LIPS技术测量CH_4/空气预混火焰温度

简述了激光诱导偏振光谱技术的测温原理和实验方法,并利用激光诱导偏振光谱技术测量了常压CH4/空气预混火焰的温度分布。该技术灵敏度高,且不受碰撞猝灭的影响,适于诊断各种实际的燃烧过程。通过研究激光能量与信号强度的关系,获得了激光功率密度与信号强度的关系曲线以及实验中的最佳激光功率密度;记录并测量了燃烧场中OH分子A2∑＋-X2Π（0,0）跃迁带中P 1（2）和Q 1（8）两条吸收线的强度,用双线法计算了相应的温度,给出了CH4/空气预混火焰中不同化学配比条件下燃烧场温度的空间分布,实验结果与CARS的测量结果吻合较好。     

燃烧产物组成激光诱导荧光光谱的测量

对激光诱导荧光（LIF）光谱技术在燃烧过程中的应用进行研究，介绍测量燃烧过程中常见自由基OH和NO的LIF光谱的实验方案，以及采用激光诱导荧光光谱技术测量小分子荧光光谱的方法，利用YAG激光器、染料激光器、CO2激光器、光谱仪、ICCD等设备对燃烧产物中常见小分子自由基OH和NO进行了测量，从实验中得到了自由基OH和NO的荧光光谱。实验结果表明，荧光光谱与激发波长无关，但是激发波长改变后，荧光强度因离开最佳波长而有所下降，这符合分子荧光光谱的特征。与其他光谱技术相比，激光诱导荧光光谱技术具有极高的选择性和灵敏度。     

基于紫外可调谐激光吸收光谱技术的甲烷/空气平面预混火焰温度测量研究

火焰温度是燃烧领域最重要的宏观物理量之一,使用紫外可调谐激光吸收光谱技术,以火焰中的OH自由基作为测量对象对甲烷/空气平面预混火焰进行了温度测量。首先使用平面激光诱导荧光(PLIF)技术对甲烷/空气平面预混火焰不同燃烧工况条件下火焰中的OH基分布进行了测量,选取火焰中OH基分布均匀工况进行了紫外吸收光谱温度测量。通过LIFBASE仿真计算,综合考虑温度测量灵敏度、测量信噪比等因素,选择OH基A-X(0,0)吸收带中的P_1(2)和Q_1(8)两支谱线作为被测跃迁。测量时使用Nd∶YAG激光器泵浦染料激光器,经倍频后输出308~311nm紫外可调谐激光。通过染料激光器以0.4pm为步长进行激光波长调谐,分别扫描获得两条吸收谱线的吸收峰线型。对实验数据进行voigt拟合后,通过计算两条谱线的积分吸收值之比,获得了平面预混火焰中的温度信息。分别测量了燃烧器表面不同水平位置与燃烧器中心不同高度处的火焰温度。测量结果与文献报道的采用同样结构燃烧器,通过其他光谱技术获得的测量结果进行了横向对比。在OH基浓度较高的火焰锋面区域测温结果吻合度较高,验证了该技术测量结果的可信度。由于其测量对象与双线OH-PLIF测温的一致性,该技术未来可作为局部温度测量方法,进一步应用于对双线PLIF等二维火焰温度空间分布测量结果的标定当中。     

燃烧场参数的激光诊断技术研究

 介绍了燃烧场参数的激光诊断技术的研究进展，给出了用自发拉曼散射、激光诱导荧光、相干反斯托克斯拉曼散射法诊断燃烧场温度和组分的实验系统和部分实验结果，单次测量火焰的温度和组分浓度相对误差小于10%；利用平面激光诱导荧光技术获得了稳定燃烧场二维OH荧光图像，并分析了激光作用区域火焰二维温度场的分布。     

显示OH浓度分布图像的平面激光诱导荧光技术

用平面激光诱导荧光 (PLIF)技术测量平面火焰炉、狭缝火焰炉的单脉冲激光诱导OH荧光。由平面荧光图可得到氢氧基相对浓度分布和它的宽度。对于扩散火焰 ,高温区在OH带内侧 ;而对于预混火焰 ,二者基本一致。湍流火焰的PLIF图则清晰地显示出火焰面的不规则性。氢氧基的PLIF图像是研究火焰结构和流场的有力工具。     

