Temperature is one of the most important parameters for understanding reaction process in high-temperature reactive flows such as aeroengine combustion and plasma flows. CARS is an effective temperature measurement method, but significant challenges persist due to spectral distortions caused by intense spectral interference. Existing methods for non-resonant background suppression used in tracer imaging are fail to satisfy the stringent spectral reconstruction accuracy requirements essential for temperature retrieval. Therefore, an iterative variation-based simultaneous baseline correction and temperature inversion method is proposed, and corresponding accuracy is verified using measured CARS spectra with different type backgrounds at temperature ranging from 1000 K to 2300 K, indicating that the maximum relative deviation is 5.23%. The temperatures of combustion and plasma flows are measured using the proposed method. For combustion flow, the maximum temperature retrieval error is reduced from 28.57% to 2.56%. For plasma flow, the non-resonant background is separated, and a vibrational temperature of 1796 K and a rotational temperature of 846 K are obtained, indicating that the plasma is in thermal non-equilibrium state. The use of simultaneous baseline correction and temperature inversion method enables accurate thermometry for a wide range of high-temperature combustion and non-equilibrium plasma flows under significant spectral interference.

Are wind tunnels are crucial ground-based test facilities for simulating atmospheric re-entry and conducting thermal protection tests for hypersonic vehicles, Accurately obtaining the internal flow field temperature and enthalpy of are heater. which is the core component of an are wind tunnel, is the foundation for evaluating the flow field quality, performance and optimization design of are wind tunnels, as well as ensuring the effectiveness of wind tunnel tests. The composition and specific enthalpy characteristics of are plasma are theoretically analyzed, the contributions of internal energy, ionization energy and thermodynamic potential energy to the total specific enthalpy of the plasma are investigated. The results show that the contribution of internal energy increases with temperature and dominates at temperatures below 11 000 K. The contribution of ionization energy rapidly rises to become dominant around 11 000 K due to the ionization of argon atoms and tends to level off around 15 000 K. and increases again around 20 000 K due to the further ionization of Ar+ ions to form Ar(++ )ions. The contribution of thermodynamic potential energy is the smallest, and its growth pattern is strongly correlated with the changes in composition, both showing a significant in-crease with the formation of new ions through ionization, An optical emission spectra measurement system is established, and the temperature and enthalpy of the arc plasma are calculated based on the measured spectra, then the efficiency of the are heater is obtained. Under the experimental conditions, when the current increases from 60 to 120 A. the temperature and specific enthalpy of the arc plasma increase from 14 859 K and 48.89 MJ kg to 17 617 K and 55.96 MJ(-1) kg, respectively. However, due to the increase in the are constriction radius with increasing current, which led to an enhanced convective heat transfer with the wall, and the increase in padiative heat loss due to the elevated plasma temperatures with increasing current, both of which exceeded the increase in plasma enthalpy, resulting the efficiency of the are heater decreases from 0.73 to 0. 37.

A dual-polarization spontaneous Raman spectroscopy measurement system based on volume phase holographic transmission grating (VPH) has been developed, which enables synchronous quantitative measurement of the concentration and emperature of major gaseous species components (carbon dioxide CO oxygen Os nitrogen N water H.O. fuel. and Intermediates) under a single laser pulse in a combustion field. The temperature obtained synchronously can correct the influence If temperature on the Raman scattering cross-section of species. Two sets of ICCD cameras synchronously collect Raman cattering signals in two mutually perpendicular directions. effectively eliminating fluorescence interference. This system can also chieve joint testing technology of Rayleigh temperature measurement and Raman concentration measurement. The Joncentration and temperature were calibrated on the gas sample pool with controllable pressure and temperature and the McKenna standard burners the temperature measurement accuracy is less than 1.06% and the accuracy of component concentration measurement is less than 1. 10%. In the combustion field of an aero-engine model combustion chamber, the simultaneous measurement for a single pulse (20 ns) of component concentration and temperature at three multi-measurementpoints in a single working condition was completed.

