doped methane/air flame (Measurements of NO concentration in NH)3-doped CH4+ air flame using structured laser-induced fluorescence and probe sampling) for the study of NO in nitrogen-containing fuelsxFormation and conversion of (1), measurement of NH incorporation using saturated LIF technique3CH (A) of4NO concentration in the after flame zone of the air premixed flame. The main disadvantages are that: it is often difficult to achieve the desired saturation excitation energy density with the laser output pulses, and thus, it is difficult to achieve two-dimensional quantitative measurements of constituent concentrations.
Researchers have also used bi-/multi-wire techniques for quantitative measurement of temperature fields, in combination with other techniques to achieve quantitative calibration of concentration fields. In the article Dual wavelength planar laser induced fluorescence for measuring temperature and composition in optical HCCI Engines with negative valve overlap (Dual-wavelength PLIF measurements of temperature and composition in an optical HCCI engine with negative valve overlap), tracer molecule 3-pentanone was added to fuel and air, and the temperature and composition distribution in homogeneous charge compression ignition Engines were measured using the two fluorescence spectra of 3-pentanone, but a homogeneous flame of known temperature, pressure, tracer molecule concentration distribution was still used in calibration experiments, published by Snyder et al in SAE International Journal of Engines (SAE International Journal of Engines)2 volume 1, phase 460, 474. Studies by Lenjin et al in 2016, paper "Effect of non-equilibrium plasma on Low pressure premixed Flame", published on papers 50-67, volume 165, Combustion and Flame (Combustion & Flame), part 1: in the hydrocarbon-based chemiluminescence, temperature and hydroxyl (Effects of non-equilibrium plasmas, part 1: CH chemiluminiscence, temperature, and OH), multiline OH-LIF was used to study the effect of non-equilibrium plasma on low-pressure premixed flame, the relative values of temperature field and OH concentration field were obtained using multiple fluorescence lines of the combustion intermediate OH, and then the concentration field was calibrated using single-pass laser absorption spectroscopy. However, simultaneous measurement of multiple lines of LIF for the same group generally requires multiple pulsed lasers, which increases system cost and optical path complexity. Although one pulsed laser can be time-tuned to different wavelengths, this is not practical for unsteady state combustion field measurements. In addition, the component concentrations need to be calibrated by means of single line laser absorption spectroscopy.
The LAS technique is based on the Beer-lambert absorption law. The laser intensity is influenced by various combustion products and tiny solid carbon particles contained in the combustion process in an absorption and scattering mode, but by adopting a laser absorption spectrum technology, the influence of the combustion products and the particles on the laser intensity is basically consistent in a quite wide frequency range no matter the laser intensity is attenuated due to absorption or scattering. The characteristic ensures that the laser absorption spectrum measurement technology is hardly influenced by the existence of combustion products and micro particles, and also ensures the accuracy of measuring the temperature and the component concentration of the combustion field by adopting the laser absorption spectrum technology. Gaseous molecules such as CO, CO2，H2O，NH3，CH4And the like have strong rotation and vibration absorption spectral lines in an infrared band and are commonly used as monitoring molecules. Since the seventies of the last century, researchers, represented by Stanford university R.K. Hanson, began to explore and study laser absorption spectroscopy, and in 1977, High-resolution spectroscopy for combustion gases (High-resolution spectroscopy of combustion gases using a tunable diode laser) was first conducted using a diode laser, published as Applied Optics (Applied Optics) at 2048 th 2045 th 2048.
LAS measurements are averaged along the optical path and therefore have low spatial resolution and do not meet the combustion diagnostic requirements of non-uniform, complex flow fields. In recent years, in order to improve the resolution of reconstruction of temperature and gas composition distribution on a single laser path, researchers such as Liu, etc. in 2012 published in Journal of the American society for aerospace, aviation and aerospace (AIAA Journal)45, Vol.2, pp.411 & 419 entitled "line-of-sight absorption Spectroscopy for measuring non-uniform temperature distribution" (Measurement of non-uniform temperature distribution using line-of-sight absorption Spectroscopy)Scanning multiple H's on a laser path2Absorption line of O, for on-path H2The non-uniform distribution of O is reconstructed to obtain the probability density distribution of temperature. Although this method obtains a temperature probability density on a single path, the temperature distribution is not clear, and it is not possible to correlate the temperature with the position.
