This is an archive of past discussions about Stirling engine. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.
I wonder if Stirling technology could be an answer to solar energy production, at least on a small scale. Since a direct solar -> electrcity solar cell is pretty inefficient (maybe 20% now, was only 10% for a long time), I wonder if a better approach might be to use a solar collector to heat water in a closed system, apply it to a stirling engine that then turns a generator. Since the solar collector itself is about 80% or more efficient, and the stirling engine is 50%, and the generator perhaps 85%, the overall losses are much less. Anyone think this idea has merit? I'm not sure how big a Stirling engine needs to be to be useful here, but I can envisage a (trans)portable power supply unit that would be self-contained and be great for e.g. the African or Australian bush. Graham 10:13, 5 Aug 2004 (UTC)
Check out http://www.stirlingenergy.com to see someone who is doing essentially what you've just suggested. Interesting stuff. Don't know how competative it is. --Flatline 18:04, 2005 Jun 1 (UTC)
0.8 * 0.5 * 0.85 = 0.34. 34% efficiency overall. I'm actually looking into using the excessively-hot solar collector water to drive a sterling cycle cooled by a geothermal pump. I might write this into a book too. --John Moser23:23, 13 December 2006 (UTC)
Regenerator is essential component of a Stirling Engine
From countless references including this history of the Stirling Engine:
"The Rev'd Robert Stirling applied for the first of his patents for this engine and the 'Economiser' in 1816, a few months after being appointed as a minister in the Church of Scotland at age 25. Others such as Sir. George Caley had devised air engines previous to this time (c. 1807) and other devices called air engines were known as early as 1699. The 'Economiser', or regenerator, has come to be recognized as a most important portion of the patent of 1816. These innovations were even more remarkable in light of the fact that they preceeded the birth of thermodynamics and the writing of M. Sadi Carnot by some 40 years!"
Many variants of hot air engines existed before the Stirling Engine. They are not all Stirling Engines.
The article states that the regenerator is a part of all engines calling themselves stirling engines, yet the first diagram on the page has no regenerator. Sweavo09:04, 29 May 2007 (UTC)
External links inflation
Some authors seem to have a misunderstanding about our linking policy. The Wikipedia is not a web directory. It would be most helpfull, if someone knowledgeable in the field would expend some time distilling the links to the most important ones only. --Pjacobi 10:46, 2005 Jan 16 (UTC)
Can you supply a link to the linking policy, please? Paul Beardsell 11:07, 16 Jan 2005 (UTC)
Sorry, it seems I was overly bold in my previous comment. Besides the sparse mentioning in Wikipedia:What Wikipedia is not, I wasn't able to find a written policy. So in contrast to the German Wikipedia, which seems to be more formalistic in this area, the handling here relies on precedent on discussion. --Pjacobi 22:39, 2005 Jan 16 (UTC)
But I agree you with you: There should be a policy. If in the "external links" section we just cut'n'paste everything returned by Google then we might as well just have one link which will always be up to date: Google search for "stirling engine". Paul Beardsell 23:06, 16 Jan 2005 (UTC)
Isn't it pretty important that the reference for all statements made in the article be there? Taking out the links is in conflict with that priority. 208.180.52.10803:11, 21 September 2007 (UTC)
Cycle description
I'm a little unhappy with the description of the Stirling cycle in the opening paragraph - if some mechanical engineering type doesn't fix this, I may be forced to be bold. I'll have to see the "thermodynamics" article and the Carnot articles and see if there's a discussion of other thermodynamic cycles that could be referenced here. I took out the "hot air engine" link because it linked back to this article. I've tried to put back in some of the disadvantages in earlier version of the article, since they are important. There were a couple of odd-looking sentences that I zapped. And I agree, way too many external links...someone with high speed Net connection should do some pruning. --Wtshymanski 17:05, 24 Mar 2005 (UTC)
Thermoacoustics
One of the most exciting stirling applications (in my opinion, anyway) is thermoacoustics. The lack of moving parts and the potential for miniaturization are both pretty important...why no links or other mention on this site?--Joel20:41, 9 May 2005 (UTC)
The concept of the external combustion engine with sealed internal gas is becoming generally accepted as the description of a Stirling engine. Thermoacoustics is simply running a very specialized Stirling engine backwards. The world has so little awareness of the Stirling engine, which I don't understand. Let's not split hairs on the topic and make it more difficult for people to learn about this. The process needs a name.
Bptdude03:08, 30 May 2006 (UTC)
That is *NOT* the "generally accepted" description of a Stirling engine. The accepted definition of the Stirling engine is one that uses the Stirling thermodynamic cycle. (Instead of, for example, the Carnot cycle). Few of the theromoacoustics devices are Stirling Cycle. What is a reference for this alleged change of terminology in the field?
