  The Fluidyne is a two-part hot-air engine, which has the peculiarity that
both its power piston and displacer are liquids. Both parts operate in tandem
with the common working gas (air) transferring energy from the displacer to the
piston side, from which work is extracted. We describe analytically the
thermodynamics of the Fluidyne engine using the approach previously developed
for the Stirling engine. We obtain explicit expressions for the amplitude of
the power piston movement and for the working gas temperatures and pressure as
functions of the engine parameters. We also study numerically the power and
efficiency of the engine in terms of the phase shift between the motions of
piston and displacer.
