同结构活塞在FPE与CE两种工作模式下应力变形差异

为研究自由活塞发动机工作时活塞结构应力变形特点，采用有限元分析方法对比分析相同结构活塞在自由活塞发动机（free piston energy，FPE）与（crank engine，CE）两种工作模式下应力水平与变形状况差异性.结果表明，FPE活塞整体应力水平低于CE活塞，差异主要由机械载荷引起.上止点附近FPE缸内峰值压力较小，引起的活塞销座压应力被其较大的惯性力作用消减，导致该应力集中处应力值较低，约为CE活塞的72%.在热机载荷共同作用下两者活塞顶部变形相似，差异集中体现在裙部，FPE活塞所受缸压较小、加速度较大以及无侧向力的特点导致其裙部变形明显小于CE活塞，最大径向变形约为CE活塞的56%，更易满足各方面性能要求. 

Piston Stress and Deformation Comparison in FPE and CE Operating Mode

To study the stress and deformation characteristic of piston for free piston engine,a finite element method was used to analyze the differences of the piston stress and deformation between free piston engine (FPE) and crank engine (CE).Results show that:the stress level of FPE''s piston is lower than that of CE and the difference is mainly caused by mechanical load.As a result is of lower combustion pressure load and larger inertial load,the max stress of FPE''s piston is less,which is nearly 72% of CE''s piston.Under the thermo-mechanical coupling load,the difference of piston deformation between FPE and CE is small at the top and large at the skirt.The characteristics of the thermal load and the mechanical load of FPE piston result in smaller skirt deformation compared with CE piston,and the max FPE''s piston skirt radial deformation is nearly 56% of CE''s piston.