> February 19
> Stirling Engines: A New Old Thing
>In 1816, a Scottish Minister, the Reverend Robert Stirling, patented a
>hot air engine with increased efficiency due to the addition of an
>"economizer" or regenerator. The regenerator conserved thermal energy
>as the internal air oscillated between the hot and cold sections of the
>engine. Stirling engines consumed less fuel for equal work and were
>safer than steam engines with their large quantities of energy stored
>The Stirling engine gradually fell into disuse as the steam engine and
>later the internal combustion engine grew in popularity. In 1937, the
>Philips Company began a Stirling engine revival with the development
>of a quiet, multi fuel engine for radio battery charging. Since then,
>designs have been produced all over the world for applications ranging
>from cryogenic coolers, electrical power generation, automobile and
>Conservation and environmental impacts are becoming important
>concerns for energy conversion systems. These issues are driving
>another revival in the development of Stirling engines. These high
>efficiency heat engines with multi-fuel (combustion, solar, nuclear,
>etc.) capability should provide clean, low cost mechanical energy in
>the near future.
>Don Isaac received his BS degree in mechanical engineering from
>Northeastern University in Boston, Massachusetts in 1970 and has
>worked as a design engineer for Square D at the Motor Control Division
>in Milwaukee and later at the Circuit Breaker Division in Cedar Rapids.
>Moving around in the Midwest, he also worked in the welding machinery,
>nuclear plant service, and machine tool industries before departing for
>California in 1979. In California, working for Lockheed Missiles and
>Space, he was involved in projects ranging from underground nuclear
>testing to radiation spectrometers and cryogenic systems for space
>flight. In 1995 he left Lockheed to develop Stirling engines at Tamin
Don Isaac began his talk by explaining that Stirling engine technology is addicting, at least to Mechanical Engineers like himself. The idea was originally thought up by Reverend Robert Stirling in the early 1800s. He patented it in 1816, and ever since then there has been a sort of underground movement to get the idea used in one application or another.
A Stirling engine consists of a gas cylinder, a heat exchanger, a piston, a plunger and some mechanism. One end of the gas cylinder is hot, and the other cold. What happens is that the piston kicks the mechanism when the pressure builds up, which causes the plunger to push the gas in the cylinder through the heat exchanger, which exhausts enough energy to reset the piston, causing the cycle to repeat.
Because one end is always hot, and the other cold, and the same gas is always recycled, the heat cycle is handled very differently than it is in an internal combustion engine, where the walls of the machine stay cool, and the hot gas is expelled. Because of this, a Stirling engine provides a small amount more power at the piston head, but much more power through the radiator, making it much more efficient in applications where that heat can be harvested for other applications. Also, because the engine oil is not being constantly polluted by exploding gas, routine maintenance is about a quarter of that required by IC engines. Also, since fuel is simply used to head one end of the cylinder, changing fuels is much easier than it is for most engines. Another advantage is that a well made Stirling engine is quieter than a comparable IC engine, since there are no gas explosions to muffle.
Stirling engines are not well suited to transportation applications, since they work much better at a constant speed. Because of this, they are well suited to electric generator applications, and a number of companies have tried to build them for this kind of thing. Philips designed one in the late 1940s, and even built 150 of them, but the invention of the transistor made the idea obsolete, and they abandoned the project. There is currently a project in New Zealand by a company named WhisperGen to build a 200 lb. one about the size of a washing machine that can put out about 0.75 kW.
Don Isaac finished the presentation by demonstrating a solar powered one that he brought with him. It had a parabolic reflector to heat one end of the cylinder, and fins along the sides to cool the other end. The flywheel was about five inches in diameter, and had to be kick started to work. Since it was a very gray day, we used a lighter to provide the energy that the sun should have, and it worked very well.