A dynamic model of a free liquid piston that exploits piston geometry to produce a high inertance was developed for use in a free piston engine compressor. It is shown that for the size scale targeted, advantageous piston dynamics can be achieved with a reduced piston mass compared to a rigid piston design. It is also shown that the viscous losses associated with the liquid piston are negligible for the application discussed. The slow dynamics achieved by the liquid piston also allow for reduced valve sizes for the compressor, creating a more energy-dense device on a systems level. Other advantages gained by this design compared to prior work are discussed, including the elimination of a separated combustion chamber, smaller (integrated) pump check valve, and the capability of more balanced operation for a single-piston compressor. A dynamic model of the proposed high inertance liquid piston is presented and simulation results are discussed.

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