How to characterize thermodynamic non-equilibrium characteristics of flow field accurately and reliably is the key to solving the thermal and chemical non-equilibrium problem,which is one of the most basic scientific problems in hypersonic aerodynamcis.Based on the principles of coherent anti-Stokes Raman scattering(CARS)and modified exponential gap(MEG)Raman linewidth model,a CARS spectral computation and vib-rotational temperature inversion program is proposed for characterizing the thermodynamic non-equilibrium properties of high-temperature gas flow field.The influence of vibrational temperature and rotational temperature on Raman linewidth and CARS spectral characteristics are studied theoretically.A CARS system is built and the corresponding accuracy in a wide temperature range is verified in a static environment that is established by using a high-temperature tube furnace and a McKenna burner.The results show that the average relative deviation of the vibration temperature Tv and rotational temperature Tr from the equilibrium temperature Teq are 4.28%and 3.34%respectively in a range of 1000 to 2300 K,and the corresponding average repeatability is 1.95%and 3.03%respectively.These results indicate that the vibrational temperature and rotational temperature obtained by the non-equilibrium program are in good agreement with those obtained from the thermal equilibrium program.Finally,a non-equilibrium microwave plasma flow is built and its vibrational temperature and rotational temperature are obtained by using the developed program.The results show that the microwave plasma is in thermodynamic non-equilibrium,and the vibrational temperature and rotational temperature are proportional to microwave power,while the thermodynamic non-equilibrium degree exhibits an opposite trend.With microwave power increasing from 80 to 180 W,the vibrational temperature of plasma increases from(2201±43)K to(2452±56)K,the rotational temperature increases from(382±20)K to(535±49)K,for which the principal reasons are that the increase in microwave power leads to an increase in electron number density,and neutral particles obtain energy through collision with electrons,resulting in the increase of vibrational temperature,rotational temperature,and translational temperature.The thermodynamic non-equilibrium degree decreases from 0.83 to 0.78 with the microwave power increasing,which is due to the V-T relaxation rate increasing.The molecules in the excited vibrational states lose energy through collision with ground state molecules(i.e.V-T relaxation process),leading the vibrational energy to be converted into translational energy.For N2 molecules,the V-T relaxation rate is directly proportional to the temperature,which causes the difference between vibrational temperature and rotational temperature to decrease with microwave power increasing,and non-equilibrium degree to decrease with microwave power increasing as well.

The construction of a high-temperature gas calibration source is of great significance since it can provide an effective high-temperature experimental environment for, e.g. verifying high-temperature measurement techniques and studying high-temperature combustion mechanisms. Here, we try to obtain a high-temperature gas field on a multi-jet burner by controlling the gas supplies to it. We use OH planar laser-induced fluorescence (OH-PLIF) to observe the compositional uniformity of the field and coherent anti-Stokes Raman scattering (CARS) to investigate the temperature uniformity of the field. We find from OH-PLIF images that the distribution of OH between the adjacent jets becomes more uniform with the increasing flow rate of CH 4 , and the flow rate of the co-flow N 2 around jets also affects the uniformity of OH distribution. The measured temperature distribution by CARS is consistent with the OH distribution. At the jet outlet location, the temperature distribution had a periodic variation and gradually became more uniform with the height increased from the jet outlet. We find that the flow rate of CH 4 and co-flow N 2 and the radiative heat transfer rate play an important role in temperature distribution for the multi-jet burner. Also, the results show that a wide range of temperatures can be constructed by regulating the recipe of the gas supplies, and the highest temperature achieved in this work is 2457 K.

In this paper, a pulsed cavity-ring down spectroscopy ( CRDS) is employed to measure the quantitative concentration of the OH radical in a plane flame burner with premixed methane/air. By analyzing the cavity ring-down absorption spectrum theory, we select the P-1 (2) absorption line spectrum of the electronic transition band OH A(2)Sigma(+) -X-2 Pi(0,0) and build a set of the pulsed CRDS experimental device with a laser wavelength of 308. 6 nm. The device of the pulsed CRDS is composed of a pair of mirrors with a reflectance of 99. 7%, the cavity length of the ring-down cavity is 270 cm, and the ring-down time of the empty cavity (without a flame in the optical cavity) is 2. 33 mu s. By analyzing the experimental parameters that affect the precise measurement of concentration, we use Planar Laser Induced Fluorescence (PLIF), Coherent Anti-Stokes Raman Scattering (CARS) and the pulsed CRDS to measure the effective absorption length of OH, high temperature of the flame, and cavity ring-down time. When the premixed methane (1. 1 L center dot min(-1)) and air (15 L center dot min(-1)) are burned in a flat flame burner, and at the height of 6 mm from the burner surface, the precisely measured effective absorption length by PLIF is 7. 1% higher than that of directly choosing the diameter of the burner surface as the absorption length, the measured precision of the temperature by CARS is increased by 45% than that measured by the thermocouple under room temperature, the measured precision of the optical cavity ring-down time with flame in the cavity and non-OH absorption wavelength is improved by 21. 6% than that measured time of cavity ring-down without a flame in the cavity. By combining the above measurement techniques to measure all experimental parameters precisely, we obtain that the number density of OH molecules (3. 59 X 10(13) molecules center dot cm(-3)) can reach the maximum value when the height from the furnace burner is 6 mm, and the precision of OH concentration is 35. 6% higher than that of the unmodified OH concentration. Under different equivalence ratios (Phi=0. 7 similar to 1. 1), with the increase of the height from the burner surface, the number of OH particles gradually decreases, and the curve fitting shows that the OH concentration decreases in an e-exponential decay. At the same combustion height, the concentration of OH increases with the increase of equivalent ratios. When the methane flow rate is kept constant, the OH concentration in the oxygen-rich combustion condition is higher than in the low-oxygen combustion condition. In the combustion field, the precise measurement method with the multi-spectral technology (CRDS-CARSPLIF) can achieve the precise quantitative measurement of OH concentration and provide technical support for the quantitative measurement of the concentration of other combustion product molecules, which plays a crucial role in the study of combustion chemical reactions.

