液态LNG喷雾过程闪急沸腾条件数值模拟研究

Numerical Simulation Research on Conditions of Liquid LNG Flash Boiling Spray

由于闪急沸腾喷雾可以改善燃油雾化质量,对缸内混合气的形成十分有利,所以研究液态LNG的闪急沸腾喷雾具有非常重要的意义。文章首先解析了纯液态LNG在喷嘴内部的流动过程,利用其计算结果作为LNG喷雾计算的初始条件和边界条件,在此基础上,使用AVL Fire软件激活了初始破碎模型及Flash Boiling模型,对纯液态LNG闪急沸腾喷雾过程进行了数值模拟计算,研究了喷雾发展的过程,并确定了LNG液态喷射发生闪急沸腾现象的条件,数值计算结果与文献结果吻合较好。计算研究表明,当环境压力处于[0.1 MPa,4.59 MPa]区间时,只要环境压力小于液态LNG饱和蒸气压,均可发生闪急沸腾现象;当环境压力大于4.59 MPa时,不论液态LNG温度如何变化,都不能发生闪急沸腾现象;LNG闪急沸腾喷雾形状始终保持为类圆锥体,但并不完全对称,在发展过程中,液滴直径迅速减小,喷雾前端会形成涡旋结构,随后,该结构破碎、消失。

The quality of fuel atomization can be improved by flash boiling spray, which is very beneficial to the formation of air-fuel mixture in the cylinder, so it is very important to study the flash boiling spray of LNG. First of all, the flow process of LNG inside the nozzle is analyzed, and the calculated results are taken as initial and boundary conditions of LNG spray calculation. On this basis, a numerical simulation model of pure liquid LNG flash boiling spray is created to investigate the development of the spray process, and the conditions of LNG liquid injection occur flash boiling phenomenon are determined. All results obtained by the numerical model of LNG flash boiling spray are consistent with the exact solutions given in the literatures. The results show that, when the ambient pressure is in the range of [0.1 MPa, 4.59 MPa], flash boiling phenomenon occurs,as long as the ambient pressure is lower than the saturation vapor pressure of the liquid LNG; when the ambient pressure is more than 4.59 MPa, no matter how the temperature of liquid LNG changes, flash boiling phenomenon never occurs. It is also found that the shape of LNG flash boiling spray remains incompletely symmetrical cone, and the droplet diameter decreases rapidly in the process of development. A vortex structure in spray tip is formed, and then the structure is broken and disappeared.