LIPF法对甲烷空气火焰温度及OH分布场的测量

 介绍了激光感生预分离荧光法(LIPF)的原理及一维与二维测量实验装置。利用可调谐KrF准分子激光器,在甲烷 空气火焰中测得了燃烧中间产物OH的系列荧光谱线及OH分子的二维荧光图象,对它的谱线结构进行了分析,并给出了燃烧火焰的一维温度值,测量的相对误差小于3%。二维荧光图象也定性表明燃烧火焰的OH分子密度分布和二维温度场等信息。     

利用平面激光诱导荧光技术测量燃烧场内NO的浓度分布

 介绍了平面激光诱导荧光的原理及实验装置，利用可调谐OPO激光器，在甲烷 空气火焰及一些高能燃剂燃烧火焰中测得了NO分子在不同压力、不同燃烧时刻的系列荧光谱线及二维浓度分布，并给出实验结果分析。     

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。     

预混湍流3D火焰面密度和燃料消耗率的估计

利用平面激光诱导荧光(OH-PLIF)技术测量了CH_4/air预混湍流火焰前锋面结构,通过图片处理得到了测量平面上的二维火焰面密度。基于不同的假设建立了三种不同模型,利用二维探测得到的火焰面信息来估计三维火焰面密度在测量面上的值,通过积分三维火焰面密度估计值得到燃烧系统的燃料消耗率。结果表明,预混湍流火焰前锋面为凹凸的褶皱结构,平面测量的二维火焰面密度明显低估了真实的火焰面密度,利用模型估计得到的3D火焰面密度对2D值有明显的改善。燃烧系统的燃料消耗率可以用来评估模型的可靠性,结果表明模型的误差都在40%以内。     

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。     

瑞利散射/激光诱导荧光技术用于空气、O2流场的二维瞬态测量

研究了空气分子的瑞利散射光强及真空紫外激光（波长１９３ｎｍ）诱导Ｏ２荧光强度与温度、密度的关系,给出了一般表达式。指出了可用于测量高速窃据流场中的瞬态密度和温度二维分布。利用带像增强的ＩＣＣ相机获得了室内空气及Ｏ２喷流的瑞利散射及激光诱导氧气荧光流场图像,图像处理后获得了流场的二发布参数。     

基于正交PLIF技术来评估2D火焰图像在反映锥形火焰3D结构方面的有效性（英文）

通过对平面激光诱导荧光(PLIF)图像进行分析,可以获得湍流火焰中的火焰面密度(Σ)、火焰刷厚度和湍流燃烧速度等关键参数,通过二维火焰图像及火焰参数可建立三维火焰模型。但目前二维PLIF图像能否精确反映三维火焰结构尚不明晰。该研究用正交PLIF技术测量了甲烷/空气预混湍流火焰横截面(垂直于火焰传播方向)和纵截面(平行于火焰传播方向)上的二维OH分布,然后通过对OH-PLIF图像的分析计算了火焰两截面的Σ,并分别比较了不同燃烧器出口速度、火焰不同位置和不同燃空当量比条件下,火焰两截面的Σ的差别。实验结果表明,在相同条件下,火焰纵截面的Σ均比火焰横截面的Σ偏小,其差值大小与燃烧器出口速度,火焰位置和燃空当量比相关。这一现象说明,最常采用的二维PLIF技术,在精确反映三维火焰结构时具有一定的局限性。     

四—（对—羟基苯基）卟啉在水／三氟乙酸溶液中J—聚集的光谱研究

本文研究了四－（对－羰基苯基）卟啉（ＴＣＰＰ）在Ｈ２Ｏ／ＣＦ３ＣＯＯＨ、Ｈ２Ｏ／ＣＣＩ３ＣＯＨ和Ｈ２Ｏ／ＣＨ３ＣＯＯＨ溶液中的ＵＶ－Ｖｉｓ吸收光谱、荧光光谱和拉曼光谱。实验表明,ＴＣＰＰ在Ｈ２Ｏ／ＣＨ３ＣＯＯＨ和Ｈ２Ｏ／ＣＣＩ３ＣＯＯＨ溶液中以分子态的Ｎ－质子化卟啉Ｈ８ＴＣＰＰ＾２＋存在,而在Ｈ２Ｏ／ＣＦ３ＣＯＯＨ中则形成Ｈ８ＴＣＰＰ＾２＋的Ｊ－聚集体。Ｊ－聚集体显示,ＵＶ－Ｖｉｓ吸收光谱和荧光光     

