Collaborative Research: Molecular Growth in Forced, Time-varying Flames

这是一个协调的，全面的研究分子生长化学在强制，随时间变化的火焰涉及组在耶鲁大学和乔治华盛顿大学。 主要物种的浓度，小自由基的浓度，速度和温度确定使用一套基于激光的技术。 较大的物种采样使用一种新的脉冲微探针耦合到质谱仪。 实验工作的补充，包括分子生长化学的火焰结构的随时间变化的计算。 研究了三种随时间变化的非预混火焰：不发光的、氮气稀释的甲烷火焰、稍微发光的40%乙烯-60%氮气火焰和更发光的60%乙烯-40%氮气火焰。 第一个火焰将为该方法提供一个基本案例和演示环境。 已经观察到稳定的“40/60”火焰沿中心线沿着具有峰值烟灰负载，而“60/40”火焰在边缘附近显示出最高的烟灰水平，这表明分子生长化学和流体包经历的时间-温度历史之间的微妙相互作用。 其目标是提供实验数据的竞争烟尘增长模型的严格测试，并指导直观的理解过程的发展。 时间分辨测量的浓度是由燃料热解和分子生长化学形成的中间烃的主机，这些四维数据与高保真度的温度和速度场相结合，以映射实验的整个粒子的初始过程;和分子生长化学模拟使用三个最先进的煤烟形成化学模型可用。更广泛的影响燃烧-现在已经认识到，由陆地来源产生的煤烟颗粒对健康构成重大危险，并且已经成为严格的新EPA法规的主题。 从发动机设计者的角度来看，对烟尘的关注超出了这些监管问题。燃烧室主燃区中的高烟灰浓度导致燃烧室衬套上的高热辐射负荷。 衬管表面的烟灰涂层会大大增加底层金属的温度。 这些问题由于新燃烧器运行时的高压而加剧，因为烟灰的产生对压力非常敏感。如果要控制烟尘和与之相关的问题，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是必不可少的。 拟议工作的一个重要组成部分将是化学和机械工程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）计划继续并扩大。

Summary 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.