Stirling Engines in the Palm of your Hand
by Lloyd Alter, Toronto on 01.12.06
Treehugger loves Stirling engines-they have been the way of the future since 1816. They work on the basis of temperature differences and can be powered by just about anything- This Japanese toy version appears here to be powered variously by a dog, lunch, a cup of tea and an ice rink- that is versatility! We hope they manage to scale it up a bit. ::Japanese Science Magazine via ::Red Ferret
"The Stirling engine works by the repeated heating and cooling of a sealed amount of working gas, usually air or other gases such as hydrogen or helium. When the gas is heated, because it is in a sealed chamber, the pressure rises and this then acts on the power piston to produce a power stroke. When the gas is cooled the pressure drops and this means that less work needs to be done by the piston to recompress the gas on the return stroke, giving a net gain in power available on the shaft. The working gas flows cyclically between the hot and cold heat exchangers.The working gas is sealed within the piston cylinders, so there is no exhaust gas, (other than that incidental to heat production if combustion is used as the heat source). No valves are required, unlike other types of piston engines." ::Wikipedia
I thought that I saw it here but maybe I didn't. Any way over at hack-a-day they have instructions on how to make your own stirling engine out of aluminum cans!
Every green energy website raves about stirling engines, but what can they actually do? Is there anything useful that's actually powered by one?
Stirling engines once powered cars, in the 1970's. Their development was spurred by the fuel shortage due to the oil embargo. Ford actually produced a car that ran on a stirling engine that was phenomenally efficient; however, the primary problem with the engine was that like all engines that don't run on explosions (and thus burn clean and efficiently), there's a delay between the pedal and the increased power output. And, it took a long time to start up as the engine warmed up. However, the weaknesses of stirling engines could be easily made up for in a hybrid car arrangement.
Stirling engines are actually practical on propeller planes, and some companies have actually developed prop engines using the Stirling cycle. Since most prop planes do not need rapid variations of power output, and since stirling engines get more efficient as the heat sink temperature drops (which is especially true when flying high) stirling engines make amazing airplane engines; too bad they are not more widely used nor known. When I studied engineering at Berkeley, they didn't even teach us about stirling engines in engineering thermodynamics; the stirling cycle was briefly mentioned as a historical foot note.
Stirling engines are making a come-back though. Southern California Edison is in the process of building a massive stirling engine solar energy plant that uses solar concentrators to heat the heat source side of the stirling engines they use. The efficiency of these stirling engines is double that of the most efficient photovoltaic panels at peak sun exposure; on top of that, they track the sun from dawn 'til dusk. Each of the two solar stirling plants will have an output equivalent to a coal-based power plant (at least during the day; I'm not sure if they're storing energy for night time use.)
Re: Stirling Engines.
Kontax (UK) have been selling stirling models for some time now. Pick up your own cool toy!
Sterling engines have some major problems that are VERY hard to overcome
Unless you run with a very high pressure "medium" in the engine (usually high pressure helium) energy densities are quite low, so the weight of the engine is high - if it's in an application that requires the engine to move itself, and accelerate at any kind of speed, there are problems
The other big problem is that the engine runs on temperature diferential - the problem is that there is, by definition, thermal transfer from the "hot end" to the "cold end" of the displacer cylinder, and as the temps start to equalize, you lose power.
Sterling cycle engines were used quite a bit back, oh, 100+ years ago, typically on farms where boilers were too dangerious due to the need for them to be carefully monitored - the best application was probably "pumping engines" - they were used to either pump wells, or pump water out of mines, as the cold water was passed over the cold end, to keep it cold (a good idea) - there were some really really effcient designs, BUT all of them were fairly low power - Look up the Ryder-Ericcson pumping engine
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