# The Fluidyne engine

## TL;DR

The paper provides an analytical thermodynamic model of the Fluidyne engine, a liquid-piston hot-air engine, analyzing its motion, temperature, pressure, power, and efficiency based on engine parameters and phase shift.

## Contribution

It introduces a novel analytical approach to model the thermodynamics of the Fluidyne engine, extending methods used for Stirling engines.

## Key findings

- Explicit expressions for piston amplitude and gas temperatures and pressures.
- Numerical analysis of power and efficiency as functions of phase shift.
- Insights into optimal phase relationships for engine performance.

## Abstract

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.