Mike Phillipps Its a Stirling engine! en.wikipedia.org/wiki/Stirling_engine . Ive studied them extensively. Its similar to a steam engine in that the fuel is burned on the outside, but the working fluid is actually purely a gas, like air! The water thats used there is just to cool the outside, like in a car radiator. The movable steel wool / (or stacked metal wire mesh) piece is a unique type of heat exchanger called a regenerator, in this case moved directly from the crankshaft. In more advanced designs that piece is stationary, and there is a moving displacer instead. The rubber balloon is a diaphragm piston. The piston rod, crankshaft and flywheel shown are common to any piston engine. By the way, Im a big fan of the diaphragm piston for a Stirling, because it avoids the problems of a sliding-seal piston, which requires tight tolerances, develops friction and wear, and generally isnt lubricated with oil to avoid clogging the regenerator, or risk explosion in a pressurized air engine. Low temperature engines like the one shown above are common novelties but generally only produce enough power to turn themselves, and even then only with a fair amount of tinkering to get each one tuned-up just right. Sure, you could make a huge one with a 55 gallon drum, but it would be bulky and still wouldnt produce much power. Plus youd have to operate and maintain the thing, so thats where most folks opt for: grid electricity, generators, solar cells and/or batteries. If the Stirling interests you anyway, you might check out the Fluidyne that uses a liquid piston, and is a hybrid Stirling - steam engine. The most famous book authored by West. youtube/watch?v=SNxR-lEZXoQ To get more power out of a Stirling engine, you have to either increase the working volume, pressure, temperature, or use a lighter gas like Helium, all of which present significant design challenges. Stirling engines are great in theory, but often arent so practical in reality. They dont really scale-up linearly. Doubling the size doesnt necessarily double the power. They are good engines for high value, low power (10-100W) off-grid applications requiring low noise, and sometimes efficiency and high reliability, but even these potential advantages are challenging to obtain, at least to the novice. The basic technical problem is that it is just difficult to move a lot of heat into and out of a gas quickly and inexpensively using heat exchangers. *Internal* combustion engines, (like common gasoline/petrol (Otto) engines, and diesel engines) do this much more effectively by heating the gas directly, and then not bothering to cool it for the next cycle, but rather just exhausting it and replacing it with fresh air. There are *zero* heat exchangers in the thermodynamic cycle, just a radiator to keep the engine from overheating. The challenge with *internal* combustion engines is that there are limitations on the fuel. It has to be refined and filtered so that it burns cleanly, and doesnt gum-up the engines precision moving parts. Stirling type devices are also good as cooling devices, for small cryocoolers, mainly used in night-vision goggles. Coleman made a picnic cooler at one point, but it was expensive, and probably didnt sell a lot of product. A simple block-of-ice works surprisingly well for cooling, and its not so easy to improve on that. The theory to understand Stirling devices well is also extremely complicated (math & physics). I put together this article awhile back to help explain the thermodynamic cycle: en.wikipedia.org/wiki/Stirling_cycle Even though the concept is a century old, only in recent decades did Dr. Organ solve the thermodynamic design problem with his scaling methods. There are even some open-source design & simulation tools kicking around, like GCS and QSFM respectively, which might still be available on the yahoo group Hot air engine society (HAES) if they havent been deleted yet.
Posted on: Sun, 14 Dec 2014 15:51:25 +0000