Collaborative Research: Molecular Growth in Time-varying, Non-premixed Flames

这是一项在强制时变火焰中分子生长化学的协调、全面的研究，涉及耶鲁大学和乔治华盛顿大学的研究小组。主要的物质浓度、小的自由基浓度、速度和温度是用一套基于激光的技术来测定的。较大的物种取样使用新型脉冲微探针耦合到质谱仪。实验工作补充了火焰结构的时间相关计算，包括分子生长化学。研究了三种时变非预混火焰：不发光的氮稀释甲烷火焰，40%乙烯-60%氮气火焰，稍发光，60%乙烯-40%氮气火焰，较发光。第一个火焰将为该方法提供一个基本案例和演示环境。稳定的“40/60”火焰沿中心线观察到最大的烟灰负荷，而“60/40”火焰在边缘附近显示最高的烟灰水平，这表明分子生长化学和包流体所经历的时间-温度历史之间存在微妙的相互作用。其目标是为竞争性烟尘生长模型的严格测试提供实验数据，并指导对该过程的直观理解的发展。对燃料热解和分子生长化学形成的大量中间碳氢化合物的浓度进行了时间分辨测量；这些四维数据与高保真的温度场和速度场相结合，以实验方式绘制了整个粒子起始过程；分子生长化学用三个最先进的烟灰形成化学模型进行数值模拟。更广泛的影响陆地燃烧产生的烟尘颗粒现已被认为对健康构成重大威胁，并已成为美国环保署严格的新法规的主题。从发动机设计师的角度来看，对烟灰的关注超越了这些监管问题。燃烧室初级区烟灰浓度高，导致燃烧室衬板的热辐射负荷高。烟灰涂层在衬板表面将大大提高下垫金属的温度。由于烟尘的产生对压力非常敏感，新燃烧器运行时的高压使这些问题更加严重。如果要控制烟尘及其相关问题，就必须以实验测量支持的计算模型的形式定量了解烟尘的生长和氧化机制。所提议的工作的一个重要组成部分将是对化学和机械工程的本科生和研究生的教育。此外，正在进行的K-12教育活动将通过教师研究经验（RET）计划继续进行并扩大。

This is a coordinated, comprehensive study of molecular growth chemistry in forced, time-varying flames involving groups at Yale and George Washington University. Major species concentrations, small radical concentrations, velocity, and temperature are determined using a suite of laser-based techniques. Larger species are sampled using a novel pulsed microprobe coupled to a mass spectrometer. The experimental work is complemented by time-dependent computations of flame structure that include molecular growth chemistry. Three time-varying, non-premixed flames are studied: a non-luminous, nitrogen-diluted methane flame, a40% ethylene-60% nitrogen flame that is slightly luminous, and a 60% ethylene-40% nitrogen flame that is more luminous. The first flame will provide a base case and demonstration environment for the approach. The steady "40/60" flame has been observed to have peak soot loadings along the centerline while the "60/40" flame shows highest soot levels near the edges, indicative of the subtle interplay between molecular growth chemistry and the time-temperature history experienced by a packet of fluid. The goal is to provide experimental data for a rigorous test of competing soot growth models, and also to guide the development of intuitive understanding of the process. Time resolved measurements of the concentrations are made for a host of intermediate hydrocarbons formed from fuel pyrolysis and molecular growth chemistry; these four-dimensional data are combined with high-fidelity temperature and velocity fields to map experimentally the entire particle-inception process; and molecular growth chemistry is simulated numerically using three of the most evolved soot-formation chemistry models available.Broader impactsCombustion-generated soot particulates from land-based sources are now acknowledged to pose a significant health risk and have been the subject of stringent new EPA regulations. From the standpoint of an engine designer, the concern about soot goes beyond these regulatory issues. High soot concentrations in combustor primary zones contribute to high thermal radiation loads on combustor liners. Soot coatings on liner surfaces will drastically increase underlying metal temperatures. These issues are exacerbated by the high pressures at which new combustors are operated, because soot production is very sensitive to the pressure. If soot and the problems associated with it are to be controlled, quantitative understanding of the soot growth and oxidation mechanisms in the form of computational models supported by experimental measurements is essential. An essential component of the proposed work will be education of undergraduate and graduate students in chemistry and mechanical engineering. Also, on-going activities in K-12 education will continue and be expanded through the Research Experience for Teachers (RET) program.