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Dependence of kinetic sensitivity direction in premixed flames
Combustion and Flame ( IF 4.4 ) Pub Date : 2020-10-01 , DOI: 10.1016/j.combustflame.2020.06.027
Weiqi Ji , Tianwei Yang , Zhuyin Ren , Sili Deng

Extinction strain rate (ESR) and laminar flame speed (LFS) are fundamental properties of a fuel/air mixture that are often utilized as scaling parameters in turbulent combustion. While LFS at atmospheric and elevated pressures are extensively investigated, experimental measurements of ESR with counterflow premixed flames are very limited for flame instability often occurs near extinction, especially at high pressures. Due to the scarcity of ESR measurements, most combustion kinetic models are mainly validated and optimized against LFS. However, it is questionable whether the controlling reactions are the same for ESR and LFS such that those models are also valid for predicting ESR. This work quantifies the kinetic similarities between ESR and LFS by analyzing their kinetic sensitivity directions. The direction is represented by a unit vector composed of the normalized sensitivity of ESR or LFS to the rate constant for each elemental reaction. Consequently, the similarity between the two directions is measured by the inner product of the corresponding unit vectors. The sensitivity directions of ESR and LFS are found parallel for various fuels, equivalence ratios, and pressures. Furthermore, sensitivity directions at various strain rates are also similar for the maximum temperature, local temperature at various locations in the flame coordinate, and ESR in counterflow premixed flames. These findings suggest that LFS and ESR are similarly effective as the target for constraining and optimizing rate constants in kinetic models. In addition, the independence of the sensitivity directions on the strain rate also enables us to perform uncertainty quantification for turbulent flames with a wide range of strain rates based on the kinetic sensitivity of ESR and LFS.

中文翻译:

预混火焰中动力学灵敏度方向的依赖性

消光应变率 (ESR) 和层流火焰速度 (LFS) 是燃料/空气混合物的基本特性,通常用作湍流燃烧中的标度参数。虽然对大气压和高压下的 LFS 进行了广泛的研究,但使用逆流预混火焰的 ESR 的实验测量非常有限,因为火焰不稳定经常发生在接近熄灭的地方,尤其是在高压下。由于 ESR 测量的稀缺性,大多数燃烧动力学模型主要针对 LFS 进行验证和优化。然而,ESR 和 LFS 的控制反应是否相同,以至于这些模型对于预测 ESR 也是有效的,这是值得怀疑的。这项工作通过分析 ESR 和 LFS 的动力学敏感性方向来量化它们之间的动力学相似性。方向由单位向量表示,该单位向量由 ESR 或 LFS 对每个元素反应的速率常数的归一化灵敏度组成。因此,两个方向之间的相似性由相应单位向量的内积来衡量。发现 ESR 和 LFS 的灵敏度方向对于各种燃料、当量比和压力是平行的。此外,对于最高温度、火焰坐标中不同位置的局部温度以及逆流预混火焰中的 ESR,不同应变率下的灵敏度方向也相似。这些发现表明,LFS 和 ESR 作为约束和优化动力学模型中速率常数的目标同样有效。此外,
更新日期:2020-10-01
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