二维偏振光谱技术对燃烧场的诊断

利用单脉冲激光诱导偏振光谱技术测量了甲烷/空气预混火焰、酒精灯火焰和固体燃剂燃烧场中OH的二维分布。简述了激光诱导偏振光谱技术的基本原理和二维测量的实验方法;通过测量火焰中OH自由基A~2∑~+-X~2∏(0,0)跃迁带中Q1(8)吸收线的强度,获得了燃烧场中OH的二维分布。实验结果对了解火焰构造,研究燃烧机理等有一定的参考价值。     

激光诱导荧光光谱燃烧测温技术研究

基于分子激发态振动能级粒子碰撞能量弛豫过程的理论,本文提出了一种可望实现瞬态燃烧温度测量的新技术——激光诱导分子热助振动荧光光谱技术。建立了分于激发态振动能级粒子碰撞能量弛豫过程的四能级系统模型,以BaCl分子为对象实验研究了激光诱导热助振动荧光光谱的特性,通过以5170波长选择激发BaCl的C~2Ⅱ_(1/2)(v=1)←→)X~2∑(v=0)能级跃迁,对液化石油气/空气预混火焰温度进行了实验测量。     

LIPS技术探测CH4/空气火焰中的OH自由基

论述了激光诱导偏振光谱技术的基本原理,实验方法及其对燃烧场的测量结果.利用光谱扫描方法获得了A2∑ -X2Ⅱ(0,0)跃迁带系列吸收谱线及P1(2)谱线的线型轮廓.测量了CH4/空气预混火焰不同化学配比、不同空间位置OH自由基的相对分布.实验中通过设计精密旋转调节装置有效提高了信噪比.     

平面激光诱导荧光实验中激励激光的光束整形

分析了激励激光光强分布对平面激光诱导荧光（PLIF）实验中荧光强度的影响。基于柱面微透镜列阵设计了一套激光片状光束匀滑整形系统,并根据PLIF实验的具体要求,通过光线追迹方法优化了系统参数。建立了片状光束整形实验系统,对染料激光进行了匀滑整形,获得了不均匀性〈4%的均匀片状光束,满足了PLIF实验所需。在此基础上建立了PLIF实验系统,获得了酒精灯火焰和CH4/air预混火焰中OH的二维荧光分布。     

水雾作用下富燃料甲烷预混火焰化学发光特性

利用阶梯光栅光谱仪与自行研制的水雾协流管式燃烧器,对富燃料甲烷/空气层流预混火焰化学发光特性进行实验研究.分析了锥形预混火焰燃烧过程中火焰面OH、CH以及C2自由基粒子光谱强度分布规律,以及水雾协流作用下的预混火焰发射光谱特性,探讨了水雾液滴对富燃料甲烷预混火焰发射光谱的影响.实验结果表明:当水雾量充足时,作用于内锥火焰阵面的水雾液滴使得火焰阵面OH、CH以及C2自由基粒子发射光谱强度减弱,抑制预混火焰燃烧;当作用于火焰面的水雾载荷比较小时,富燃料预混火焰的OH、CH的发射光谱强度得到一定程度的增强.     

Application of spontaneous Raman and Rayleigh scattering and 2D LIF for the characterization of a turbulent CH4/H2/N2 jet diffusion flame

4 /H₂/N₂ diffusion flame. Important aspects of the measuring technique, such as accuracy, cross talk between different Raman bands, and the correction procedure for background from laser-induced fluorescence are discussed. In addition, a 2D LIF and Rayleigh imaging system were used to study the structures of OH, CH, NO, and temperature distributions in the flame. A comparison between two different CH detection schemes is presented. A main goal of the investigations was a detailed and accurate characterization of the investigated flame as well as the study of experimental techniques. Joint pdfs of the temperature and major species concentrations were determined at nearly 100 measuring locations covering the complete flame. Parts of the results are presented in the paper in order to discuss effects of differential diffusion, flame extinction, and interaction between flow field and chemistry. The measured data sets which are available on the Internet are well suited for testing and validating mathematical flame models. Received: 8 July 1997/Revised version: 23 October 1997     

