初始油温对油滴蒸发及穿透影响的数值研究

Numerical study on influences of initial temperature on single droplet’s evaporation and penetration characteristics

为研究初始油温对直接喷入横向气流过程中油滴蒸发与穿透深度的影响,建立了强迫对流影响下单个油滴非稳态和稳态蒸发速率与穿透轨迹计算模型,计算获得了初始油温对单个油滴油温、粒径、蒸发速率及蒸发时间的影响规律,以及不同油温下油滴的横向穿透轨迹。结果表明:初始油温从300 K增加到450 K,喷嘴出口喷射速度和供油压差随之增大,将导致喷嘴内燃油流动压力损失增大。环境气体温度900 K下,随着初始油温增高,油滴达到沸点的非稳定蒸发时长与总蒸发时长之比从37%减小到9%;初始粒径从40μm减小到22μm,油滴蒸发速率显著加快;相对蒸发速率从207 s^(-1)提高到4 556 s^(-1),达到相对蒸发速率峰值的时间明显提前。初始油温300K下油滴的轴向运动距离、横向穿透深度分别为206 mm和36 mm,初始油温450 K下则分别减小到36 mm和12mm,油滴的轴向运动距离和横向穿透深度均显著减小,从而导致燃烧室截面油气比分布不均。

In order to investigate influences of initial RP-3 temperature on the single droplet's evaporation and penetration characteristics in a crossflow,single droplet's evaporation and penetration model in a forced turbulent flow was established.Influences of RP-3 initial temperature on temperature,particle size,evaporation and penetration characteristics of a single droplet were calculated and traverse trajectory of droplet under different temperature was obtained.Results show that as RP-3 initial temperature increases from 300 to 450 K,the jet velocity and the pressure increases,leading to larger pressure loss of the nozzle.For a fixed inlet air temperature of 900 K,the ratio of RP-3 unsteady evaporation duration and total evaporation duration decreases from 37%to 9%as RP-3 initial temperature increases,and initial droplet diameter decreases from 40 to 22μm.Thus droplet evaporation process is significantly accelerated.Besides,the initial relative evaporation rate increases from 207 to 4556 s^(-1),and the time to reach the peak of the relative evaporation rate gets significantly earlier.Furthermore,for an initial oil temperature of 300 K,the axial distance and transverse penetration deepth are 206 mm and 36 mm respectively.But with a higher oil temperature of 450 K,it decreases to 36 mm and 12 mm respectively.The axial distances and transverse penetration deepthare significantly reduced,which leads to an inhomogeneous oil distribution.