A closed-loop linear engine generator using inert gases: A performance and exergy study

This paper introduces air, argon, and helium used as working fluids in a first-of-its-kind closed-loop Linear Engine Generator (LEG) to reveal its performance map, energy flow, exergy destruction, and exergy efficiency. Properties of the working fluids affect the LEG designs, e.g., compression ratio and applicable temperature range, in turn, impacting system efficiency and power output. A comparison is made between open-loop and closed-loop models using air at a peak temperature below 1095 K, based on a laboratory prototype of an open-loop LEG. The closed-loop models using air, argon, and helium achieve impressive efficiencies of 43.92%, 43.74%, and 51.30%, respectively, at the intake pressure of 0.85 bar and intake temperature of 225 K. The LEG using air shows the highest power output of 2448 W, while the helium version generates 2044 W and the argon version 1850 W. The exhaust energy loss is one of the major energy losses, which is comparable to the mechanical power output, while the friction loss ranges from 7.4% to 9.3%. The compressor and expander have low exergy destructions and high exergy efficiencies of more than 96%. In the closed-loop systems, the maximum exergy destruction rate is seen at the condenser affected by the coolant's low temperature.