Conventional closed cycle heat engines — such as Stirling engines — have many advantages, such as high theoretical efficiency and the ability to produce useful work out of any heat source. However, they suffer from low power density due to poor heat transfer capability between the working gas and its surrounding walls. In this work, we proposed a new architecture where the solid displacer of a Stirling engine is replaced with a ferrofluid liquid displacer. In this approach, the relative displacer location with respects to the engine chamber is controlled (and stabilized) through a strong magnetic field generated by a permanent magnet. The liquid nature of the displacer allows the hot and cold chambers of the engine to be filled with porous material, improving the heat transfer by an order of magnitude. Additionally, this engine architecture mitigates sealing issues, can operate at higher pressures, and has naturally lubricating surfaces. A relatively simple configuration of this idea is modeled in this work. Exploratory dynamic simulations of this unoptimized architecture show a thermal efficiency of 21% and a power density of approximately 700W/lit.

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