A Study of Initial Process of Liquid Atomization by Using a Semiconductor Laser 2-Focus Velocimeter

为了研究液体雾化的初始过程，需要较小的探针体积，因为每个液滴都应该在高密度液滴中进行识别。激光双焦点测速仪L2F天生就满足了这一要求，因为L2F具有高的光信噪比和可减小的探头体积。采用半导体激光器作为光源，带微型探针的L2F测量了液滴的分解过程。通过飞行时间和散射时间在探针体积内同时测量液滴的速度和大小。对新研制的L2F的测量精度进行了检验。结果表明，即使液滴速度增加30倍，加湿器所产生的水滴的大小也被评价为恒定的。以柴油喷入大气为实验对象，对喷嘴口附近液滴解体过程即液体雾化初始过程进行了测量。结果表明，大滴、高速滴在喷雾芯内崩解。用L2F测量结果验证了液滴崩解模型之一的增强TAB模型。结果表明，在适当估计液滴崩解后尺寸的情况下，增强TAB模型可以模拟雾滴在喷雾芯内的崩解过程。由于所开发的L2F可以测量液滴的速度和大小，当液滴的间距大于两个焦点之间的距离时，L2F不能测量液柱。然而，当L2F得到无效数据时，表明存在液柱。用L2F测量液柱是一个未来的课题。

In order to investigate the initial process of liquid atomization, a smaller probe volume is desired, since each droplet should be identified in high number density droplets. A laser 2-focus velocimeter, L2F, inherently satisfies this requirement, because L2F has a high optical signal to noise ratio and the probe volume is reducible. A L2F, which uses a semiconductor laser as the light source and has a micro-scale probe, was used for the measurement of droplets in a disintegration process. The velocity and size of droplets were measured simultaneously by time-of-flight and time-of-scattering in the probe volume.1.The measurement accuracy of the L2F developed newly was examined. It is shown that the size of water droplets generated by a humidifier was evaluated as a constant even if the droplet velocity increased 30 times.2.The measurement of droplet disintegration process near the nozzle orifice, i.e., the initial process of liquid atomization, was conducted in a diesel fuel spray injected into the atmosphere. It is shown that large and high velocity droplets disintegrate in the spray core.3.Enhanced TAB model, one of droplet disintegration model, was verified by the L2F measurement result. It is shown that the enhanced TAB model can simulate the droplet disintegration process in the spray core if the droplet size after disintegration is suitably estimated.As the developed L2F can measure the velocity and size of droplets when a droplet's interval is longer than the distance between two foci, L2F can not measure a liquid column. However, when invalid data is obtained by the L2F, existence of a liquid column is suggested. The measurement of a liquid column by the L2F is a future subject.