A comparison study and performance analysis of free piston expander-linear generator for organic Rankine cycle system

Abstract In this paper, a free piston expander-linear generator (FPE-LG) experiment rig equipped with different linear generator (LG) is established. A comparison study on the performance of FPE-LG with different LGs is conducted. Then the operation characteristics and output characteristics of FPE-LG are investigated. The results show that the selection and design of LG has significant influence on FPE-LG performance. The displacement and velocity with LG-1 are higher than that LG-2’s, but the operation stability and output performance with LG-2’s are better. Considering the high pressure and temperature operation conditions in ORC system, LG-2 is suitable for this experiment rig. Both actual stroke and velocity increase with intake pressure and external load resistance. The variations of actual stroke, velocity, indicated efficiency, voltage and power output are more sensitive to intake pressure than external load resistance. The maximum power output can reach up to 111 W. The voltage output is in agreement with that of velocity. The peak voltage output is usually obtained when the velocity reaches peak value. The energy conversion efficiency shows first increases and then decreases with external load resistance and intake pressure. The maximum energy conversion efficiency of 74% can be obtained.