Operational Characteristics of Liquid-piston Heat Engines

Liquid piston Stirling engines (sometimes termed "fluidyne" engines) have been studied, proposed, applied in a variety of energy conversion applications including water pumping and electricity generation from solar energy. They are attractive for low capital costs and simplicity of construction. In addition, their operation as external combustion engines allows for flexibility in primary energy sources which is a distinct advantage when a low-cost or free source of heat can be paired with their minimal construction costs. Disadvantages of these devices include relatively low efficiency and low power density.      This paper describes test results from a solar-powered fluidyne engine utilizing a Fresnel lens for concentrating solar energy, and from a combustion powered engine equipped with an orifice-style dynamometer for controlled loading of the engine.     Temperature, pressure, and volume phasing along with indicated work and brake work are presented and discussed. The Fresnel lens provided ample power for sustained operation of the engine, and engine cycles and operational characteristics of the solar powered engine are discussed. Operating without load, the pressure and volume phase difference was 72 degrees and the dynamic mechanical response showed no delay from the thermodynamic expansion due to temperature changes of the working fluid. The function and capacity of the orifice-style dynamometers are evaluated for testing various configurations of liquid-piston engines under load. Engine cycles and operating characteristics of the loaded engines are presented and discussed. Relative sizes of indicated work and brake work are explored as functions of engine configuration.