液压自由活塞发动机性能模拟的参数化研究

Performance Simulation for Parametric Study of a Hydraulic Free Piston Engine

液压自由活塞发动机的工作过程是在多过程相互耦合作用下进行,活塞动力学与燃烧、扫气、泵油各过程紧密结合。基于Aemsim建立了一维仿真模型,在分析运动特性和热力学特性的基础上,研究了关键性结构和控制参数对发动机性能的影响。仿真结果表明:由于没有机械约束,自由活塞发动机的活塞行程规律与曲柄发动机存在显著的差异;活塞质量是影响热效率和工作频率的最重要因素,效率和频率随活塞质量的变化趋势相反;由于上止点附近停留时间短和工作行程活塞快速下行,在相同结构和运转条件下最优效率略低于曲柄连杆发动机;放热率和活塞惯量的综合作用决定其热效率,压缩比和喷油时刻对效率的影响不如曲柄发动机显著;活塞行程规律可变,通过行程控制可以显著缩短压缩行程占据的时间。

predict the A one-dimensional simulation model of hydraulic free piston engine is established based on Amesim to dynamic and thermodynamic characteristics of this new engine prototype under direct coupling processes of piston dynamics, scavenge, combustion and hydraulic pumping, and the effects of key parameters of structure and control on engine performance are revealed. The simulation results show that there are significant differences in the dynamic characteristics between free piston and crank engine. Like a spring-mass system, piston mass is the most important parameter that defines the frequency and the efficiency and operating frequency change in the opposite trend with the mass. Due to rapid decline of piston after top dead center, the optimum efficiency is slightly lower than the crank engine under the same operating condition. Combined effect of piston inertia and heat release determines the energy conversion, resulting in less sensitivity of compression ratio and injection timing on thermal efficiency as crank engine. The piston motion is variable without mechanical constraints, the time taken by compression stroke can be significantly reduced through stroke control.