激光诱导荧光技术测量OH自由基的建立和研究

氢氧自由基（ＯＨ）在对流层大气化学中起着重要的作用,因此,对其浓度的测量具有重要意义。本文利用气体扩张激光诱导荧光技术（ＦＡＧＥ）建立了ＯＨ测定系统,对其进行了标定,得到归一化荧光信号（Ｓ）与ＯＨ自由基浓度的较好的相关关系,并对可能存在的干扰进行了分析。     

图象处理技术用于发光火焰温度分布测量的研究

一、前言 火焰温度的测量是一个难题,发光火焰温度分布的测量则更加困难。现有的各种测温方法都难以直接用来测量发光火焰的温度分布,故本文提出采用图象处理法测定发光火焰,特别是煤粉火焰的温度分布。火焰图象是工业燃烧宏观、整体过程的充分反映,也是控制燃烧的直接观察对象。通过对发光火焰图象信息的分析、处理和计算可获取其温度和温度分布,进而可求得反映燃烧状态的其他特征。     

激光诱导预分离荧光法窄带及宽带测温实验研究

介绍了激光诱导预分离荧光法测温的原理及实验结果。利用可调谐KrF准分子激光器 ,在常压甲烷 空气火焰内测得了OH自由基的系列荧光谱 ;并对它们的谱线结构进行了分析 ;给出了利用窄带激光和宽带激光两种不同激励条件下测量的温度值。通过选择适当的激励线及激光能量 ,减去背景噪声等途径 ,使两种方法的测量精度均高于 3 %。     

Experimental and numerical investigation of microscale hydrogen diffusion flames

Characteristics of microscale hydrogen diffusion flames produced from sub-millimeter diameter (d = 0.2 and 0.48 mm) tubes are investigated using non-intrusive UV Raman scattering coupled with LIPF technique. Simultaneous, temporally and spatially resolved point measurements of temperature, major species concentrations (O₂, N₂, H₂O, and H₂), and absolute hydroxyl radical concentration (OH) are made in the microflames for the first time. The probe volume is 0.02 × 0.04 × 0.04 mm³. In addition, photographs and 2-D OH imaging techniques are employed to illustrate the flame shapes and reaction zones. Several important features are identified from the detailed measurements of microflames. Qualitative 2-D OH imaging indicates that a spherical flame is formed with a radius of about 1 mm as the tube diameter is reduced to 0.2 mm. Raman/LIPF measurements show that the coupled effect of ambient air leakage and pre-heating enhanced thermal diffusion of H₂ leads to lean-burn conditions for the flame. The calculated characteristic features and properties indicate that the buoyancy effect is minor while the flames are in the convection–diffusion controlled regime because of low Peclet number. Also, the effect of Peclet number on the flame shape is minor as the flame is in the convection–diffusion controlled regime. Comparisons between the predicted and measured data indicate that the trends of temperature, major species, and OH distributions are properly modeled. However, the code does not properly predict the air entrainment and pre-heating enhanced thermal-diffusive effects. Therefore, thermal diffusion for light species and different combustion models might need to be considered in the simulation of microflame structure.     

Two-photon predissociative fluorescence of H2O by a KrF laser for concentration and temperature measurement in flames

Two-photon laser-induced predissociative fluorescence (LIPF) of H₂O is examined as a potential measurement technique of H₂O concentration and temperature in flames. Two-photons of 248 nm light from a narrowband KrF laser excite H₂O to the highly predissociative state in a hydrogen-air flame. The subsequent bound-free emission is observed from 400–500 nm in the flame at temperatures of 1000–2000 K and is found to be free of fluorescence interference from other flame species. This LIPF signal is not affected by collisional quenching due to the short lifetime of the predissociative state (2.5 ps). Broadband laser dispersion spectra, narrowband laser dispersion spectra, laser excitation spectra and probability density functions of the H₂O fluorescence are obtained in the hydrogen flame. The H₂O LIPF signal is found to be temperature sensitive and a two-line LIPF technique is needed for concentration and temperature measurement. The accuracy of a two-line LIPF technique for H₂O concentration and temperature measurement is determined.     

