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A two-equation model for non-unity Lewis number differential diffusion in lean premixed laminar flames

机译:稀薄预混层流火焰中非单位Lewis数微分扩散的两方程模型

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Premixed flames are prone to develop thermo-diffusive instabilities when the diffusivity of the fuel is different from the rest of the mixture. Even when a uniform premixed composition is used, the local equivalence ratio across a flame front will not be constant. Therefore, a single quantity such as the progress variable is incapable of modeling accurately the combustion of non-unity Lewis number flames. In this work, a two-equation model is presented for the simulation of premixed laminar flames with non-unity Lewis number fuels. This model relies on the progress variable approach, which is suited for modeling premixed flames in which the fuel's Lewis number is near unity. An additional transport equation for a mixture fraction is derived for non-unity Lewis numbers. The model is verified to be consistent with simple laminar unstretched premixed flames. Hydrogen- and propane-air mixtures are used to demonstrate the model's ability to capture the respectively unstable and stable properties of each lean mixture. One dimensional spherical simulations reproduce the effects of flame stretch due to flow strain rate and flame curvature. Finally in two dimensions, the model captures the creation of cellular structures for negative Markstein length flames and the stable propagation of positive Markstein length flames.
机译:当燃料的扩散率与混合物的其余部分不同时,预混火焰容易产生热扩散不稳定性。即使使用均匀的预混合组合物,整个火焰前沿的局部当量比也不会恒定。因此,单个变量(例如进度变量)无法准确地模拟非统一Lewis数火焰的燃烧。在这项工作中,提出了一个两方程模型,用于模拟具有非统一路易斯数燃料的预混合层流火焰。该模型依赖于进度变量方法,该方法适用于对燃料的路易斯数接近于1的预混火焰进行建模。对于非单位路易斯数,导出了混合分数的附加输运方程。验证该模型与简单的层状未拉伸预混火焰一致。氢气和丙烷空气混合物用于证明模型捕获每种稀薄混合物各自不稳定和稳定特性的能力。一维球形模拟再现了由于流动应变率和火焰曲率引起的火焰拉伸的影响。最后在二维中,该模型捕获了负马克斯坦长度火焰的细胞结构的创建以及正马克斯坦长度火焰的稳定传播。

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