Performance investigation of a free piston expander-linear generator for small scale organic Rankine cycle

This paper presents a free piston expander-linear generator (FPE-LG) for small scale organic Rankine cycle (ORC). Based on FPE-LG experiment configuration, performance investigation and efficiency analysis on FPE-LG are conducted. Experiment results show that intake pressure and external load resistance have great influence on actual stroke, velocity and exhaust temperature. The exhaust pressure is hardly relevant to intake pressure and operation frequency. When FPE-LG operates with low operation frequency, the entropy generation decreases with intake pressure, whereas it increases with intake pressure when the operation frequency is high. The indicated work increases when increasing the intake pressure and external load resistance, whereas it decreases when increasing operation frequency. The indicated efficiency decreases with the intake pressure and external load resistance, and the maximum indicated efficiency can reach up to 81%. The voltage and power output increase when the intake pressure and external load resistance increase, and the maximum voltage and power output can reach 44.4 V and 111.6 W, respectively. High energy conversion efficiency can be achieved in the area of high external load resistance and intake pressure. Generally, the higher power output is, the higher energy conversion efficiency is. The maximum energy conversion efficiency of 73.4% is achieved.