DNS of MILD combustion with mixture fraction variations
DNS of MILD combustion with mixture fraction variations
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DOI：
10.1016/j.combustflame.2017.10.030
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发表时间：
2018-03-01
影响因子：
4.4
通讯作者：
Minamoto, Yuki
中科院分区：
文献类型：
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作者：
Nguyen Anh Khoa Doan;Swaminathan, Nedunchezhian;Minamoto, Yuki
本文对立方体区域内的中、强低氧稀释燃烧进行了直接数值模拟。计算域在一个方向上指定流入和流出边界条件，在其他两个方向上指定周期性条件。流入的混合物在预处理步骤中仔细构造，并且具有空间变化的混合物分数和反应进程变量场。因此，对于给定的混合物分数值，该混合物包括一系列热化学状态。燃烧动力学建模使用58步骨架机制，包括发光物种，OH*，甲烷-空气燃烧。物理和混合分数空间中的反应区结构的研究表明，存在点火前锋，贫油和丰富的预混火焰和非预混燃烧。这三种燃烧模式没有观察到典型的三重火焰结构，这是由于时空变化的混合物分数场进行湍流混合和反应。分析火焰指数及其pdf，以估计这些燃烧模式对总热释放速率的贡献。稀薄预混模式被观察到是相当占主导地位的和非预混模式的贡献从约11%增加到20%时，在流入的混合物中的平均氧气摩尔分数从约2.7%降低到1.6%。此外，非预混的贡献增加，如果一个减少的混合分数场的积分长度尺度。所有这些结果和观察都是在物理基础上解释的。(C)2017作者爱思唯尔公司出版
Direct numerical simulations of Moderate or Intense Low-oxygen Dilution combustion inside a cubical domain are performed. The computational domain is specified with inflow and outflow boundary conditions in one direction and periodic conditions in the other two directions. The inflowing mixture is constructed carefully in a preprocessing step and has spatially varying mixture fraction and reaction progress variable fields. Thus, this mixture includes a range of thermo-chemical states for a given mixture fraction value. The combustion kinetics is modelled using a 58-step skeletal mechanism including a chemiluminescent species, OH*, for methane-air combustion. The study of reaction zone structures in the physical and mixture fraction spaces shows the presence of ignition fronts, lean and rich premixed flames and non-premixed combustion. These three modes of combustion are observed without the typical triple-flame structure and this results from the spatio-temporally varying mixture fraction field undergoing turbulent mixing and reaction. The flame index and its pdf are analysed to estimate the fractional contributions from these combustion modes to the total heat release rate. The lean premixed mode is observed to be quite dominant and contribution of non-premixed mode increased from about 11% to 20% when the mean oxygen mole fraction in the inflowing mixture is reduced from about 2.7% to 1.6%. Also, the non-premixed contribution increases if one decreases the integral length scale of the mixture fraction field. All of these results and observations are explained on physical basis. (C) 2017 The Authors. Published by Elsevier Inc.