Simulation, manufacture and experimental validation of a novel single-acting free-piston Stirling engine electric generator

Owing to its high thermal efficiency, fuel flexibility, low vibration and noise, and low emissions, the free-piston Stirling engine has in recent years attracted renewed interest worldwide for uses specifically relating to micro-combined heat and power generation. To aid prospective engine designers with the modelling and analysis of such engines, this paper presents the numerical simulation, manufacture and experimental validation of a free-piston Stirling engine electric generator. The paper firstly presents a 100 W electrical free-piston Stirling engine developed at Stellenbosch University. Secondly, an overview of a fully-explicit, one-dimensional numerical model is given in which both the engine thermodynamic and kinematic behaviours are solved as an initial-value problem. Thirdly, an experiential case study of passive engine operation is presented in which a peak electrical output of between 60 and 70 W was delivered. The obtained experimental data clearly validates the numerical model, with the piston stroke deviating by 2.61%; the piston-displacer phase difference by 12.42%; the workspace indicated power by 15.15%; and the average electrical output power by 23.30%. For future work it is recommended that the validated model be used to develop a more optimised and task-suited engine. The use of an active feedback controller is also recommended so that piston-casing collision can be eliminated.