Lyu Sijia, Tan Huanshu, Wakata Yuki, Yang Xianjun, Law Chung K, Lohse Detlef, Sun Chao
Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, International Joint Laboratory on Low Carbon Clean Energy Innovation, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China.
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544.
Proc Natl Acad Sci U S A. 2021 Jan 12;118(2). doi: 10.1073/pnas.2016107118.
The gasification of multicomponent fuel drops is relevant in various energy-related technologies. An interesting phenomenon associated with this process is the self-induced explosion of the drop, producing a multitude of smaller secondary droplets, which promotes overall fuel atomization and, consequently, improves the combustion efficiency and reduces emissions of liquid-fueled engines. Here, we study a unique explosive gasification process of a tricomponent droplet consisting of water, ethanol, and oil ("ouzo"), by high-speed monitoring of the entire gasification event taking place in the well-controlled, levitated Leidenfrost state over a superheated plate. It is observed that the preferential evaporation of the most volatile component, ethanol, triggers nucleation of the oil microdroplets/nanodroplets in the remaining drop, which, consequently, becomes an opaque oil-in-water microemulsion. The tiny oil droplets subsequently coalesce into a large one, which, in turn, wraps around the remnant water. Because of the encapsulating oil layer, the droplet can no longer produce enough vapor for its levitation, and, thus, falls and contacts the superheated surface. The direct thermal contact leads to vapor bubble formation inside the drop and consequently drop explosion in the final stage.
多组分燃料液滴的气化在各种能源相关技术中都很重要。与该过程相关的一个有趣现象是液滴的自诱导爆炸，产生大量较小的二次液滴，这促进了整体燃料雾化，从而提高了燃烧效率并减少了液体燃料发动机的排放。在此，我们通过对在过热板上处于良好控制的悬浮莱顿弗罗斯特状态下发生的整个气化过程进行高速监测，研究了由水、乙醇和油（“乌佐酒”）组成的三组分液滴的独特爆炸气化过程。观察到最易挥发成分乙醇的优先蒸发引发了剩余液滴中油微滴/纳米微滴的成核，结果，剩余液滴变成了不透明的水包油微乳液。微小的油滴随后聚结成一个大油滴，进而包裹住残余的水。由于有包裹性的油层，液滴不再能产生足够的蒸汽来维持悬浮，因此落下并接触到过热表面。直接的热接触导致液滴内部形成蒸汽泡，从而在最后阶段引发液滴爆炸。
