Experimental and numerical study on the mechanical inconsistency of a dual-opposed free-piston Stirling engine generator

The dual-opposed free-piston Stirling generator (FPSG) presents potential advantages in terms of heightened efficiency, diminished vibrations, and flexible operation. However, the challenge encountered on a dual-opposed configuration posed by components' inconsistency has hindered its progress, and analyses of this inconsistency are infrequently performed in the literature. In response, this study delves into the inconsistency of mechanical parameters, specifically addressing the moving mass of the displacer and the power piston, along with planar spring stiffness, employing both computational modeling and experimental methodologies. A meticulous comparison between experimental outcomes and computational predictions reveals a commendable agreement, with a maximum deviation within 7.3 % for heat-to-electricity efficiency and electrical power. In instances of mechanical inconsistencies, an acoustic power flow within the expansion space transpires, transferring from the generator with a heavier moving mass on the power piston and the displacer, coupled with a stiffer planar spring, to the generator with a lighter moving mass on the power piston and the displacer, along with a softer plate spring. Furthermore, an escalation in the inconsistency of mechanical parameters corresponds to an increased phase difference between the two pistons and the two displacers. It is noteworthy that planar spring stiffness exhibits particular sensitivity to the movements of the moving components. These findings provide valuable perception into the design, manufacture, and control of dual-opposed FPSGs.