Performance Analysis of Free Piston Expander-Linear Generator for Organic Rankine Cycle Waste Heat Recovery System

Abstract

This study presents a test rig of Free Piston Expander-Linear Generator (FPE-LG) for Organic Rankine Cycle (ORC) waste heat recovery system. Based on the FPE-LG test rig, an experiment investigation on the motion characteristics, indicated efficiency, output performance and energy conversion efficiency of the FPE-LG is conducted. The displacement and velocity of the free piston assembly increase with the external load resistance. The indicated efficiency of the FPE (left cylinder) decreases with the external load resistance. As the external load resistance and intake pressure increase, the peak voltage output of the FPE-LG increases. The maximum peak voltage output is 44.4 V. The peak power output of the FPE-LG initially shows a non-linear relation increase with external load resistance and tends to stabilize in the end. The maximum peak power output of 110 W can be achieved. The energy conversion efficiency of the FPE-LG increases gradually with growing of the intake pressure and external load resistance until the energy conversion efficiency reaches the maximal value, and then the energy conversion efficiency decreases with the intake pressure and external load resistance. The maximum energy conversion efficiency can reach up to 73.33%.  Index Terms-organic Rankine cycle, free piston expanderlinear generator, experiment investigation, motion characteristics, energy conversion efficiency