Experimental and simulation study of a free piston expander–linear generator for small-scale organic Rankine cycle

This paper presents a new free piston expander–linear generator (FPE–LG) for small-scale organic Rankine cycle (ORC) waste heat recovery systems. An FPE–LG experimental test rig is developed, and a simulation model is established with Matlab/Simulink. Motion characteristics and output performance are discussed based on experimental results, and the simulation model is validated. Further investigation of the motion characteristics and output performance of FPE–LG is conducted at a relatively high intake pressure and operating frequency. Results show that intake pressure and operating frequency significantly affect motion characteristics and output performance. The velocity and displacement of the free piston assembly increase with increasing intake pressure, and the peak power output initially increases then decreases with increasing operating frequency. The peak power output is 676 W when the intake pressure, external load resistance, and operating frequency are 10 bar, 9 Ω, and 15 Hz, respectively. Using the simulation model to study FPE–LG operating parameters is convenient, and the model can serve as a reference for the future design and optimization of FPE–LG.