Experimental study on fusion and break-up motion after droplet collision

The interactions between droplets have an important influence on the atomization of liquid fuel,the combustion efficiency,and the reduction of particulate matter emissions for an engine.For this reason,this paper presents results from an experimental study on the coalescence and break-up of droplets after collision.According to the shape and parameters of the droplets at different times after the collision of the droplets was captured by a high speed camera,analysis was done for the following effects of droplet collisions:the collision-coalescence motion for the collision between the droplets,the change history of the dimensionless length-to-width ratio of the oscillation motion,the critical size ratio of the breakup motion,and the liquid physical properties of the particles.The results show that the droplets collide and exhibit two forms of coalescence oscillation and break-up:for oscillating motion,at higher droplet collision velocities and dimensionless size ratios,there will be a larger dimensionless length-to-width ratio for the droplet oscillation;for the break-up motion,at higher collision velocities,there will be lower dimensionless size ratios,and lower liquid surface tension,shorter times over which the droplet breaks,and facilitated droplet break-up.The research results presented here can be used for atomization in engine cylinder,increasing the gas/liquid contact area and enhancing the combustion efficiency of gas/liquid heat transfer to improve the combustion efficiency of the engine.

Hydrodynamics of passing-over motion during binary droplet collision in shear flow

A combined experimental and numerical study is undertaken to investigate the hydrodynamic characteristics of singlephase droplet collision in a shear flow. The passing-over motion of interactive droplets is observed, and the underlying hydrodynamic mechanisms are elucidated by the analysis of the motion trajectory, transient droplet deformation and detailed hydrodynamic information（e.g., pressure and flow fields）. The results indicate that the hydrodynamic interaction process under shear could be divided into three stages: approaching, colliding, and separating. With the increasing confinement, the interaction time for the passing-over process is shorter and the droplet processes one higher curvature tip and more stretched profile. Furthermore, the lateral separation ?;/R;exhibits larger decrease in the approaching stage and the thickness of the lubrication film is decreased during the interaction. As the initial lateral separation increases, the maximum trajectory shift by the collision interaction is getting smaller. During the collision between two droplets with different sizes, the amplitude of the deformation oscillation of the larger droplet is decreased by reducing the size ratio of the smaller droplet to the bigger one.