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

这项研究分析了结构的高度弯曲，倾斜，预混火焰的管状几何形状，使用先进的激光诊断和详细的计算机模拟。 研究的燃料是氢、甲烷和丙烷。 预混反应物径向向内流动形成拉伸圆柱形火焰的管状预混火焰，是曲率和拉伸数值研究的理想基本构型。管状配置可以在数学上简化为两点边界值问题，其中可以在个人计算机上在短时间内确定包含复杂化学和详细分子输运的解决方案。 该研究使用了一种独特的光学可访问的管状燃烧器，该燃烧器包含用于先进激光诊断应用的光学端口（例如，拉曼散射和荧光）。 最近的拉曼测量的气体成分和温度在贫氢-空气管状火焰显示出良好的协议与计算在低拉伸值。然而，在高拉伸，大的理论数据的差异点需要改进的化学和/或分子输运模型在贫油管状火焰接近灭绝。 这项工作研究贫油预混管状火焰与先进的激光诊断和数值模型，结合详细的运输和复杂的化学。 近熄灭管状火焰进行了研究，以确定分子输运和化学机理的模型数据比较的影响。研究的重点是高曲率火焰的火焰半径火焰厚度接近统一。 为了改变刘易斯数效应，研究了各种燃料。 采用弧长延拓法对灭弧条件进行了预测。 一个完整的二维模型的管状火焰的发展，以检查自相似假设近熄灭。 最后，预混管状火焰与表面的相互作用进行了研究与微型燃烧室的设计的影响。这项研究结合了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。 研究生和本科生，包括代表性不足的少数民族参与了研究。 稀薄燃料/空气预混合在汽油燃料汽车和用于发电的甲烷燃料燃气轮机中产生清洁和高效的燃烧。 在实际装置中，贫油预混火焰被湍流拉伸和弯曲，但很少有全面的实验和数值研究的曲率和拉伸的影响。 以前的研究大多集中在拉伸平面预混火焰。 曲率在预混火焰中是重要的，因为微分扩散和曲率的组合可以极大地影响火焰温度、气体成分和污染物形成。 火焰熄灭可以通过弯曲来延迟或促进，弯曲火焰可以存在于标准稀薄可燃极限以下;次极限。火焰有希望在高效率水平下产生非常低的污染物排放。 学生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。 教师将指导初中和高中学生在工程。.

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. .