FYI - Here is a cool (sic) sight that gives a a simple explanation of thermoacoustics currently being used by a major corporation, Unilever, in one of their ice cream divisions.
Added a comment on the category of Free Piston Stirling Cycle engines, plus a reference. Note that this is one of those areas with a reasonable print publication history, but almost nothing in Google. [I notice a lot of wikipedia reflects Google, and ignores the non-net history of topics]
Should Franchot configurations be mentioned specificly under Alpha? [They are the only configuration I'm aware of that allows BOTH pistons to be replaced with a diaphram.]
While the "engine out" emissions of the engine are quite low, further catalytic cleanup of NOx (oxides of nitrogen) is made challenging because of the lean (excess oxygen) nature of the exhaust.
This isn't a problem of the engine itself but the heat source. Except for vacuum engine (others ?), the engine is closed. For example, how can NOx be generated for dish-stirling engines (solar source) ? I'm not native english speaker then can somebody correct ?
Topic
When we are talking about stirling engine, Cryocoolers should not be included in the same article. Brief introduction of 1/2 lines is ok but a section should not be there .
Compression ratio
The gamma stirling description talk of a this configuration having a lower compression ratio , but this measure is only really significant in internal combustion engines. What is the article getting at here? Or is the compression ratio article wrong? Lumos309:36, 26 January 2006 (UTC)
The compression and power strokes are comparable in the Stirling and gasoline engines. In one, you heat the compressed air by exposing it to a hot heat-exchanger. In the other you heat the air by burning fuel in it. The article is comparing the Gamma to the Beta configurations. In the Beta, the displacer overlaps the main piston to some extent, so you can have a smaller total volume and a higher compression ratio. I don't see it as a very important distinction. Mackerm21:19, 26 January 2006 (UTC)
The compression ratio in an internal combustion engine is ~8-20, and in a Stirling engine is closer to the temperature ratio ~(1.5-2.5).
The refrigeration industry, and it's considerable dependence -- in mechanical refrigeration -- on a compressor, the compression ratio is a function of discharge absolute pressure divided by absolute suction pressure. It has little to do with the mechanics of the compressor. What ratio is being discussed here? 216.231.162.913:49, 29 April 2007 (UTC) ART PEREZ P.E.
solar stirling engine
I couldn't add to the top paragraph, so I'm adding a new discussion. There are small models that can be purchased, that have shiny satellite looking dishes that heat the center which drives a Stirling engine.
But the openening paragraph asked about using a solar collector to heat water to feed a Stirling engine. This really shows people's misconception of this type of device, trying to force the square peg into the round hole of what is commonly known.
To use a Stirling engine powered by solar energy to produce energy, you might find a location in Death Valley where 100 feet underground ran a cool water flow. Between these two, you built a mile square extremely simple Stirling machine, that went round and round, driving an electrical power plant.
What is holding up deployment of Stirling engines is more popular perception more than economic, evironmental, or technical issues. The public need only two pieces of information, really. How much of a temperature difference do I need for the current practical Stirling engines? How much does the engine have to cost at current oil prices to pay back an investment in X number of years? When people think of Stirling engines like they think of hydroelectric generators that produce as long as the river keeps flowing, they will begin to get the idea.
I couldn't help but think of how to deploy solar Stirling engines in a desert area. I was surprised to find out there is a project underway to deploy thousands of shiny reflective dish type solar Stirling engines in the American Midwest. I saw the details but didn't record it. I'll find it again and post. The most interesting feature, besides the now financial practicality of energy generation, is that the solar Stirling engines are considered safer for the environment than wind turbines. They don't make the noise and don't kill the birds.
But I was thinking about trying to design a Stirling cycle that could use the intense heat of the day and the very cold of the night to power a large scale Stirling engine, even though the two opposite temperature sources are half a day apart. This kind of Stirling cycle might be very welcome in developing nations that don't have much in the way of other resources.
One interesting use of a solar Stirling engine might be on the surface of the planet Mercury. There, where one side always faces the sun, the line between day and night doesn't move and the temperature difference is intense between the light side and dark side. The distance between the temperature differences can be merely a matter of feet.
Somehow I don't think they are going to sue me! *smiles*
begin of cut from web site
The SES dish system was initially developed by McDonnell-Douglas in the mid 1980's. Since 1998 SES and Boeing have been under contract with the Department of Energy’s Sandia National Laboratories for a Dish-Engine Critical Components (DECC) program.
What geographical areas are best suited for a solar dish farm?