In order to solve the problem, an LAS Tomography technology combining LAS and Tomography (CT) has attracted attention, and reconstruction inversion of temperature field and gas component distribution of a complex flow field can be achieved by acquiring LAS measurement information at a plurality of angles and a plurality of paths and combining with a CT algorithm. Some researchers have acquired multi-angle, multi-path experimental data using mechanical rotation/translation with the help of conventional CT imaging concepts. In 2005, Villarreal et al published in application Optics 44 vol.31, 6786, 6795, a Frequency-resolved absorption tomography with tunable diode lasers (Frequency-resolved absorption tomography with tunable diodes) focused on axisymmetric flames, reconstructed their temperature and component concentration distributions by passing a single laser through a flame generated by a translatable atmospheric flat flame burner, combined with the Abel inverse transformation. In 2010, Wangfei et al published in Measurement Science and technology (Measurement Science)&Technology) volume 21, No. 4, document No. 045301 entitled "tunable diode laser absorption spectroscopy for Two-dimensional tomography of gas concentration and temperature distribution" (Two-dimensional-tomography for gas concentration and temperature distribution) in the paper, four sets of lasers and detectors were used to achieve fast scanning of the flow field by means of four high-speed rotating stages, data required for reconstruction of each image were acquired within 100ms, and successfully applied to NH at laboratory conditions3And (4) rebuilding concentration. The method for acquiring multi-angle data by adopting mechanical translation/rotation and then reconstructing images is difficult to obtain high time resolution, and is only suitable for a steady flow field or a flow field with slow change. In order to give consideration to both spatial resolution and temporal resolution, temperature and component concentration are inverted by combining limited angle and measured data with image reconstruction algorithm with strong robustnessDistribution becomes an important research direction. In 2010 H.McCann et al, published in Journal of Chemical Engineering (Chemical Engineering Journal)158, vol.1, 2-10, paper "High-speed Chemical composition tomography in multi-cylinder automobile engine" (High-speed Chemical properties tomography in a multi-cylinder automobile engine), a tunable diode laser absorption spectrum tomography system is used for reconstructing an image of gas component distribution in an automobile engine cylinder, and the working condition in the cylinder is truly reflected. Hyperspectral tomography technology for temperature and H of J85engine tail nozzle plane published by L.Ma et al in 2013 in optical Express 21, vol 1, 1152 and 1162250kHz two-dimensional imaging of O concentration distribution (50-kHz-rate 2D imaging of temperature and H)2O confinement at the extreme plane of a J85engine using hyperspectral tomography) successfully applies the frequency agile absorption spectrum tomography technology to the reconstruction of the temperature distribution at the outlet of the GE J85 aircraft engine, and reduces the requirement of space sampling by using multispectral measurement. Xu Li Jun et al in 2015 developed a fan-shaped beam tomography sensor using tunable diode laser, which can be used for imaging of flame temperature field and component concentration field, and has high spatial and temporal resolution, the temporal resolution can be 5kHz, and the spatial resolution can reach 0.78cm, and the results are reported in optical quick report (Optics Express)23 vol.17, 22494 and 22511, Development of fan-shaped beam TDLAS-based fast temperature and gas concentration tomography sensor for rapid imaging of temperature and gas concentration. However, the laser absorption spectrum tomography system in the limited space is generally limited by the optical path layout, the number of projection angles is limited, the volume of the photoelectric detector determines the limited number of detectors in each projection direction, and the two determine the limited measurement data together, so that the flow field is measured by the fixed limited angle projection, and although the time resolution can reach kHz, the spatial resolution is not too high in the inversion mode by combining with the image reconstruction algorithm with strong robustness, and the micrometer-scale measurement accuracy has a larger difference compared with the PLIF.
Limitations of the separate detection methods of PLIF and LAS have resulted in deficiencies in each measurement technique. The traditional single-wavelength PLIF can realize high-resolution display of a temperature field and combustion intermediate product radicals, has great difficulty in quantitative measurement, and LAS tomography can realize quantitative measurement of the temperature field and the molecular concentration distribution of a combustion final product, but the spatial resolution is insufficient. The development of high-resolution, quantitative optical imaging is the trend in the combustion field diagnostic technology, and the fusion of PLIF and LAS tomography is a new approach to solve the above problems.
Based on the background, the invention provides a method and a device for quantitatively measuring a transient combustion field, which can obtain the quantitative temperature of the transient combustion field, the concentration distribution of intermediate product groups and final product molecules.
