I knwo we’ve done a lot of Stirling in the past (though, surprisingly, a 30-day search only turned up one thread), but Dean Kamen’s intro. of his Stirling engine suddenly knocked it all out of my head and me wonder what the heck the advantage of it was (he’s touting it as a water distiller).
Would it ever replace IC in cars? Or could it be used to capture some of an IC engine’s waste heat to generate power (in a hybrid vehicle, say)?
The short answer to your question is: no. Stirling engine’s don’t like to be ran at variable speeds, and since cars run at variable speeds, a stirling is a poor choice for the car. There’s also the problem that the temperature difference tends to equalize itself in a stirling engine, thus depriving it of it’s ability to run. Of course, will billions of research dollars poured into stirling engines, one might be able to come up with a workable design, but other than the odd hobbiest, there’s no one persuing research into stirlings.
Some recommended sources of further info:
Could the fact the continuously variable transmission (CVT) is now practical for use in a car make a stirling engine workable or are the other problems to great to overcome?
Plus as toadspittle asked in the OP, if a stirling engine was being used to generat power for a hybrid vehicle it would only have to run at one speed.
The CVT really wouldn’t do much so far as improving the operating conditions. The best bet would be to put it into something like the Toyota Prius or Honda Insight, which have a small gasoline powered engine, hooked up to a generator which then powers an electric motor that drives the car. AFAIK, no one’s gotten the same amount of horsepower out of a stirling as they have of an ICE of the same size or smaller. Possibly, it could be done, but it’d take lots of research dollars which no one is willing to pony up at this point.
There wouldn’t be any benefit from this at all. Any horsepower gains made by not having the alternator hooked up to the engine would be cancelled out by the added weight of the stirling engine. You’d have better luck hooking up peltier junctions to the engine to get power. (Peltier junctions work almost identical to stirlings. If you apply heat to one side and cold to the other, you get an electrical current output. If you apply an electrical current to a peltier junction, one side gets hot and the other cold.)
It’s not totally impossible that a stirling engine could be made to work in a car, just incredibly expensive. When you factor in the R&D costs simply to build a workable design, and add to it the costs of converting an entire industry over to the manufacture, distribution, and support of the stirling engine, it’s pretty much a deal killer, unless you can work out a very cheap design.
What about a hybred electic car where the engine turns a generator and the wheels are powered by an electric motor.
Again, until someone can come up with a design for a stirling that has the same horsepower to weight ratio as an ICE, it’s simply not practical. There’s also the problem of “heat death.” A stirling works because one side is hotter than the other. Eventually, that heat will migrate to the other side of the engine and it’ll grind to a halt. This occurs even if one uses a cooling system on the engine. There may be ways around this, of course (there’s a guy who’s developed massively strong ceramics which might work), but again, you have the cost problems of R&D and converting the industry over to the new standard.
While not about Stirlings, there is related info in this thread about steam powered cars.
I’m not sure I understand this. Why can’t a Stirling engine exhaust its waste heat to the atmosphere the way an ICE does (e.g. with cooling fins or a radiator), thus maintaining a temperature difference between the hot end and the cool end?
Okay, here’s the basics of how a stirling works:
Picture a long tin can. Inside of that tin can is a shorter tin can of almost the same size diameter as the outside tin can. Got it? Now, add heat to one end of the large tin can. The air inside that tin can expands, pushing the smaller tin can to the opposite side of the larger tin can. This in turn, compresses the air in the side of the tin can that’s not being heated, as the air’s compressed, it wants to heat up and expand. As it does so, it forces the inner tin can back to the side that’s being heated. Which in turn, compresses the air in that side of the can causing the air to push the inner tin can back towards the unheated side, where the air has cooled slightly due to expansion. The problem comes in when you factor in the facts that the tin cans conduct heat. So, the inner tin can heats up from the compressed air, and the outer tin can heats up from the heat that’s being applied to it. As the air inside the can gets hotter, it becomes harder to compress, thus forcing the engine to work harder to do the same task. Eventually, even with a cooling jacket around one side, the piston gets so hot that the engine can do no practical work. One could theoretically make the engine out of an exotic ceramic which wouldn’t conduct heat, but you’d still have the problem of the outer tin can getting hot and transferring its heat to the other side of the tin can that’s supposed to be cool.