The southwest region of the United States is ideally suited for this. In fact, a solar farm 100 miles by 100 miles could satisfy 100% of the America’s annual electrical needs. Solar technology primarily addresses the peak power demands facing utility companies in the Southwest U.S. and other solar-rich areas.
end of cut from web site
OK, I have a question. If the above is true, why isn't somebody running for president up on this soapbox?
the statement probably assumes 100% efficiency so more land would be needed.
no, not that silly to assume 100% efficiency. The estimated area for 100 square miles of open desert to supply the total amount of the United States electrical generation needs comes from a study produced by Sandia National Labs in very precise gory detail. If anything, it should be assumed the efficiency of the engine would have increased, thus decreasing the required land area. Also, with only precise manufactureing costs driving the price barrier, not any rare materials, dangerous procesess or other restrictions, it could be assumed to be only a matter of clock ticks before a better engineered commercial solar sterling elctrical generator will be manufactured in places like China, to produce hydrogen, if not direct grid power, thus answering the question of what to do for power at night, and how can this also replace hydrocarbon fuels for transportation fuels. Sadly, China may be producing them in China not for low cost exports to USA, but to be placed in the Gobi desert to power China electrical grids. People here will still be trying to sponsor pork barrel projects to produce power from corn, or coal, or build nuclear reactors.
Bptdude07:07, 2 May 2007 (UTC)
Trying to supply the entire nation with energy from one location is crazy talk. The loss of power due to the resistance of the electrical cables would chew up enormous amounts of the energy produced, not to mention the security risk it would propose. --Powertrippin (talk) 05:11, 10 March 2008 (UTC)
Oh, Powertrippin. Crazy talk? I would think you are pretty funny, but most minds involved in this are similar to you, even "experts". We can disregard the security risk. We are not talking about a single supersizd nuclear plant or something, we are talking about relative capacities. If we could generate what the nation uses from one site, you can be sure more would be built to greatly increase capacity, and built in other locations. The absurd part, and no insult to you, is assuming we would use cables strung on towers to have it ready for some corporations end-of-year financial statements.
OK, here is a clue. Instead of spending an extra trillion or two a year to "bring democracy" to nations with lots of oil, etc. we could have some imaginary president who actually has vision, commit the United States to the massive project of coversion of our energy infrastructute to a hydrogen based economy. All solar power Stirling can be coverted to hydrogen and shipped to anyplace in the country. This would of course open up for any other form of green or semi-green forms of energy production, providing an interface for any industry to be on equal footing, such as coal power if they can bury the carbon, or nuclear built as far from cities as pratical that just make hydrogen, or wind, or anything else. Iceland is an entire nation on a hydrogen based economy built by Royal Dutch Shell Hydrogen Ltd. It is only a matter of time anyways, as nations bordering the Sahara are already starting to figure it out, and Brazil knows they are also in a huge sun belt. Solar is easy pickings, and the Stirling cycle is not the only means to harvest it.
Please do not call crazy what you just do not understand based on what is done now in a long accepted way.
PS - With plentiful hydrogen made cheap, "experts" like you, still on offence, will point to all the problems with fuel cells. Bah, humbug. If hydrogen was plentiful and cheap, we can bring back 1970 mussle cars, with the original internal combustion engines, slightly tweaked, with a fancy and a little pricy hydrogen fuel tank, but rip out all the emmision controls, since the exhaust will just be water and the power of hydrogen is greater than gasoline. VARROOMMM !!! Screw the frugal fuel use, let us do it the real American way, make the pie bigger. Here is also a clue. The Chinese are working on this, desperate for energy independance and rapid massive growth. Only the cheap reliable Stirling engines they engineer might be more used over there, instead of imported here, while our new leaders argue how to reduce greenhouse gases by 10 percent in 20 years and how to setup carbon credit stock exchanges.
Fine, call me crazy. By the time you realize I am not, it will be too late, and seem obvious and simple. Some great Illuminaty conspiricy will be blamed or whatever, by the "sane" people.
{ note: It is pretty much accepted the Stirling engine concept is not fit for automobile engines. Heat exchangers can be as simple as solid materials that don't move. Fuel economy may not be an issue when the advantages of using unlimited but unusual fuel sources that a Stirling engine can make use of. }
{ note: It is assumed Stirling engines are used as constant run, constant speed engines. "Kick Starting" a Stirling engine shouldn't be an issue. }
{ note: again, Stirling engines are meant for constant use, constant speed industrial uses. Variable speed Stirling engines can be considered an optional enhancement. }
{ note: For very small Stirling engines for individual use, this may be true. The answer is simply to not use Hydrogen. Stirling engines run on most gases, including ordinary air. Hydrogen is the best working gas, and a very tiny rate of loss through the walls of the metal itself or through the seals becomes less important with the increased scale of the system. A large Stirling engine, used to manufacture commercial electricity to produce hydrogen as a product to be sold, for use in hydrogen cars, can use a feedback system with an extremely minute amount of hydrogen required to return to the system. }
Good. Though there coud be something in all of this, it goes in so many directions at once that it is not coherent. The constant-speed matter is already covered in the article. -Will Beback08:29, 15 May 2006 (UTC)
Cryocoolers and heat pumps
The section Sterling Cryocoolers could use some work... it isn't clear to which parts of the machine are being referrer, or exactly what is being claimed about them. The English is also awkward... missing articles, punctuation, etc. Unsigned Posted by User:24.62.250.91
I have improved the English in this description. I think Cryocoolers and heat pumps should really have their own article, see "Topic" section above . Lumos311:45, 10 November 2006 (UTC)
Heat pump has an article; Cryocooler is a page that can't decide if its a stub or a disambiguation page. Please, feel free to be bold and improve any of these pages!