Disclosure of Invention
Aiming at the problems that the traditional single-wavelength PLIF technology is mainly used for measuring combustion intermediate product radicals, the resolution is high, and quantitative measurement is difficult; LAS tomography is mainly used for measuring combustion product molecules, and has low precision and high resolution; the invention discloses a transient combustion field quantitative measurement method and system based on fusion of plane laser induced fluorescence and absorption spectrum, which can obtain the temperature, intermediate product group and final product molecular concentration distribution of a quantitative high-resolution transient combustion field.
The technical scheme of the invention is as follows: firstly, optical parameters of the single-wavelength PLIF test system are calibrated by using a steady-state combustion field. For a stable combustion field, the temperature field and the component concentration field of the stable combustion field can be considered to be kept unchanged, a high-energy pulse laser generation module is tuned to two different excitation wavelengths of a measured group, the stable combustion field is shaped by a lens group to become a sheet light source to irradiate the same section, a picosecond/nanosecond ultra-narrow shutter area array photoelectric detector is adopted, the influence of quenching coefficient fluctuation on fluorescence intensity is eliminated by matching with an accurate delay control triggering technology, fluorescence intensity images under the two excitation wavelengths are shot, the intensity ratio is a function of temperature, the temperature field distribution is resolved, the concentration of the measured group is calibrated by using a single-path LAS, and finally the two-dimensional distribution of the temperature and the concentration of the measured group on the section is obtained. Then, using calibrated single wavelength PLIF test system andthe combination of LAS tomography, which gives a low resolution temperature field, with the measurement of the above mentioned cross-sections
Constituent concentrations of combustion end product molecules
Two-dimensionally distributed, low-resolution temperature field of
As a constraint condition of PLIF measurement results, a quantitative high-resolution temperature field T can be calculated by using an iterative solution algorithmtIntermediate radical concentration Nt。
The invention has the advantages that: aiming at the current situation that the PLIF is mainly used for intermediate product measurement and the LAS is mainly used for final product measurement, the two measurement modes are fused by using the parameter of the temperature field, the advantages of high-resolution PLIF measurement and high-precision LAS measurement are combined, and the technical problem that the single-wavelength PLIF in the unsteady combustion field cannot be quantitatively measured is solved.
Drawings
Fig. 1 is a block diagram of a measuring apparatus, which is composed of: the system comprises a clock synchronization and delay triggering module (1), a tunable laser generating module (2), an optical fiber beam splitter (3), a lens group (4), a photoelectric detector array (5), a high-speed multi-channel data acquisition module (6), a high-energy pulse laser generating module (7), a lens group (8), an area array photoelectric detector (9), a control and calculation module (10) and the like.
Fig. 2 is an embodiment diagram briefly describing a specific embodiment.
Detailed Description
The measuring system comprises a clock synchronization and delay triggering module, a tunable laser generation module, a photoelectric detector array, a high-speed multi-path data acquisition module, a high-energy pulse laser generation module, a lens group, an area array photoelectric detector, a control and calculation module and the like. The measuring method of the invention comprises the following steps:
the method comprises the following steps: calibrating optical parameters of the PLIF test system using a steady-state combustion field:
tuning high-energy pulse laser generation module to certain excitation wavelength lambda of detected group1The pulse laser generates laser pulse, the laser pulse is shaped by the lens group to become a sheet light source, the sheet light source penetrates through a certain section D of a stable flow field to be detected, the nanosecond/picosecond-level ultra-narrow shutter area array photoelectric detector is adopted, the accurate delay trigger control technology is matched, the influence of quenching coefficient fluctuation on fluorescence intensity is eliminated, and a fluorescence intensity image is obtained by shooting with the area array photoelectric detector:
wherein h is the Planck constant, v1Is the fluorescence frequency, Ω is the solid angle collected, A is the area of the region of the laser beam, l is the axial extension from where the fluorescence is found, N is the ground state concentration of the measured group, B12Is the Einstein coefficient, IvIs the splitting illumination of the laser light,
can be written as:
in the formula, J1Is the rotational energy level of the measured radical, B is the rotational constant of the measured radical, k is the Boltzmann constant, TcalIs the temperature; the formula (2) is substituted for the formula (1) and is obtained by arrangement:
tuning the high-energy pulse laser generation module to another excitation wavelength lambda of the detected group2And repeating the process on the same section D of the combustion field to obtain a fluorescence image:
wherein, v2Is the fluorescence frequency, J2Is the rotational energy level of the measured group;
the ratio of the measured fluorescence intensities at different excitation wavelengths was calculated:
at a fluorescence frequency v1、ν2Determining the rotational energy level J of the measured group1、J2Under the premise of determination, the fluorescence intensity ratio of the stable combustion field measured under different excitation wavelengths
Is a function of temperature and can be expressed as:
the two-dimensional distribution T of the temperature field with the same resolution of the planar array photoelectric detector is calculated by the formula (6)cal；
Selecting characteristic absorption spectrum line of the measured group, measuring the absorption rate A on a certain path L of the cross section D by using a single-path LAS,
S(Tcal(x) Is the line intensity of the absorption line at the transition, equation (7) can be discretized as:
where m denotes dividing the path traversed by the laser into m segments, LiIs the length of the i-th segment,
is the temperature of the i-th section,
the concentration of the detected group in the section i;
the temperature value T of each point on the absorption path L calculated by the combination formula (6)calDetermining the relative concentration of the path L by the formula (1) and the integral absorption rate on the path determined by the formula (8), calculating the concentration value of the measured group at each point of the path L, calculating the temperature value of each point of the combustion field plane obtained by the formula (6), determining the relative concentration relation by the formula (1) and the concentration value of the measured group at each point of the path L obtained by the calculation, and calculating the two-dimensional distribution N of the concentration value of the measured group in the section Dcal(ii) a Through the steps, the concentration N of the group component of the intermediate product in the steady-state flame combustion field is obtainedcalAnd temperature Tcal；
Step two: the same cross section is measured in the transient combustion field by combining single wavelength PLIF with LAS tomography:
keeping the plane of the PLIF sheet-shaped light beam and the LAS tomography cross section in the same section D;
tuning high-energy pulse laser generation module to excitation wavelength lambda of detected group1Measuring the intensity of fluorescence with an area array photodetector
Can be expressed as:
wherein N istIs the ground state concentration of the measured group, TtIs the transient temperature of the combustion field;
the formulas (1), (9) can be arranged as follows:
measured group NtThe concentration of (d) can be expressed as:
the value of the concentration of the measured group N according to formula (11)tIs dependent on the temperature measurement T of the corresponding locationtIt can be abbreviated as:
Nt＝Ψ(Tt) (12)
Ψ is a functional relationship defined by equation (11), which can be characterized as a monotonic function, and therefore an inverse function exists, expressed as:
Tt＝Ψ-1(Nt) (13)
when PLIF is measured, a LAS chromatographic imaging system is triggered by a clock synchronization and delay triggering module to measure the absorption spectrum of product molecules; tunable laser is generated by a tunable laser generation module, is divided into multiple paths by an optical fiber beam splitter, passes through a section D after being shaped by a lens group, transmitted light is emitted to a photoelectric detector array, and photoelectric signals are collected by a high-speed multi-path collection module and transmitted to a control and calculation module;
step three: iterative solution of quantitative high-resolution combustion field temperature T under the constraint of low-resolution temperature field obtained by LAS tomography calculationtIntermediate radical concentration NtThen T is addedtSubstituting into a chromatographic imaging model to calculate the concentration X of the final product moleculest：
A laser beam with a frequency v passes through a gas to be measured with a length l, a part of the light intensity is absorbed, and the absorption rate α (v) can be expressed as:
where P is total pressure, T (x) is temperature at x, X (x) is gas concentration at x, φ is a linear function, S (T (x)) is the line intensity of the absorption line at the transition, expressed as:
wherein, T0Is a reference temperature, v0The central frequency of a spectral line, h is a Planck constant, c is the speed of light, k is a Boltzmann constant, and E' the low-energy Q (T) of an absorption spectral line is a partition function, which reflects the ratio of the number of particles absorbing the corresponding low energy to the total number of particles at the temperature T;
since the linear function φ satisfies the normalization condition, i.e.
