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Effects of differential diffusion on nonpremixed-flame temperature
Proceedings of the Combustion Institute ( IF 3.4 ) Pub Date : 2018-10-10 , DOI: 10.1016/j.proci.2018.06.176
A. Almagro , O. Flores , M. Vera , A. Liñán , A.L. Sánchez , F.A. Williams

This numerical and analytical study investigates effects of differential diffusion on nonpremixed-flame temperatures. To focus more directly on transport effects the work considers a single irreversible reaction with an infinitely fast rate, with Schab–Zel’dovich coupling functions introduced to write the conservation equations of energy and reactants in a chemistry-free form accounting for non-unity values of the fuel Lewis number LF. Different flow configurations of increasing complexity are analyzed, beginning with canonical flamelet models that are reducible to ordinary differential equations, for which the variation of the flame temperature with fuel-feed dilution and LF is quantified, revealing larger departures from adiabatic values in dilute configurations with oxidizer-to-fuel stoichiometric ratios S of order unity. Marble’s problem of an unsteady flame wrapped by a line vortex is considered next, with specific attention given to large-Peclet-number solutions. Unexpected effects of differential diffusion are encountered for S < 1 near the vortex core, including superadiabatic/subadibatic flame temperatures occurring for values of LF larger/smaller than unity as well as temperature profiles peaking on the oxidizer side of the flame. Direct numerical simulations of diffusion flames in a temporal turbulent mixing layer are used to further investigate these unexpected differential–diffusion effects. The results, confirming and extending previous findings, underscore the nontrivial role of differential diffusion in nonpremixed–combustion systems.



中文翻译:

差异扩散对非预混火焰温度的影响

这项数值和分析研究调查了微分扩散对非预混火焰温度的影响。为了更直接地关注传输效应,该工作考虑了无限快的单个不可逆反应,并引入了Schab–Zel'dovich耦合函数,以无化学形式写出了能量和反应物的守恒方程,并计算了非统一性值。燃料刘易斯数大号F。首先从可简化为常微分方程的规范小火焰模型开始,分析复杂度不断提高的不同流动配置,对于这些模型,火焰温度随燃料进料稀释和温度的变化而变化。大号F量化,揭示了与氧化剂/燃料化学计量比S为1的稀薄配置中绝热值的较大差异。接下来考虑由线涡旋涡包裹的不稳定火焰的大理石问题,并特别关注大佩克雷特数解。 在涡旋核心附近,S <1遇到差异扩散的意外影响,包括超绝热/亚绝热火焰温度出现在大号F大于/小于单位以及温度分布在火焰的氧化剂侧达到峰值。在时间湍流混合层中扩散火焰的直接数值模拟被用来进一步研究这些意想不到的微分扩散效应。该结果证实并扩展了先前的发现,强调了在非预混燃烧系统中微分扩散的重要作用。

更新日期:2018-10-10
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