Again, I’m not saying that it’d be totally impossible to develop a workable design, merely expensive and difficult. For an example of a ceramic that would work, check out this site.
I guess I understand what you are saying, but it seems to me that as long as you can maintain a substantial heat difference between the hot and the cool ends of the Stirling engine, you should be able to do useful work.
As I understand it, there are (at least conceptually) two pistons in a typical SE: one has the job of shuttling gas between the hot end (where it’s heated) and the cool end (where it expands and cools by driving the second piston, which does mechanical work). I don’t see how the pistons heating up should cause the death of the engine – that would come if both the hot and the cool ends trended toward the same temperature, but if you have a decent way of exhausting heat, that shouldn’t be the case.
It’s possible that I’m dealing with theory whereas you are describing the practical behavior of some engines. I have a friend with a bunch of working SE models. I have watched one go for around 20 minutes with no apparent decrease in its speed, but perhaps that’s not long enough for the problem you cite.
The next time I see him, I’ll ask him to run one overnight (he has one that runs – albeit slowly – off the heat of a 15w light bulb).
There’s only one piston! Only one! And it’s also hard to see the engine slow down if it’s not asked to do any work, which it sounds like your friend’s engines aren’t doing anything other than simply running.
I checked the HowStuffWorks website and they mention Stirling engines with both a displacer and a power piston (and they have a picture of one with 2 pistons). I know that my friend has several with 2 pistons. So, while there may be single-piston versions, these are not the only type.
An engine that is “simply running” is still doing some work, overcoming friction.
Yes, but it’s not doing any “useful” work. An engine with no load on it will run longer and use less fuel than an engine with a load on it. So while you might be able to get (wildly grabbing numbers) a 1,000 hours out of a stirling with no load before “heat death” occurs, once you put a load on that engine, the amount of time before “heat death” occurs is going to be considerably less. (How much less depends upon the efficentcy of the engine and the amount of load place upon it.)
Stirling engines convert a heat difference into work, they do it very efficiently and over a wide range of temperature differences.
A Stirling engine can be put in a car - it has been done. But for various reasons - already mentioned by others - they are not really suitable.
It is certainly not the case that the Stirling engine is just for the hobbiest - although they are very popular with hobbiest for a number of reasons, not the least of which is that there is no boiler full of steam to explode as there is with a steam engine. There are all manner of designs here is a particularly interesting one: http://www.trochilicengines.com/animations/.
A popular practical use for the Stirling engine is in solar power projects (http://www.sandia.gov/media/NewsRel/NR2000/solar.htm). A dish or trough is used to collect heat that is then converted into power by a Stirling engine. In some cases, the a gas burner is used to provide heat to the same engine during the night.
NASA has, it seems, been experimenting with a Stirling engine for use in space probes (http://spacepwr.jpl.nasa.gov/stirling.htm) presumably to replace or supplement power from Peltier effect generators used on current space probes - a Stirling engine will get you loads of power, but for all its simplicity, it still has moving parts.
I remember reading that some military submarine(s) were fitted with Stirling engines because they were quiet.
http://www.soton.ac.uk/~engenvir/environment/transport/tr_altrn.htm
It depends upon the type of boiler you’re using. There’s what’s known as a “flash boiler” which is highly unlikely to explode.
My dad makes minature super-efficient stirling engines (they have run off the heat of the VCR for 6+ weeks) and when I asked him if they were good for anything, he said stirling engines can be used to pump water on farms (?) and that there have been attempts to make vehicles run by stirling engines.
He also said that the guy who invented the Segway has a patent on a new type of stirling engine. I don’t know anything else about that, though.