Quantitative Gas-Phase Scalar Mixing Measurements in Turbulent Spray Flows

1067625萨顿对于大多数实际的能量转换系统，液体燃料喷雾被喷射到氧化环境中;在氧化环境中，液滴必须分散、蒸发，并且燃料蒸气必须在化学反应之前与氧化剂分子混合。 尽管液体燃料燃烧室受到几个物理和化学过程的影响，但它最终还是受到液滴蒸发和随后的气相混合过程的限制。 虽然标量混合已被深入研究的单相湍流，目前的理解湍流喷雾内的气相混合过程是有限的，由于缺乏实验评估。 这主要是由于在液滴存在的情况下精确测量气相浓度的极端困难。 本研究的目的是开发，验证和应用一种新的基于激光的成像诊断实验研究蒸发和气相混合过程中的湍流喷雾流。 智力优势：目前的研究计划将涉及一种变化的过滤瑞利散射（FRS）技术的发展，以准确地成像燃料蒸气浓度场，而不受周围液相液滴的干扰。 这项研究计划的基础是一个系统的评估的准确性，灵敏度和局限性的建议FRS技术应用于湍流喷雾流。 与用于在液滴存在下检测燃料蒸气的先前技术相比，新的FRS方法提供了两个明显优点的潜力：（1）由于FRS的性质，所记录的信号可以明确地归因于蒸气，因为来自不想要的液相液滴的光散射可以使用单频激光源和光学厚的原子或分子过滤器的组合进行光谱过滤。 感兴趣的气相散射由于热多普勒效应而在光谱上加宽，并且该加宽的气相信息的一部分福尔斯落在分子过滤器的带宽之外并且被成功地传输到检测器。 (2)FRS技术不需要特定的荧光燃料或示踪剂，而是利用大多数燃料具有大的瑞利散射截面并且记录的信号取决于燃料蒸气和空气混合物的局部组成。 通过不使用荧光燃料示踪剂，避免了由于蒸馏效应引起的复杂化。 一旦验证，新的工具将被应用于了解液滴分散，蒸汽生产和气相（燃料蒸汽和空气）混合湍流蒸发喷雾之间的耦合。 所提出的诊断方法将是变革性的，因为对多相系统内的蒸发和混合过程的新的、基本的理解水平将从这种诊断的发展中产生，从而允许访问以前不可用的嵌入在液体喷雾中的气相过程。 还预计，新的基本测量湍流喷雾将证明是无价的建模社区更广泛的影响：适当的燃料-空气混合物的准备是至关重要的，以满足现代能源转换系统的性能目标，包括控制点火，火焰稳定性，效率和低污染物排放。 所提出的FRS技术提供了一个机会，获得一个新的，基本水平的理解的复杂的蒸发和湍流混合过程，需要作为一个积木，以了解高度湍流，多相条件下发现的现实发动机。 改进的基本理解为在实际平台内实现更有效和更可控的燃烧提供了机会。 在与研究相关的教育方面，博士研究生的研究将得到该项目的支持。 这项研究为直接教学和培训提供了独特的机会，并允许研究生在包括流体动力学和光学诊断在内的广泛的高级主题中工作（并做出重大贡献）。 该项目还将涉及本科生研究人员的参与，提供机会让最聪明的本科生参与研究生一级的研究，从而有助于扩大科技界合格毕业生的队伍。 将通过在公开文献中传播成果和在会议上介绍，为国家和国际学术和研究基础设施作出更多贡献。 通过将研究工作纳入研究生一级的教学，将对教育基础设施作出更多的贡献。

1067625SuttonFor the majority of practical energy-conversion systems, a liquid fuel spray is injected into an oxidizing environment; where the liquid droplets must disperse, evaporate, and the fuel vapor must molecularly mix with the oxidizer prior to chemical reaction. Although complicated by several physical and chemical processes, liquid-fueled combustors are ultimately limited by droplet vaporization and the subsequent gas-phase mixing process. While scalar mixing has been studied in-depth for single-phase turbulent flows, the current understanding of gas-phase mixing processes within turbulent sprays is limited due to the scarcity of experimental evaluation. This primarily stems from the extreme difficulty of accurately measuring vapor-phase concentrations in the presence of droplets. The objective of this research is the development, validation, and application of a new laser-based imaging diagnostic to experimentally investigate vaporization and gas-phase mixing processes in turbulent spray flows. Intellectual Merit: The current research program will involve the development of a variation of the Filtered Rayleigh Scattering (FRS) technique to accurately image fuel-vapor concentration fields without interference from the surrounding liquid-phase droplets. This research program is underpinned by a systematic assessment of the accuracy, sensitivity, and limitations of the proposed FRS technique as applied in turbulent spray flows. The new FRS approach offers the potential for two distinct advantages compared to previous techniques for detecting fuel vapor in the presence of droplets: (1) due to the nature of FRS, the recorded signal can be unambiguously due to vapor because the light scattering from the unwanted liquid-phase droplets can be spectrally-filtered using the combination of a single-frequency laser source and an optically-thick atomic or molecular filter. The gas-phase scattering of interest is spectrally-broadened due to thermal Doppler effects and a portion of this broadened gas-phase information falls outside of the molecular filter's bandwidth and is successfully transmitted to a detector. (2) The FRS technique does not require a particular fluorescent fuel or tracer, rather it takes advantage that the majority of fuels have large Rayleigh scattering cross sections and the recorded signal is dependent on the local composition of the fuel vapor and air mixture. By not using fluorescent fuel tracers, complications due to distillation effects are avoided. Once validated, the new tool will be applied to understand the coupling between droplet dispersion, vapor production, and gas-phase (fuel vapor and air) mixing in turbulent evaporating sprays. The proposed diagnostic approach will be transformative as a new, fundamental level of understanding of the vaporization and mixing processes found within multi-phase systems will result from the development of this diagnostic, allowing access to previously unavailable gas-phase processes embedded within the liquid spray. It is also anticipated that new fundamental measurements in turbulent sprays will prove invaluable to the modeling communityBroader Impacts: Proper fuel-air mixture preparation is critical for meeting performance objectives of modern energy-conversion systems including controlled ignition, flame stability, efficiency, and low pollutant emissions. The proposed FRS technique offers the opportunity to acquire a new, fundamental level of understanding of the complex vaporization and turbulent mixing processes that is needed as a building block to understand the highly turbulent, multiphase conditions found in realistic engines. An improved fundamental understanding offers the opportunity for more efficient and controlled combustion within practical platforms. In terms of research-related education, the Ph.D. research of a graduate student will be supported by this project. This research provides unique opportunities for direct teaching and training and allows the graduate student to work within (and significantly contribute to) a wide range of advanced topics including fluid dynamics and optical diagnostics. This project also will involve the participation of undergraduate student researchers, providing an opportunity to expose the brightest undergraduates to graduate-level research and thus helping to extend the pool of qualified graduates within the scientific and technological community. Additional contributions to the national and international academic and research infrastructure will be made through the dissemination of results into the open literature, and through presentations at conferences. Additional contributions to the educational infrastructure will be made by integrating the research efforts into teaching at the graduate level.