Investigation of non-premixed flame combustion characters in GO_2/GH_2 shear coaxial injectors using non-intrusive optical diagnostics

Single-element combustor experiments are conducted for three shear coaxial geometry configuration injectors by using gaseous oxygen and gaseous hydrogen(GO2/GH2) as propellants. During the combustion process, several spatially and time- resolved non-intrusive optical techniques, such as OH planar laser induced fluorescence(PLIF), high speed imaging, and infrared imaging, are simultaneously employed to observe the OH radical concentration distribution, flame fluctuations, and temperature fields. The results demonstrate that the turbulent flow phenomenon of non-premixed flame exhibits a remarkable periodicity, and the mixing ratio becomes a crucial factor to influence the combustion flame length. The high speed and infrared images have a consistent temperature field trend. As for the OH-PLIF images, an intuitionistic local flame structure is revealed by single-shot instantaneous images. Furthermore, the means and standard deviations of OH radical intensity are acquired to provide statistical information regarding the flame, which may be helpful for validation of numerical simulations in future. Parameters of structure configurations, such as impinging angle and oxygen post thickness, play an important role in the reaction zone distribution. Based on a successful flame contour extraction method assembled with non-linear anisotropic diffusive filtering and variational level-set, it is possible to implement a fractal analysis to describe the fractal characteristics of the non-premixed flame contour. As a result, the flame front cannot be regarded as a fractal object. However, this turbulent process presents a self-similarity characteristic.     

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。     

Heat release rate as represented by [OH] × [CH2O] and its role in autoignition

Data from a recent instantaneous, simultaneous, high-resolution imaging experiment of Rayleigh temperature and laser induced fluorescence (LIF) of OH and CH₂O at the base of a turbulent lifted methane flame issuing into a hot vitiated coflow are analysed and contrasted to reference flames to further investigate the stabilization mechanisms involved. The use of the product of the quantified OH and semi-quantified CH₂O images as a marker for heat release rate is validated for transient autoigniting laminar flames. This is combined with temperature gradient information to investigate the flame structure. Super-equilibrium OH, the nature of the profiles of heat release rate with respect to OH mole fraction, and comparatively high peak heat release rates at low temperature gradients is found in the kernel structures at the flame base, and found to be indicative of autoignition stabilization.     

Experimental analysis of local flame extinction in a turbulent jet diffusion flame by high repetition 2-D laser techniques and multi-scalar measurements

In this paper, we present a detailed experimental study of turbulence chemistry interactions in the “DLR_B” turbulent jet diffusion flame. The flame operates on mixtures of CH₄, H₂, and N₂ in the fuel stream at Re = 22,800 and is a target flame within the TNF workshop. Extinction and re-ignition events can be tracked in real time and related to the underlying flow field phenomena and temperature fields. Time resolved measurements of OH radical concentration fields are performed in combination with temperature and velocity field measurements. For this purpose, we combined high repetition rate (33 kHz) PLIF imaging with stereoscopic PIV and double pulse Rayleigh imaging techniques. Comparisons are made with results from multi-scalar Raman/Rayleigh/LIF point measurements that reveal the thermochemical state of the flame. The large deviations from equilibrium observed on resulting OH/temperature joint pdfs could be related to strain rate and Damköhler number variations caused by turbulent flow structures leading to frequent extinctions. The 2D measurement series uniquely reveal the underlying mechanism that can lead to such events. Finally, comparisons are made to strained laminar flame calculations, which are generally found to be in good agreement with the measured data.     

Effect of velocity gradient on propagation speed of tribrachial flames in laminar coflow jets

The effect of velocity gradient on the propagation speed of tribrachial flame edge has been investigated experimentally in laminar coflow jets for propane fuel. It was observed that the propagation speed of tribrachial flame showed appreciable deviations at various jet velocities in high mixture fraction gradient regime. From the similarity solutions, it was demonstrated that the velocity gradient varied significantly during the flame propagation. To examine the effect of velocity gradient, detail structures of tribrachial flames were investigated from OH LIF images and Abel transformed images of flame luminosity. It was revealed that the tribrachial point was located on the slanted surface of the premixed wing, and this slanted angle was correlated with the velocity gradient along the stoichiometric contour. The temperature field was visualized qualitatively by the Rayleigh scattering image. The propagation speed of tribrachial flame was corrected by considering the direction of flame propagation with the slanted angle and effective heat conduction to upstream. The corrected propagation speed of tribrachial flame was correlated well. Thus, the mixture fraction gradient together with the velocity gradient affected the propagation speed.