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Van Blarigan's experiments suggest that these engines could be 50 percent efficient at generating electricity--close to the efficiency of hydrogen fuel cells and much more efficient than conventional generators. Free-piston engines are efficient in part because they have fewer moving parts than conventional engines do. The engine configuration also makes it practical to tune the engine so that the fuel in a combustion chamber burns very quickly. Faster combustion allows the engine to get more work out of a given amount of fuel, improving efficiency. It can also improve emissions.
The free-piston design can also allow the engine to be instantly optimized for different fuels, such as hydrogen, natural gas, ethanol, gasoline, and diesel. Ideally, drivers could use whatever fuel is cheap and readily available.
The development of free-piston engines, however, is still at an early stage. "The free-piston has some unique features--simplicity and variable compression--which make it intriguing," says Gary Smyth, the science director of GM's Powertrain Systems Research Lab. "But [they] also pose a number of challenges."
Van Blarigan says that one major concern is the sound of the engines: the fast explosions are very loud and will be difficult to muffle. But perhaps the biggest issue is control. In a conventional engine, the movement of the pistons is constrained by the rods and crankshaft, which help even out any variations from cycle to cycle. The free-piston engine is more flexible. That allows for using different fuels, but it makes necessary some sort of active control mechanism to ensure that each cycle is the same: variations could cause poor performance and increased emissions. High-speed computers and the ability to electronically control piston movement in a free-piston generator (via the coils and magnets) could help engineers solve this problem.
Whether the engines will be significantly cheaper and more efficient than conventional engines is unclear, says John Heywood, a professor of mechanical engineering at MIT. "There's been enough development to say that it works. But with very different engine geometries, it's hard to work out just how good it is. Is it really better?" As research progresses, it will need to answer questions about efficiency, emissions, performance, and especially cost, Heywood says.
Meanwhile, conventional internal combustion engines keep getting better, which could make it difficult for the free-piston design to get a foothold.
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It would appear to me that this is ultimately more incremental than the way we think about hybrids or electric cars. In this scheme -- bottom line -- we are using an internal combustion engine to generate electricity, and driving the wheels with the electricity. It "works" only because the new design of the internal combustion engine, combined with the known high efficiency of the electric motor, result in a higher efficiency than a conventional internal combustion engine.
The article makes the point that improvement in conventional engines will continue, and will compete with this relatively incremental improvement. That is known as the "sailing ship effect", and is well documented. (For instance, see http://www.thecis.ca/index.php?catID=32&itemID=52)
DaveT
I wonder why one couldn't couple such an engine with thermo electric devices to improve efficiency--also there is emerging technology which converts sound directly into electricity--the loud noise produced might actually be a plus
Thermoelectrics are intriguing, but only at very high temperature differences. Otherwise, they have low efficiencies. Some applications are being developed to harvest energy from the high temperature environment of combustion engines. The use of thermoelctric devices is practically an admission of poor thermal efficiency, because quite a bit of waste heat must be present first.
I agree with your comment on the noise being a plus. That was my first thought too, since many people complain that electric cars don't have that great noise they love. The problem with this engine and two-stroke engines as well is that the noise gets way too high compared to an average car.
Van Blarigan says that one major concern is the sound of the engines: the fast explosions are very loud and will be difficult to muffle.
Noise Problem solved here:
“…engineers…are turning to innovative materials that make possible a new approach to the physics of noise reduction…” :
http://www.sciencedaily.com/releases/2008/09/080929163717.htm
“…Nadler has developed what could be the world's first superalloy micro honeycomb using a nickel-base superalloy. At around 30 percent density, the material is very light – a clear advantage for airborne applications – and also very strong and heat resistant.
He estimates this new approach could attenuate aircraft engine noise by up to 30 percent. “
The piston free engine is already here
The team at Cyclone technologies already have a piston free engine that uses a cyclone to efficiently and cleanly refine fuel as it burns, without the worry of of the noise level of shuttling parts. By having a self refining engine, you can use nearly any fuel, including dried algae.
It doesn't need water pumps, oil, or transmissions. It also is powerful enough for direct mechanical motion instead of having to convert the mechanical energy to electrical energy, store it, and then change back to mechanical energy again - each step with its own energy losses.
http://cyclonepower.com/index.html
Don't turbines also have the advantage of flexible fuel source? Tesla/bladeless turbines are cheap and simple to build.
This design would be perfect for using production gas made as syngas from pyrolsis of wood waste. The flue gases could be used for heating purposes and as a source of nutrient for growing algae (products of combustion), for sequestration of CO2, for production of electricity, and for CHP applications.
I just typed a simple search: "Free piston Stirling engine" and came up with this entry in the first few places: http://www.sunpower.com/index.php
If you got to the second paragraph, you'd read that it is not new. But it has more R&D than in times past because of the new application of PHEV or REEV (like the Prius has put in use the Atkinson engine instead of the typical Otto engine).
Compressed air can also be used to power such an engine without any tailpipe exhaust and much lower wasted heat energy. This may be just the way that compressed air technology (CAT) becomes incorporated into a future design. The current technology attempts to power a drive train, but it would be simpler to use this free-piston design to generate electricity. It would likely be quieter and more controllable than explosions. It would definitely be lower temperature.
Along with the free-piston engine, there are wankel-type designs for compressed air that could easily generate electricity rather than turn a shaft.
A big advantage to compressed air is the reduced weight because of the radically lower temperatures and pressures.
Not new. Free piston gas generators(compressors) were use in German U boats in the WW2 era. Stanford has an operational one in their engineering lab. Also The Swiss currently have a very advanced generator model.
I am pleased to see the use of the two stroke cycle, but the bottom of each piston should be used to pre-compress the next charge. You should really have the advice and consultation of the Outboard manufacturers, most advanced is Mercury Marine in Fond du Lac, Wisconsin. They also use low pressure direct injection, which is much better for fuel consumption, efficiency, computer matching and effluents. Also they have much skill at tuning of exhaust, to control the use of reflected pulse pressure to supercharge and control the exhaust, etc.
I am surprised at your lack of state of art search or knowledge.
Is there a problem with heat management with an engine that doesn't have a drive shaft? I mean, won't the piston get unusually hot?
Yes, the piston will get hot. And in this design it contains a magnet that will be demagnetized if it gets hot. That's one of the many problems between making one of these work in the lab, and making it work well enough to be useful. Note that you not only need to make the engine efficient, but you need to make the generator efficient. Making efficiency generators is generally easy, but not in this configuration.
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ryuuguu
45 Comments
Free Rotatory Engines
I wonder if there would be any advantage to using other engine configurations with out the drive shaft conection. Such as the Wankle or others.
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honzik
14 Comments
Re: Free Rotatory Engines
One advantage of using an engine like the Wankel or the RadMax engine is that the two separate components can be manufactured and optimized as two separate subsystems. Free piston engines with both heat engine and electromechanical components might introduce too many complications in jointly optimizing the two systems, preventing it from eventually making it to market.
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