燃油喷雾撞壁与油膜蒸发特性研究

Study on the Characteristics of Fuel Spray Impingement and Film Evaporation

构建了一维非稳态燃油喷雾撞壁模型,综合考虑了液滴蒸发、油膜铺展和油膜温度等影响因素.针对燃油喷雾撞壁过程进行分阶段建模:在自由贯穿阶段,基于射流喷雾液相贯穿距离预测模型和液滴蒸发模型描述自由贯穿阶段,并确定喷雾撞壁时刻.在撞壁阶段,燃油喷雾被离散为液滴微元撞击壁面的过程.耦合自由液滴蒸发模型、油膜表面温度模型和油膜蒸发模型,以油膜铺展半径为特征参数构建了附壁油膜在撞壁阶段、附壁油膜铺展阶段和油膜蒸发阶段的一维非稳态归一化模型.讨论了环境温度、压力、喷油压力和初始油膜厚度对喷雾内液滴直径、液滴蒸发质量和油膜蒸发速率的影响.结果表明:阶段化、离散化的一维非稳态撞壁喷雾模型能够准确地预测在宽范围环境温度工况下的喷雾贯穿、近壁面铺展、燃油附壁以及蒸发过程.提高环境温度、降低环境压力能够提高附壁油膜表面最高温度,增大油膜的蒸发速率.

A one-dimensional non-stationary spray impinging model was constructed.Several key factors like droplet evaporation,fuel film spreading and fuel film surface temperature were considered in this model.For fuel spray impingement,staged modeling was used.In the free penetration stage,the spray was described using a liquid phase penetration length prediction model and droplet evaporation model,then the impingement moment was determined.In the spray impingement stage,the spray was simplified to the spray impingement process of the microelement droplets.Coupling the droplet evaporation model,the fuel film surface temperature model and the fuel film evaporation model,a one-dimensional unsteady normalized model was constructed to predict the fuel film across the spray impingement stage,the fuel film spreading stage and the fuel film evaporation stage with spreading radius of the fuel film as the characteristic parameter.The results show that the staged and discretized onedimensional unsteady impingement spray model can accurately predict the spray penetration,near-wall spreading,fuel adhesion and evaporation processes under a wide range of ambient temperatures.It is found that increasing the ambient temperature and decreasing the ambient pressure can increase the maximum temperature of the fuel film surface and accelerate the evaporation rate of the fuel film.