The operation of the Fluidyne heat engine at low differential temperatures

A comprehensive review of small solar-powered heat engines: Part III. Research since 1950—“unconventional” engines up to 100 kW

The circular duct between the cylinder and displacer serves as a regenerator in free-piston Stirling engines. The cylinder wall is fixed and the displacer wall is in reciprocating motion during the steady operation of the engine. The basic equations of the working fluid and regenerative duct are derived using the Lagrangian method in terms of the displacement of the displacer, so that time does not appear in the equations. A relation is derived between the cylinder and displacer wall temperatures to obtain the initial wall temperature distributions. A computer program is written in fortran and the governing equations, which include the pressure fluctuations due to the flow reversals, are solved numerically using a finite difference method. The results and discussion are presented.

Numerical analysis of regenerators of free-piston type Stirling engines using Lagrangian formulation

A paper presented at the 1974 Conference (Ref 1) described the development of a Stirling-cycle thermo-mechanical generator (TMG) for providing small amounts of electrical power continuously over long periods, while requiring much less fuel than other power sources running from hydrocarbon fuel or radio-isotopes. Two of these 25-Watt generators, fuelled by propane, have been used to power the UK National Buoy on two successive missions. A total of more than three years experience at sea has now been accumulated. In addition, a 60-watt version has provided the power for a major lighthouse for more than a year. An early development version of the Thermo-mechanical Generator, adapted to run from the heat of a radio-isotope source, was loaded with strontium-90 titanate in October 1974 and has run continuously in the laboratory ever since. The Paper describes the improvements and changes found necessary in the course of 90,000 generator-hours of running time, and outlines the improvements in operational performance and reliability which have resulted.

Small Stirling-cycle Power Sources in Marine Applications

A high pressure and high frequency diaphragm engine: Comparison of measured results with thermoacoustic predictions

This paper reports results of research at Harwell on thermal energy conversion, which has led to the successful development of an efficient heat engine/alternator system 1 capable of delivering several tens of watts of alternating current. It has no rotating or sliding surfaces, so requires no lubrication, and is believed to be capable of operating continuously for many years without wear or need for attention. It is capable of using heat from a variety of sources and is self starting on application of heat. An electrically heated laboratory model is delivering 25 W a.c. with an overall conversion efficiency of 13%

Thermomechanical generator: an efficient means of converting heat to electricity at low power levels

This paper reports results of research a t Harwell on thermal energy conversion, which began i n 1966 and has led t o t h e s u c c e s s f u l development of an e f f i c i e n t heat engine/alternator system capable of delivering s e v e r a l t e n s o f w a t t s o f a l t e r n a t i n g c u r r e n t w i t h a n efficiency much g r e a t e r t h a n t h a t o f a l t e r n a t i v e methods. This system has no r o t a t i n g or s l i d i n g s u r - faces, so requires no lubrication, and i s b e l i e v e d t o be capable of operating continuously for many years without wear or need f o r a t t e n t i o n . I t is capable of using heat from a v a r i e t y of sources and i s s e l f -s t a r t - ing on application of heat. Three electrically-heated research machines have been built and run, the third delivering an output of 27 w a t t s a .c . w i t h a n e f f i c - iency of 13.5%. Two development machines have been b u i l t and are running, one propane-heated and delivering 31.75 watts a .c ., and one with a r a d i a t i o n s h i e l d for operation with a radioisotope heat source, which delivers 18 w a t t s a .c . Both g i v e a n o v e r a l l e f f i c i e nc y of 10% including a l l l o s s e s from the heat sources.

R. Howlett

Papers

Thermomechanical generator: an efficient means of converting heat to electricity at low power levels

A new electrical power source for long term unattended operation

The Harwell thermo-mechanical generator