对置式液压自由活塞发动机扫气过程的仿真

Simulation and Optimization of the Scavenging Process of an Opposed-Piston Hydraulic Free Piston Engine

根据所开发的对置式液压自由活塞发动机样机的基本参数,基于AVL FIRE平台建立了缸内流场的三维仿真模型.分析了扫气口几何参数、活塞下止点停留时间对扫气过程的影响,探讨了利用扫气口几何参数实现缸内混合气分层的方法.结果表明:扫气口径向夹角为5°时,扫气效率和扫气捕获率都达到最大值;随着活塞下止点停留时间的加长,扫气效率呈现先提高再稳定的过程,扫气捕获率则随停留时间的加长而单调下降;采用较大的扫气口径向夹角,可以在压缩上止点附近,实现缸内轴心处废气浓度高、外围废气浓度低的分层分布.

A three-dimensional （3D） computational fluid dynamics （CFD） model was established with AVL FIRE on the basis of the opposed-piston hydraulic free piston engine. Effect of geometric parameters and staying period at bot- tom dead center （BDC） on the scavenging process was analyzed, and discussed the method to achieve stratified charge using the scavenging port. Simulation results showed scavenging efficiency and trapping efficiency give their highest values when intake radial angle is 5~. Scavenging efficiency increases and trapping efficiency decreases when staying period at BDC is increased. Larger intake port radial angle can realize the stratified charge where burnt gas was con- centrated around the cylinder axis.