空化对燃油喷嘴雾化的影响

Effects of Cavitation in Nozzle on Spray

关键词:  空化  圆形喷嘴  雾化  喷嘴直径  喷嘴长径比 

Key words:  Cavitation  Round nozzle  Atomization  Diameter of nozzle  Length to diameter of nozzle

摘要:

燃油喷嘴内的液体流动在一定条件下会形成空化,进而影响喷嘴的雾化效果。应用高速摄像仪对圆形喷嘴内的空化以及喷口外的雾化进行了实验研究。实验所用喷嘴直径包括0.5mm,1.0mm,1.5mm和2.0mm,其中直径为1.5mm的喷嘴的长径比从2变化到9,实验工质为纯净水。实验发现,喷嘴内空化的形成是动态的,空化长度出现高频低幅脉动。对于喷嘴的收缩类型研究发现,急收型相比渐收型更易形成空化,并有增强雾化的效果。长径比相同的喷嘴,直径越大,达到超空化的喷射压力越大,雾化锥角也越大；直径相同的喷嘴,随长径比的增加,达到超空化的空化数逐渐减小,但射流的喷雾锥角没有明显的变化趋势,均在10°到20°之间。对比破碎模式规律,除了0.5mm的喷嘴外,所有喷嘴达到超空化后均为雾化模式。 

Abstract:

Experiments were conducted to investigate the cavitation in the round nozzles and its influence on atomization. The liquid flow in the nozzle will induce cavitation under certain condition. It has an important influence on spray. The high-speed camera was used to observe the cavitation and spray angle. The diameters of nozzles used in the experiments were 0.5mm, 1.0mm, 1.5mm, 2.0mm,respectively. Especially for the nozzle with 1.5mm diameter, the length to diameter ratio was designed to vary from 2to 9, and the tested liquid was purified water. Present results indicate that the formation of cavitation in nozzles is dynamical and the cavitation length is pulsating with high frequency and low amplitude. With the increase of the diameter of the nozzle, the injection pressure for the supercavitation condition is increased and the spray angle is also increased. The supercavitation number is decreased with the increase of the length to diameter of the nozzle but the spray angle within the range of 10° and 20° does not present a significant change. The cavitation which enhances the atomization is easier to happen in nozzle with sharp inlet than with conical inlet. The breakup mode comes to atomization for all nozzles in the supercavitation condition, except for 0.5mm.