Absolute radical concentration measurements in low-pressure H2/O2 flames during the combustion of graphite

Absolute CN and CH radical concentrations were determined in situ during the combustion of a graphite substrate in premixed, laminar, low-pressure, H₂/O₂ flames for two different equivalence ratios, = 1.0 and = 1.5. For CN measurements, a small amount of NO (1.8%) was added. The concentration of CN was measured by cavity ring-down spectroscopy (CRDS) probing the absorption of the P_1,2 (13) in the B–X (0, 0) band at 388.1 nm, and the concentration of CH was measured by linear unsaturated laser-induced fluorescence (LIF) exciting the fluorescence of the R₁ (4) in the B–X (0, 0) band at 387.4 nm. Temperature measurements were done based on LIF excitation spectra of OH in the A–X (0, 0) band. It was found that the graphite substrate reduces the flame temperature in the vicinity of its surface. The CN concentrations were found to be three times higher for the rich flame than for the stoichiometric flame. CH concentrations were slightly higher for the stoichiometric flame than for the rich flame. The observed CH/CN concentration ratio is substantially lower compared to NO-doped low-pressure CH₄/O₂ flames. The obtained quantitative information can serve as a first calibration point for detailed numerical simulations of the burning solid graphite, which are based on the concept of surface elementary reactions.     

Correction of LIF temperature measurements for laser absorption and fluorescence trapping in a flame

A computational method is described in order to correct OH LIF temperature measurements for absorption of laser energy and trapping of fluorescence. Calculations are performed in a large range of flame conditions and can be used as a correction data base both in case of (0-0) and (1?0) excitations. Comparison of corrected temperatures profiles obtained in a 40 Torr methanol/air flame, for both kinds of Laser-Induced Fluorescence (LIF) excitations shows a very good agreement. This method is applied to measure the temperature profile of a methanol flame perturbed by a sampling probe. The LIF collection volume is located at the actual probe sampled volume using an experimental procedure already described. Spatial resolution and sensitivity of temperature measurements are sufficiently efficient to highlight, for the first time by LIF, an indubitable cooling effect due to the probe presence that induces important OH profile change. According to flame chemical modelling, it is shown that both effects are strongly correlated.     

Spectroscopic observations of methane-pulverized coal flames

A premixed laminar flame burner was used to study physical and chemical effects of burning methane and pulverized coal simultaneously. Spectral emissions obtained as a function of height in the flame, for OH, CH, C₂, and CO were used to calculate excited state species number densities. Premixed methane-air flames with a number of equivalence ratios and methane-air-coal dust flames with three equivalence ratios were studied and differences were noted. Spatial temperatures were measured in all flames by means of a thermocouple probe.The introduction of a pulverized coal additive (30mg/min) leads to changes in OH, Ch, C₂, and CO number densities and temperature at various heights, which depend on the stoichiometry of the methane-air flame. Possible chemical and physical mechanisms responsible for these changes are discussed qualitatively. The data pose a severe test for any quantitative model which includes the fluid dynamics, gas-phase chemistry, heterogeneous processes, and radiation transport.     

紫外脉冲激光退火发次对KDP晶体抗损伤性能的影响

在R-on-1的辐照模式下, 利用355 nm的紫外脉冲激光以低于KH₂PO₄ (KDP)晶体零概率损伤阈值的通量对其进行不同发次的全域扫描, 目的是为了研究KDP晶体在接受不同发次的紫外激光辐照后其抗损伤能力的变化规律及机制. 辐照后的1-on-1损伤测试表明, 适当的紫外激光退火可以有效地提升KDP晶体的抗损伤能力, 提升的幅度与其接受激光扫描的次数有关. 通过荧光和紫外吸收检测深入探讨了晶体内缺陷对激光退火的影响, 结果表明: 紫外脉冲激光辐照后KDP 晶体内的氧空位电子缺陷的存在与否是导致其抗损伤能力变化的主要原因; 通过拉曼和红外光谱的测量表明, 辐照后KDP 晶体内的PO₄, P–OH和P＝O基团的极化变形也导致了其抗损伤能力的改变. 关键词： 激光退火 荧光 拉曼 红外