The Dynamism of Combustion and Flame of Three-Dimensionally Dispersed Fuel System under Microgravity Conditions

研究了三维分散燃料系统燃料液滴团簇从蒸发到自燃的连续非定常过程，并分析了主要影响因素对该过程的影响。本研究以实验为主，利用微重力环境降低自然对流对注意力现象的影响，使注意力现象复杂化。实验对象还包括液滴阵列和单个液滴。利用LIF法进行非侵入式测量，并对火焰中的自由基种类进行了数值模拟。实验对象为约50个液滴的液滴簇、约10个液滴的液滴簇、约10个液滴的液滴阵列和单个液滴。对于单液滴，重点研究了燃料和环境气体性质对其燃烧特性的影响，并阐明了常规微重力实验中的燃烧特性。我们还在正常重力条件下的弱流动中进行了液滴实验，自然对流的影响相对减少，并阐明了液滴火焰内部煤烟和羟基自由基的分布。以气体速度和液滴直径为变量，绘制了火焰形状和熄灭的模态图。模拟得到了自由基分布的结果，并建立了详细的反应模型，并证实了环境湿度对自由基分布的影响。研究了液滴间距、燃料性质和环境气体速度对液滴阵列火焰传播速度的影响，以及液滴间距对微重力条件下液滴团的非定常蒸发过程、自燃延迟时间和火焰生长行为的影响。

The objective of the present research was to observe the successive unsteady processes from evaporation to combustion after autoignition of fuel droplet clusters, which were the three-dimensionally dispersed fuel systems, and to elucidate the effects of primary factors on the processes. Experiments were mainly conducted in the present study, and microgravity environments were utilized in the experiments for reducing the effects of natural convection, which complicated the phenomena of attention. Droplet arrays and single droplets were also included as the experimental objects. Non-intrusive measurement with LIF method and numerical simulation of radical species in the flames were conducted for deeper understanding.The experimental objects were the droplet clusters with about 50 droplets, those with about 10 droplets, the droplet arrays with about 10 droplets and the single droplets. For the single droplets, we focused our attention on the effects of properties of the fuel and the ambient gas, and elucidated the conventional combustion characteristics in the microgravity experiments. We also conducted the droplet experiments in weak flows under the normal gravity condition, where the effects of natural convection were relatively reduced, and elucidated the distributions of soot and hydroxyl radical inside the droplet flame. The mode map of the flame shape and extinction was made with the gas velocity and the droplet diameter as the variables. The results on the radical distribution were reproduced in the simulation, which included a detailed reaction model, and the obtained effects of the ambient gas humidity were confirmed. Also elucidated were the effects of the droplet spacing, the fuel properties and the ambient gas velocity on the flame spread speed of the droplet array, and the droplet spacing effects on the unsteady evaporation process, on the delay time of autoignition and on the behavior of the flame growth of the droplet clusters in microgravity.