液滴间相互碰撞融合与破碎的实验研究

Experimental study on collision coalescence and breakage between droplets

液滴间的相互碰撞对发动机液体燃料雾化、燃烧效率及颗粒物排放的减少均有重要影响;为了探究液滴间相互碰撞后的液滴融合与破碎过程,采用高速摄影技术对液滴间相互碰撞的融合过程、融合振荡无量纲宽长比变化历程、破碎过程以及液体物性参数对碰撞破碎的影响进行了分析。结果表明,液滴间相互碰撞后主要呈现融合振荡与破碎两种运动形态;对融合振荡形态而言,两液滴间的碰撞速度及初始无量纲尺寸比越大,融合后液滴振荡的宽长比的最大值越大;对破碎形态而言,两液滴间的碰撞速度越大、初始无量纲尺寸比越小以及大液滴的表面张力越小,液滴发生破碎的时刻越小。研究结果可以为改善发动机缸内雾化,增大气/液间的接触面积,强化气/液间传热传质提供理论依据。

Collision between droplets is important on engine liquid fuel atomization, combustion efficiency and reduction of particulate emissions. In order to explore droplet coalesence and breakage processes after collision, high-speed photography was used to study dimensionless aspect ratio change of coalescence oscillation processes, breaking processes and liquid properties. The effects of collisional breakage were analyzed. The results show that oscillating and breaking motion are the main form after collision. For oscillating motion, larger collision speeds and dimensionless size ratios lead to larger aspect ratios of droplet oscillation. For breaking motion, larger collision speed results in smaller dimensionless size ratio, and smaller surface tension of the liquid leads to smaller break time with easier droplet breakage. The results can be used for studying atomization in engine cylinder, and provide guidance for increasing the contact area between gas/liquid, and enhancing the combustion efficiency of gas/liquid heat transfer to improve combustion efficiency of engines.