Surface Density Function and Its Evolution in Homogeneous and Inhomogeneous Mixture n -Heptane MILD Combustion
Surface Density Function and Its Evolution in Homogeneous and Inhomogeneous Mixture n -Heptane MILD Combustion
复制标题
均质和非均质混合物正庚烷轻度燃烧的表面密度函数及其演化
DOI：
10.1080/00102202.2023.2182197
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发表时间：
2023
影响因子：
1.9
通讯作者：
Abo-Amsha K
中科院分区：
文献类型：
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作者：
Abo-Amsha K
中度或强烈低氧稀释（MILD）燃烧是一种具有同时提高热效率和减少排放的潜力的燃烧技术。本文采用直接数值模拟（DNS）和简化化学反应机理，对废气再循环（EGR）型、均质和非均质混合物-庚烷混合物在温和燃烧条件下的反应标量梯度的平均行为及其演化规律进行了研究。对于均匀混合物的情况，这里考虑了两种氧浓度，即3.0%和4.5%体积比。在反应和传播火焰占主导地位的区域的SDF和位移速度的特性进行了分析，以说明燃烧模式对这些量的平均变化的影响。在湍流MILD燃烧情况下的SDF的平均值被发现是较小的相比，相应的层流火焰的情况下。此外，混合物的不均匀性对SDF变化的影响被认为是边际的参数在这里。结果发现，在相同的湍流条件下，增加稀释因子减少了火焰增厚的百分比相对于相应的层流火焰厚度。膨胀率的影响被认为是弱的，在所研究的情况下，由于预期的低热释放温和的条件下，导致弱的热膨胀效应。有效的火焰法向和切向应变率被认为是占主导地位的额外的火焰法向和切向应变率由于火焰传播，分别。有效火焰法向应变率具有正值的火焰，促进火焰增厚，并可以解释SDF值的减少，而有效火焰切向应变率是负的整个火焰，并表明火焰面积的分数减少，这可能是由于火焰表面的相互作用。反应占主导地位的区域引起的SDF在均匀混合物的情况下，在所有情况下的水平增加的SDF的水平相比，在传播火焰区域中的计算。
Moderate or intense low-oxygen dilution (MILD) combustion is a combustion technique with potential to simultaneously improve thermal efficiency and reduce emissions. This paper focuses on the mean behavior of the reactive scalar gradient characterized by the surface density function (SDF = magnitude of the reaction progress variable gradient) and its evolution for exhaust gas recirculation (EGR) type, homogeneous and inhomogeneous mixturen-heptane combustion under MILD conditions using Direct Numerical Simulations (DNS) with reduced chemical mechanism. Two oxygen concentrations have been considered here for the homogeneous mixture case, namely, 3.0% and 4.5% by volume. The characteristics of the SDF and displacement speed were also analyzed in the reaction and propagating-flame-dominated regions of the domain to illustrate the effect of combustion mode on the mean variations of these quantities. The mean values of the SDF in turbulent MILD combustion cases are found to be smaller compared to the corresponding laminar flame cases. Moreover, the effect of mixture inhomogeneity on the SDF variation is found to be marginal for the parameters considered here. It is found that increasing the dilution factor reduces the percentage of flame thickening with respect to the corresponding laminar flame thickness under identical turbulence conditions. The effects of dilatation rate are found to be weak in the studied cases due to the expected low heat release under MILD conditions which leads to weak thermal expansion effects. The effective flame normal and tangential strain rates are found to be dominated by the additional flame normal and tangential strain rates due to flame propagation, respectively. The effective flame normal strain rate has positive values across the flame which promotes flame thickening and could explain the decrease in the SDF values, while the effective flame tangential strain rate is negative throughout the flame and indicates a fractional reduction in flame area that could be attributed to flame surface interactions. The reaction-dominated regions give rise to reduced level of the SDF in the homogeneous mixture cases and increased level ofin all cases compared to those calculated in the propagating-flame region.