Fluid dynamic and autoignition characteristics of early fuel sprays using hybrid atomization LES
Fluid dynamic and autoignition characteristics of early fuel sprays using hybrid atomization LES
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DOI：
10.1016/j.combustflame.2019.02.009
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发表时间：
2019-05
影响因子：
4.4
通讯作者：
J. Shinjo;A. Umemura
中科院分区：
文献类型：
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作者：
J. Shinjo;A. Umemura
早期的燃油喷雾发展和随后的自燃进行了研究，使用我们的湍流雾化模型，使物理封闭的初级雾化建模。由于其建模方法，无需参数调整或调整即可模拟湍流喷雾。由于湍流雾化，在注入的液芯上形成致密的液滴层。随着蒸发，该区域具有三层结构，其由具有许多液滴的内层、蒸发层和暴露于热空气的外层组成。随着燃烧，在外层产生热点，而内层太冷，阻碍热气体渗透到内部。群燃烧数表明这是鞘蒸发/燃烧模式，并且其结构保持到液芯长度。液芯变薄由雾化特性决定，并且在外部气体温度高且因此运动粘度也高的蒸发/反应条件下，流动运动较大，并且芯受到该运动的不稳定影响。由于这一点，瑞利-泰勒（RT）原子化模式被进一步激发和核心破碎发生相对较快。研究还发现，非定常的芯头摆动运动会导致液滴和蒸汽的不均匀分布。由于这种不均匀性，外层中的初始自燃不会均匀地发生。核心破碎后，液滴层在前部区域卷起，群燃烧数降低，出现外部群燃烧现象。与全局化学相比，多步化学改善了点火延迟估计，但喷雾动力学主要由上述流体动力学效应决定。因此，本研究表明，流体动力学的准确模拟能力，即初级雾化和早期喷雾发展，在预测喷雾燃烧行为是重要的。
Early fuel spray development and subsequent autoignition are investigated using our turbulent atomization model that has enabled physically-closed primary atomization modeling. Thanks to its modeling methodology, no parameter tuning or adjustment is needed to simulate a turbulent spray. Due to turbulent atomization, a dense droplet layer is formed over the injected liquid core. With evaporation, this region has a triple layer structure, which is composed of the inner layer with many droplets, the vaporization layer and the outer layer exposed to the hot air. With combustion, hot spots are generated in the outer layer, while the inner layer is too cold and hinders the hot gas to penetrate inside. The group combustion number indicates that this is sheath evaporation/combustion mode and its structure is preserved down to the liquid core length. The liquid core thinning is determined by atomization characteristics and under evaporative/reactive conditions where the outer gas temperature is high and thus the kinematic viscosity is also high, the flow motion is larger and the core is unsteadily affected by this motion. Due to this, the Rayleigh–Taylor (RT) atomization mode is further excited and core breakup occurs relatively faster. It is also observed that the unsteady core head flapping motion leads to non-uniform distributions of droplets and vapor. Due to this non-uniformity, the initial autoignition in the outer layer does not occur uniformly. After core breakup, the droplet layer rolls up in the front region and the group combustion number becomes lower, where external group combustion behavior is observed. Multistep chemistry improves the ignition delay estimation compared with the global chemistry, but the spray dynamics is mostly determined by the above fluid dynamic effects. Therefore, the present study indicates that the accurate simulation capability of fluid dynamics, i.e. primary atomization and early spray development, is important in predicting spray combustion behavior.