Collaborative Research: Effect of Chemistry and Molecular Transport on Tubular Premixed Flames

这项研究使用先进的激光诊断技术和详细的计算机模拟，分析了管状几何结构中高度弯曲、稀薄、预混合的火焰的结构。研究的燃料是氢、甲烷和丙烷。管状预混火焰，预混反应物径向向内流动，形成拉伸的柱状火焰，是曲率和拉伸数值研究的理想基本构型。管状构型可以在数学上简化为两点边值问题，其中包含复杂化学和详细分子传输的解决方案可以在短时间内在个人计算机上确定。这项研究使用了一种独特的光学可访问管式燃烧器，该燃烧器结合了用于高级激光诊断(例如，拉曼散射和荧光)应用的光学端口。最近对贫氢-空气管状火焰中气体成分和温度的拉曼测量表明，在低拉伸值时与计算结果非常一致。然而，在高拉伸时，巨大的理论数据差异表明，需要改进接近熄灭的稀薄管状火焰的化学和/或分子传输模型。这项工作利用先进的激光诊断技术和结合了详细传输和复杂化学的数值模型来研究稀薄预混管状火焰。对近消光管状火焰进行了研究，以确定分子输运和化学机理对模型数据比较的影响。研究主要集中在火焰半径与火焰厚度之比接近1的高曲率火焰上。为了改变刘易斯数效应，研究了不同的燃料。采用弧长延拓法对消光条件进行了准确的预测。建立了管状火焰的全二维模型，以检验近熄灭时的自相似假设。最后，对预混管状火焰与表面的相互作用进行了研究，对微型燃烧室的设计具有一定的指导意义。更广泛的影响这项研究将范德比尔特大学先进的激光诊断实验室和耶鲁大学最先进的燃烧模拟小组的能力结合在一起。包括少数族裔在内的研究生和本科生参与了这项研究。稀薄燃料/空气预混在汽油燃料汽车和甲烷燃料燃气轮机发电中产生清洁和高效的燃烧。实际装置中的稀薄预混火焰被湍流拉伸和弯曲，但很少有人对曲率和拉伸的影响进行全面的实验和数值研究。以前的大多数研究都集中在拉伸平面预混火焰上。预混火焰中的曲率很重要，因为差动扩散和曲率的结合会对火焰的温度、气体成分和污染物的形成产生很大影响。曲率可以延缓或促进火焰的熄灭，弯曲火焰可以存在于标准稀薄可燃极限以下；升华。火焰有望在高效率的情况下产生非常低的污染物排放。学生们将在研究会议上展示他们的成果。学生将接触到最新的计算机模拟和激光诊断设备。教师将指导初中生和高中生学习工程学。。

This study analyzes the structure of highly curved, lean, premixed flames in the tubular geometry using both advanced laser diagnostics and detailed computer simulations. Fuels studied are hydrogen, methane, and propane. A tubular, premixed flame, where premixed reactants flow radially inward to form a stretched cylindrical flame, is an ideal fundamental configuration for the numerical study of curvature and stretch. The tubular configuration can be mathematically simplified to a two-point boundary-value problem where solutions incorporating complex chemistry and detailed molecular transport can be determined in a short time on a personal computer. The study uses a unique optically accessible tubular burner that incorporates optical ports for application of advanced laser diagnostics (e.g., Raman scattering and fluorescence). Recent Raman measurements of gas composition and temperature in lean hydrogen-air tubular flames show excellent agreement with calculations at low stretch values. However at high stretch, large theory-data discrepancies point to the need for improvement in chemical and/or molecular-transport modeling in lean tubular flames near extinction. This work studies lean premixed tubular flames with advanced laser diagnostics and numerical models incorporating detailed transport and complex chemistry. Near-extinction tubular flames are studied to determine the effects of molecular transport and chemical mechanism on the model-data comparisons. The studies focus on high-curvature flames where the flame radius to flame thickness is near unity. To vary Lewis number effects, various fuels are studied. The arc-length continuation method is used to properly predict the extinction condition. A full two-dimensional model of the tubular flame is developed to check the self-similarity assumption near extinction. Finally, the premixed tubular flame interaction with surfaces is studied with implications for design of micro-combustors. Broader Impact This study unites the capabilities of an advanced laser diagnostics laboratory at Vanderbilt University and a state-of-the-art combustion simulation group at Yale University. Graduate and undergraduate students including underrepresented minorities are involved in the research. Lean fuel/air premixing produces clean and efficient combustion in gasoline-fueled automobiles and methane-fueled gas turbines for electric power generation. Lean premixed flames in practical devices are stretched and curved by turbulence but there are few comprehensive experimental-numerical studies of the effects of both curvature and stretch. Most previous studies have focused on stretched planar premixed flames. Curvature in premixed flames is important as the combination of differential diffusion and curvature can greatly affect the flame temperature, gas composition, and pollutant formation. Flame extinction can be retarded or promoted by curvature and curved flames can exist below the standard lean flammability limit; sublimit. flames have the promise of producing very low pollutant emission at high levels of efficiency. Students will present their results at research conferences. Students will be exposed to the latest computer simulation and laser diagnostic facilities. Faculty will mentor junior and senior high-school students in engineering. .