In this paper, we mainly investigate the error of thermocouples in different combustion environments by comparing the measured temperatures by CARS (coherent anti-Stokes Raman spectroscopy). In the experiment, we build a set of broadband and unstable-resonator spatially enhanced detection CARS devices to achieve precise temperature measurement. By comparing the measured temperatures by CARS and thermocouples in an adiabatic environment, we find that the temperatures measured by both are well matched. In an open environment, we find that the measured temperature by thermocouples has large errors compared to that by CARS and literature temperature, which is primarily caused by thermal radiation, and there is an error of about 7% by using the double-thermocouple correction method, and we propose the measured temperature by CARS as the true value to correct the radiation error of thermocouples and use the least-squares method to fit the temperature curve, resulting in an error of only 0.83%. In addition, we realize a wide-range precise temperature detection from 1100 to 2100 K by CARS, and the relative standard deviation and the relative error in the whole experiments are less than 1.8% and 1.6%, respectively.

针对当前喷气式涡轮航空发动机的主流稳焰方式-旋流火焰的燃烧机理、火焰构型等热点问题,设计加工了一套受限空间下的旋流燃烧器,利用了一种能够实现非侵入式、精细化、可视化复杂燃烧流场的OH-PLIF(OH-planar laser-induced fluorescence)测量系统,研究了该燃烧器在空气流量40 L/min时不同当量比的燃烧工况,并重点分析了旋流火焰的极限熄火工况.结果表明:在受限燃烧室内,由于壁面的作用旋流火焰从"V"型火焰发展成"M"型火焰,在主焰中心两侧会形成两个主漩涡,主漩涡的边界区域有较高浓度的OH分布;距离主纵截面的偏移量D越大,两个主漩涡的形状逐渐不稳直至完全消失,OH也逐渐向靠近壁面的区域聚集;旋流火焰的横向截面测量结果与纵向截面存在较强的对应关系,在H=5 mm横截面处,OH高度集中在"中心圆"区域,随着测量高度的上升,OH逐渐向燃烧室X轴方向两侧的壁面区域聚集.

为研究航空煤油全氟己酮燃烧抑制过程中OH自由基的变化规律,设计带有光学开窗的杯式燃烧器,以OH-PLIF技术为测量手段,利用2种不同波长的"差分法"测量方法克服了航空煤油燃烧场中碳烟、煤油及燃烧裂解大分子化合物对OH自由基荧光信号的干扰问题,获得了12组不同全氟己酮体积分数条件下的OH基分布特征图,对研究全氟己酮的抑制机理具有重要的参考意义,为理论模型的建立提供了基础数据.试验结果表明:对于OH基分布的垂直高度值H,在全氟己酮处于较低体积分数时(＜3.91%),H值缓慢增长,但随着体积分数的持续增加,H值会快速下降,随后逐渐趋于平缓;而对于OH基分布带的厚度值D和OH分布区域的占比S,随着全氟己酮体积分数的增加,两者呈现明显下降趋势.

The imaging experiment of Methylidyne (CH) radical generated from methane combustion on a swirl burner was carried out using Planar Laser Induced Fluorescence technology (PLIF), and the C-X (0,0) band was selected as the excitation method. The laser wavelength and laser energy have a significant impact on the signal strength and signal-to-noise ratio of CH radical, and the imaging quality of CH reached the best with the laser wavelength and energy are of 314.415 nm and 0.3 mJ. The fluorescence signal of CH radical from swirling flame mainly distributed on the outside of the image and exists in a narrow area. As the of equivalence ratio of methane combustion increased, the signal of CH radical gradually strengthened, and the flame profile of chemiluminescence gradually evolved from "V" type to "M" type, and the number of vortices formed by CH radical from PLIF imaging gradually increased.

中国空气动力研究与发展中心设备设计与测试技术研究所在国内首次搭建了基于标模发动机的10 kHz高频OH-PLIF试验系统,并于2021年5月在高超声速冲压发动机技术重点实验室的脉冲燃烧风洞上开展了超燃冲压发动机燃烧室测量试验研究.