二冲程液压自由活塞发动机换气过程影响因素的仿真研究

Simulation of Factors Influencing Gas Exchange Process of Two-Stroke Hydraulic Free Piston Engine

利用CONVERGE软件建立了二冲程液压自由活塞发动机换气过程的三维计算流体动力学(computational fluid dynamics,CFD)仿真模型,并且基于液压自由活塞发动机的独特结构,研究了气口比时面值、扫气箱压缩比、活塞顶倾角和活塞杆直径对换气过程的影响。结果表明:在未发生废气倒流时,扫气效率主要与扫气比时面值有关,增大扫气比时面值有利于提高扫气效率;捕获率主要与排气比时面值有关,减小排气比时面值有利于增大捕获率;提高扫气箱压缩比有利于提高扫气效率,扫气箱压缩比从1.2增加到2.1,扫气效率提升9.8%;适当增大活塞顶倾角有利于扫气效率和捕获率的提高;减小活塞杆直径有利于提升扫气效率,但同时会导致捕获率下降。

A three-dimensional computational fluid dynamics(CFD)simulation model of two-stroke hydraulic free-piston engine(HFPE)was built by the CONVERGE.The effects of specific time-area value,compression ratio of scavenge case,piston top angle,and piston rod diameter on scavenging process were studied based on the unique structure of the HFPE.The results show that the scavenging efficiency is mainly affected by the specific scavenging time-area value when there is no backflow of exhaust gas,and the improvement of the later is beneficial to the former.The capture ratio is mainly affected by the specific timearea value of exhaust,and the reduction in the later can increase the former.Increasing the scavenge case compression ratio from 1.2 to 2.1 can promote the scavenging efficiency by 9.8%.The appropriate increase of the piston top angle is beneficial to the improvement of the scavenging efficiency and capture ratio.Decreasing the diameter of the piston rod diameter can increase the scavenging efficiency,but it will reduce the capture ratio.