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

本研究利用先进的激光诊断和详细的计算机模拟分析了管状几何形状中高度弯曲、倾斜、预混火焰的结构。研究的燃料有氢、甲烷和丙烷。管状预混火焰，其中预混反应物径向向内流动，形成一个拉伸的圆柱形火焰，是曲率和拉伸数值研究的理想基本配置。管状结构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个人计算机上短时间内确定。该研究使用了一种独特的光学可及的管状燃烧器，该燃烧器集成了用于先进激光诊断（例如拉曼散射和荧光）的光学端口。最近的拉曼测量的气体成分和温度在稀薄的氢气-空气管火焰显示极好的一致性计算在低拉伸值。然而，在高延伸范围内，大量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。这项工作研究贫预混管火焰与先进的激光诊断和数值模型结合详细的传输和复杂的化学。研究了近熄灭管状火焰，以确定分子传输和化学机理对模型数据比较的影响。研究的重点是火焰半径与火焰厚度接近一致的高曲率火焰。为了改变路易斯数效应，研究了各种燃料。采用弧长延拓法准确预测消光条件。建立了管状火焰的全二维模型，验证了近消光自相似假设。最后，研究了预混管火焰与表面的相互作用，为微燃烧室的设计提供了参考。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，包括未被充分代表的少数民族，都参与了这项研究。精益燃料/空气预混在汽油燃料汽车和用于发电的以甲烷为燃料的燃气轮机中产生清洁和高效的燃烧。在实际装置中，稀薄预混火焰受到湍流的拉伸和弯曲影响，但对弯曲和弯曲影响的综合实验-数值研究很少。以往的研究大多集中在拉伸平面预混火焰上。曲率在预混火焰中很重要，因为微分扩散和曲率的结合可以极大地影响火焰的温度、气体成分和污染物的形成。曲率可以延缓或促进火焰的熄灭，弯曲的火焰可以在标准的低可燃性极限下存在；次极限。火焰有希望在高水平的效率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。教师将指导初高中学生学习工程。

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. .