Integral a of the absorption a (v)vCan be expressed as:
using two different frequencies v1、ν2The ratio R of the integrated absorbances of the two absorption lines is a function of temperature only:
therefore, the expression for the average temperature on the laser path l can be found as:
wherein,
is the integrated absorption rate of the two absorption lines,
low level energy for two absorption lines;
on the basis of the calculated average temperature, the average gas concentration in the laser path can be expressed as:
in LAS tomography, the region of interest is divided into N grids, in the test module, the cross section D is divided into N grids, in each grid, the pressure, temperature and gas concentration can be considered as fixed values approximately, the laser beam passes through the region of interest and is detected by the photoelectric detector array, and M projection values, namely the absorption areas A of M absorption rates are obtainedv；
From the equation (16), the projection value A obtained by the ith laser beamikCan be expressed as:
wherein i and j denote the laser beam and the grid number, respectively, av,jRepresenting the locally integrated absorption in the j-th grid, i.e. Av(ii) a density of (d); l isijRepresenting the path length of the ith laser beam through the jth grid, equation (20) can be written as:
Lav＝Av (21)
where the M N matrix L is:
column vector av＝{av,1,av,2,…,av,N}T,Av＝{Av,1,Av,2,…,Av,M}T；
When the structural design of the system is determined, the optical parameters of the system are determined, L can be determined, and N grid internal integral absorption rates a are obtained through a solving formula (21)vBy two absorptionsSpectral line can be obtained
Instead of equation (18), the average temperature over the N grids can be found, i.e. a lower resolution temperature field is obtained
Will be provided with
By substitution of formula (19), the average temperature within the N grids can be obtained, i.e., the lower resolution of the final product molecular concentration field
Then, to
Spline interpolation is carried out to obtain the temperature field distribution T with high resolutiont,0Substitution of formula (12) to obtain a high-resolution intermediate concentration field distribution Nt,1(ii) a Will be provided with
Substituting an expression (13), and carrying out spline interpolation on the obtained result to obtain the high-resolution intermediate product concentration field distribution Nt,0Substitution of formula (13) to obtain a high-resolution temperature field distribution Tt,1；
Then an iterative solution is performed using equation (23),
until the iteration result satisfies the formula (24),
where norm is the vector norm and ε is the allowable error limit; at this time Tt,m+2、Nt,m+2I.e. the final temperature, intermediate radical concentration distribution, denoted as Tt、NtThe resolution is the resolution of the area array photoelectric detector;
further subdividing the LAS tomography grid into TtIs divided into Y grids, and the projection value A obtained by the i-th laser beam is obtained from the equation (16)ν,iCan be expressed as:
wherein i and j denote the laser beam and the grid number, respectively, av,jRepresenting the locally integrated absorption in the j-th grid, i.e. AvDensity of (D), Lhr,ijIndicating the path length, X, of the ith laser beam through the jth celljThe concentration of molecules in the jth grid, note Bij＝PS(T)Lhr,ijThen equation (20) can be written as:
BXt＝Av (26)
where, the M Y matrix B is:
column vector Xt＝{X1,X2,…,XY}T,Av＝{Av,1,Av,2,…,Av,M}T；
Solving the non-homogeneous linear equation system to obtain the component concentration distribution X of the final product molecules of the combustion fieldt。
The above description of the present invention and its embodiments is not limited thereto, and the drawings show only one embodiment of the present invention, and it is within the scope of the present invention that the structure or example similar to the technical solution is not creatively designed without departing from the spirit of the present invention.
Claims (1)
1. A quantitative measurement method of a transient combustion field comprises a clock synchronization and delay triggering module, a tunable laser generation module, an optical fiber beam splitter, a lens group, a photoelectric detector array, a high-speed multi-path data acquisition module, a high-energy pulse laser generation module, an area array photoelectric detector and a control and calculation module, and is characterized in that an optical parameter of a plane laser induced fluorescence test system is calibrated by utilizing a steady-state combustion field; then measuring the transient combustion field by using a single-wavelength plane laser induced fluorescence system and a laser absorption spectrum tomography system; finally, obtaining the quantitative high-resolution combustion field temperature T by using an iterative solution algorithmtDistribution, concentration of intermediate radical component NtDistribution, calculating the concentration X of final product molecule by combining with laser absorption spectrum tomography modeltDistributing; the method is characterized by comprising the following steps:
the method comprises the following steps: calibrating optical parameters of the plane laser-induced fluorescence testing system by using a steady-state combustion field:
respectively tuning a high-energy pulse laser generation module to two different excitation wavelengths lambda of a detected group1、λ2The high-energy pulse laser generation module generates laser pulses, the laser pulses are transformed into a sheet light source after being shaped by the lens group, the sheet light source penetrates through a certain section D of a stable flow field to be detected, a nanosecond/picosecond-level ultra-narrow shutter area array photoelectric detector is adopted, the influence of quenching coefficient fluctuation on fluorescence intensity is eliminated by matching with an accurate delay trigger control technology, and two fluorescence intensity images are obtained by shooting with the area array photoelectric detector:
and
where h is the Planck constant, c is the speed of light, v1、ν2Is the fluorescence frequency, Ω is the solid angle collected, A is the area of the laser beam, l is the area from the fluorescenceAxial extension of the site of discovery, NcalIs the concentration of the intermediate radical component, B12Is the Einstein coefficient, IvIs the laser splitting illuminance, J1、J2Is the rotational energy level of the measured radical, B is the rotational constant of the measured radical, k is the Boltzmann constant, TcalIs the temperature;
the ratio of the measured fluorescence intensities at different excitation wavelengths was calculated:
the two-dimensional distribution of the temperature field with the same resolution of the same area array photoelectric detector can be calculated;
selecting characteristic absorption spectrum line of the measured group, measuring the absorption rate alpha on a certain path L of the section D by using single-path laser absorption spectrum,
wherein P is total pressure, S (T)cal(x) Line intensity of the absorption line at the transition);
calculating the component concentration value of the measured group at each point on the path L by combining the formula (1), the formula (3) and the formula (4), further calculating the component concentration N of the intermediate product group in the section D according to the temperature value of each point of the section D calculated by the formula (3), the relative concentration relation determined by the formula (1) and the component concentration value of the measured group at each point of the path Lcal(ii) a Obtaining the concentration N of the intermediate product group component in the steady-state flame combustion field through the step onecalAnd temperature Tcal；
Step two: the single-wavelength plane laser induced fluorescence and laser absorption spectrum tomography are combined to measure the same section in a transient combustion field:
keeping the section of the planar laser induced fluorescence sheet beam and the section of the laser absorption spectrum tomography on the same section D; tuning tunable pulsed laser generation module to excitation wavelength lambda of detected group1Measuring the intensity of fluorescence with an area array photodetector
Can be expressed as:
wherein N istIs the concentration of the group component of the intermediate product of the transient combustion field, TtIs the combustion field temperature, the equations (1), (5) can be collated as:
wherein, phi (T)t,Nt) Is Tt，NtThe ratio of the fluorescence intensities is determined by N according to equation (6)t、Tt；
Triggering a laser absorption spectrum tomography system by a clock synchronization and delay triggering module, and measuring a product molecular absorption spectrum while performing plane laser induced fluorescence measurement;
step three: iterative solution of quantitative high-resolution combustion field temperature T under the constraint of low-resolution temperature field obtained by laser absorption spectrum tomography calculationtDistribution, concentration of intermediate radical component NtDistributing, then TtSubstituting into a chromatographic imaging model to calculate the concentration X of the final product moleculestDistribution:
in laser absorption spectroscopy tomography, a region of interest is divided into N grids, a laser beam passes through the region of interest and is detected by a photodetector array, and M projection values, i.e., absorption areas A of M absorptances, are obtainedvIt can be expressed as:
Lav＝Av (7)
wherein the mxn matrix L ═ L (L)ij)M×NI and j denote the laser beam and the grid number, respectively, LijRepresenting the path length of the ith laser beam through the jth grid, column vector av＝{av,1,av,2,...,av,N}T，Av＝{Av,1,Av,2,...,Av,M}T，av,jDenotes the locally integrated absorption in the jth grid, Av,iAn absorption area representing an i-beam laser absorptance;
by means of two absorption lines, one can obtain
Then calculating the temperature in each grid by using the ratio of two local integral absorptances in each grid to obtain the temperature field distribution with low resolution
To pair
Spline interpolation is carried out to obtain the temperature field distribution T with high resolutiont,0Substituting into formula (6) to obtain high-resolution intermediate product concentration field distribution Nt,1(ii) a Will be provided with
Substituting an expression (6), and carrying out spline interpolation on the obtained result to obtain the high-resolution intermediate product concentration field distribution Nt,0Substituting into the formula (6) to obtain the temperature field distribution T with high resolutiont,1；
Then an iterative solution is performed with equation (8),
until the error of the iteration result is less than the set value, T at the momentt,m+2、Nt,m+2I.e. the final temperature and the concentration distribution of the intermediate product group components, namely the temperature T of the combustion fieldtDistribution, concentration of intermediate radical component NtDistribution, the resolution of which is the resolution of the area array photoelectric detector;
the grid of laser absorption spectrum tomography is further subdivided into Y grids and Q is recordedij＝PS(T)Lhr,ijP is the total pressure, S (T) is the line intensity of the absorption line at the transition, Lhr,ijRepresenting the path length of the ith laser beam through the jth grid, there is a tomographic model:
QXt＝Av (9)
wherein, M rows and Y columns matrix Q ═ (Q)ij)M×YColumn vector Xt＝{X1,X2,...,XY}T,XjIs the concentration of molecules in the jth grid;
distribution of temperature TtSubstituting into Q, solving the non-homogeneous linear equation set (9) to obtain the concentration X of the final product moleculestAnd (4) distribution.
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