This study presents an experimental investigation of a free piston expander-linear generator (FPE-LG) used for organic Rankine cycle (ORC) waste heat recovery system. A FPE-LG test rig using compressed air as working fluid is established. The motion characteristics, dynamic characteristics and the indicated efficiency of FPE-LG are analyzed. The motion characteristics and power output performance for different valve timings are studied. The degree of symmetry is defined to evaluate the asymmetry motion characteristics of the free piston assembly. The coefficient of cycle-to-cycle variation (COV) is presented to evaluate the cycle-to-cycle variation characteristics of the FPE-LG. Experimental results show that the free piston assembly displacement profile is similar to a sinusoidal wave and the free piston assembly can operate at high and relatively constant speed at the middle portion of the stroke. The maximum power output of 19 W can be achieved when the intake pressure is 2.0 bar and the operation frequency is 2.5 Hz. The valve timing and intake pressure demonstrate a significant influence on the asymmetric motion and the power output performance of the FPE-LG. The indicated efficiency of the FPE (left cylinder) decreases with the increase in the intake pressure. The maximum indicated efficiency reaches 92.8% when the intake pressure is 1.4 bar and the operation frequency is 2.0 Hz. The indicated efficiency firstly increases and then decreases with the increase in the operation frequency. The COV of the FPE-LG decreases with increasing the intake pressure. The motion stability of FPE-LG improves with the increase in the intake pressure. Valve timing and valve train should be optimized in the near future.

这项研究提出了一种用于有机朗肯循环（ORC）废热回收系统的自由活塞膨胀机-线性发生器（FPE-LG）的实验研究。建立了使用压缩空气作为工作流体的FPE-LG试验台。分析了FPE-LG的运动特性，动态特性和指示效率。研究了不同气门正时的运动特性和功率输出性能。定义对称度以评估自由活塞组件的不对称运动特性。给出了周期间变化系数（COV）以评估FPE-LG的周期间变化特性。实验结果表明，自由活塞组件的位移曲线类似于正弦波，并且自由活塞组件可以在冲程的中间部分以较高且相对恒定的速度运行。当进气压力为2.0 bar，工作频率为2.5 Hz时，可以实现19 W的最大功率输出。气门正时和进气压力显示出对FPE-LG的不对称运动和功率输出性能的重大影响。FPE（左气缸）的指示效率随进气压力的增加而降低。当进气压力为1.4 bar，工作频率为2.0 Hz时，最大指示效率达到92.8％。指示效率随着工作频率的增加先上升然后下降。FPE-LG的COV随着进气压力的增加而降低。FPE-LG的运动稳定性随进气压力的增加而提高。气门正时和气门机构应在不久的将来进行优化。