曲轴箱内机油液滴撞壁飞溅的影响因素

Influencing Factors of Splashing Caused by Engine Oil Droplets Impacting on Wall in the Crankcase

在发动机曲轴箱内,机油液滴撞击固体表面后的飞溅现象对机油油雾的形成有重大影响.结合流体体积函数(VOF)和壁面润湿模型,运用局部网格瞬时加密技术,建立了机油液滴冲击润湿壁面的计算模型,并通过试验验证了模型的可靠性.结果表明:机油液滴的黏度、表面张力以及油膜厚度等因素均会对撞壁后的飞溅过程产生显著影响.黏度越大,飞溅产生的二次液滴就越少,但黏度对二次液滴群的索特平均直径(SMD)并没有显著影响;机油表面张力越大,产生的二次液滴就越少,且二次液滴群的SMD也会明显变大;壁面润湿的前提下,壁面油膜越厚,撞壁飞溅产生的二次液滴就越多,平均尺寸也越大.

The splashing caused by the engine oil droplets impacting on the crankcase wail has a significant impact on the formation of oil mist in the engine. With the wall wetting model and the instantaneous local mesh encryption technology, a volume of fluid （VOF） model for oil droplet impinging wetted wall was established. The reliability of the model was verified by experimental results as well. The results show that the splashing process after impinging is affected remarkably by oil droplet viscosity, sttrface tension and the thickness of oil film. Increasing the viscosity can reduce the total mass of secondary droplets, but Sauter mean diameter （SMD） of the secondary droplets is not affected significantly. Raising the surface tension can inhibit the generation of the secondary droplets and make their average size increase obviously. With the oil film thickening, the wall wetted by oil can generate more secondary droplets with bigger average sizes.