A New Method for Imaging Mixture Fraction in Turbulent Non-premixed Flames

湍流非预混燃烧的燃烧模型的改进受到缺乏复杂反应系统中混合物分数及其耗散测量的严重限制。目前，最高保真度的混合物分数测量是从拉曼/瑞利散射推断的，但是这些测量难以应用于可能存在壁、烟灰或颗粒的更实用的燃烧环境中。我们建议开发一种新的技术，有望使空间和时间分辨成像的保守标量在湍流反应流，并可以应用于更广泛的环境比替代技术。这种新技术基于使用惰性气体（例如，Kr或Kr），其被引到燃料或氧化剂流中。稀有气体在燃烧时是惰性的，因此可以被视为守恒标量。稀有气体LIF测量给出了守恒标量的摩尔分数，但是需要温度测量和状态关系来推断混合物分数（即，源自燃料流的原子的质量分数）。我们的主要目标如下：（i）提高我们对该技术的局限性的理解，特别是关于对假定状态关系的需要，（ii）确定该技术是否可以应用于高级烃燃料，其中激光束吸收、荧光干扰和猝灭可能增加额外的困难，（iii）联合收割机与粒子图像测速技术（PIV）相结合，获得重要的、唯一的火焰混合分数/速度相关数据;（iv）研究双光子激光诱导荧光作为一种可供选择的守恒标量;以及（v）探索将惰性气体LIF与过滤的瑞利散射相结合，以获得存在颗粒/烟灰/壁时的同时温度场。智力优势：拟议的工作作为其目标的进一步发展的一种新的诊断技术，它有希望使测量混合物的分数和非预混燃烧系统中的耗散。主要的守恒标量是氪，虽然氙将被研究。组合的双光子LIF将使保守的标量测量在更多的应用流，如密闭燃烧室，或在流动的颗粒。这一特点将使人们能够将联合收割机混合物分数成像与PIV相结合，并有可能在含有烟灰或烟灰前体的流动中进行保守测量。它也可以有效地用作一种技术，用于研究混合/燃烧的安全问题排除使用有毒气体markers.Broader影响：这种新技术有望使测量混合物分数（或相关的替代保守标量）在燃烧环境中，这种测量以前是不切实际的，如燃气轮机，内燃机，火灾和超音速燃烧室。惰性气体LIF可能比替代技术更容易实现，并且该技术可能会在学术界，政府和工业中得到更广泛的应用。该技术提供的数据可能会影响先进燃烧模型的准确性，从而影响广泛的技术，包括利用可持续燃料的技术。随着计算工程的巨大进步，我们不能忽视验证计算的重要性，这将要求我们维护和开发实验基础设施，以获取所需的数据。

1134020ClemensThe improvement of combustion models for turbulent non-premixed combustion is severely limited by the lack measurements of mixture fraction and its dissipation in complex reacting systems. Currently, the highest fidelity mixture fraction measurements are inferred from Raman/Rayleigh scattering, but these measurements are difficult to apply in more applied combustion environments where walls, soot or particles may be present. We propose to develop a new technique that holds promise for enabling space- and time-resolved imaging of a conserved scalar in turbulent reacting flows, and which can be applied in a wider range of environments than alternative techniques. This new technique is based on using two-photon laser-induced fluorescence (LIF) of a noble gas (e.g., Kr or Xe), which is seeded into the fuel or oxidizer stream. Noble gases are inert in the presence of combustion and so can be treated as a conserved scalar. The noble-gas LIF measurement gives the mole fraction of the conserved scalar, but a temperature measurement and state relationship are required to infer the mixture fraction (i.e., mass fraction of atoms originating in the fuel stream). Our main objectives will be the following: (i) to improve our understanding of the technique's limitations, particularly regarding the need for an assumed state relationship, (ii) to determine if the technique can be applied with higher-hydrocarbon fuels where laser beam absorption, fluorescence interference and quenching may add additional difficulties, (iii) to combine the technique with particle image velocimetry (PIV) to obtain important and still unique mixture-fraction/velocity correlation data in flames, (iv) to investigate two-photon Xe LIF as an alternative conserved scalar, and (v) explore combining noble-gas LIF with filtered Rayleigh scattering to obtain simultaneous temperature fields when particles/soot/walls are present. Intellectual Merit: The proposed work has as its objective the further development of a new diagnostic technique, which holds promise for enabling measurements of mixture fraction and its dissipation in non-premixed combustion systems. The main conserved scalar of interest is krypton, although xenon will be investigated. The combined two-photon LIF will enable conserved scalar measurements to be made in more applied flows, such as confined combustors, or in flows with particles. This feature will enable one to combine mixture fraction imaging with PIV, and potentially to make conserved measurements in flows with soot or soot precursors. It also can be effectively used as a technique for studying mixing/combustion where safety concerns preclude the use of toxic-gas markers.Broader Impacts: This new technique holds promise for enabling measurements of mixture fraction (or a related surrogate conserved scalar quantity) in combustion environments where such measurements were previously not practical, such as gas-turbines, IC engines, fires, and supersonic combustors. Noble-gas LIF is potentially much easier to implement than alternative techniques and it is likely that the technique will see much wider use in academics, government and industry. The data that can be provided by the technique could potentially impact the accuracy of advanced combustion models and therefore impact a wide-range of technologies including those that utilize sustainable fuels. As great strides are made in computational engineering, we must not lose sight of the importance of validating the computations and this will require that we maintain and develop the experimental infrastructure that enables the acquisition of the needed data.