"Notably, some are in hot pursuit of the rotary Stirling engine; the goal is to convert power from the Stirling cycle directly into torque, a similar goal to that of the design of the rotary combustion engine."
This implies that rotary Stirlings don't exist yet, which isn't true. http://www.rotarystirlingengines.com/index.htm's history section documents several, but they vary so much in design that I don't know how to add them into the Configurations section.
This is a major problem with this article, i.e. the apparent POV that Stirling engines use only pistons. The Stirling cycle can use a number of different mechanical configurations besides pistons (though at present it is the most well known and common form). The differentiation needs to be made between the 'Stirling cycle' and the 'Stirling engine' which this article fails to do. While 'Stirling cycle' redirects to this article, they may be worthy of two different articles. Either way, this article needs a lot of work Nodekeeper17:38, 10 September 2006 (UTC)
If you want, make a section just on the cycle. If it grows to contain enough content independent of the rest of the page, it can be spun off into its own page. Tom HarrisonTalk17:45, 10 September 2006 (UTC)
Rotary stirlings are not in service they are patents and models, so they dont need to have equal space to the main article. It would be good to see a section on them though. Lumos320:02, 10 September 2006 (UTC)
Hydrogen vs helium
somebody made a comment about the danger of hydrogen being dangerous. since the gas inside a sterling engine is sealed inside a machine, i suppose it would be a reasonable risk, certainly less dangerous than say a hydrogen internal combustion engine. helium is certainly safer and the expansion / heat properties are close enough.
but if/when sterling engines break out and become wildly popular, in many parts of the world, helium may not be readily available. hydrogen can be manufactured by a simple process using electricity and water. a sterling engine used to drive an electrical generator would then be able to have a tiny feedback process to create replacement hydrogen for the small amount that would leak with all but unnoticeable efficiency loss.
so, there may indeed be a future market for hydrogen based sterling engines.
I made an animation of the 4 images showing the action of a stirling engine. It's not great. I probably should have made the timing on it longer so it doesn't look so jumpy. Let me know what you think. --SuperCow23:07, 5 November 2006 (UTC)
That's pretty nice. If we could somehow let readers 'click here to animate this image' and click again to stop, that might be good. I don't know offhand how to do that. Tom HarrisonTalk00:02, 6 November 2006 (UTC)
Could you make it so that the cylinder itself does not vibrate? Lumos3
Well, I just stuck those 4 images into a .gif file. To make it so that the cylinder doesn't vibrate, all 4 pictures would just have to be redrawn so that they matched. I can't think of any other way of making it not jumpy. --SuperCow17:16, 10 November 2006 (UTC)
One of the images is a bit big; scale it down. Move the other layers so they overlap properly (make them 50-80% transparent in GIMP so you can see wtf you're doing), then line that one up. Fit all the layers to canvas size. Save. I'll leave doing it up to you; you'll learn something. --John Moser23:27, 13 December 2006 (UTC)
Alright, I tried to make it better. Let me know what you think. Still learning how to use GIMP, thanks for the input everyone, especially John Moser. --SuperCow21:07, 17 January 2007 (UTC)
Nice work. I think it looks even better at 100px . Could you add some intermediate frames so that it runs less jerkily. Lumos310:38, 24 January 2007 (UTC)
Wikibooks has a [[1]] book. Add a Stirling cycle engine section to this and do one of the can type, and maybe a metal lathed one. I'd like to build a few myself to test out. --John Moser23:31, 13 December 2006 (UTC)
Do we have any support for the claim of 50%-80% efficiency? That figure seems very high compared to the other values that I've seen for actual engines. Is the figure based on the theoretical maximum? If so, perhaps we should mention that.
The very opening of the article makes the following claim:
In the conversion of heat into mechanical work, the Stirling engine has the potential to achieve the highest efficiency of any real heat engine, theoretically up to the full Carnot efficiency, though in practice this is limited by non-ideal properties of the working gas and engine materials, such as friction, thermal conductivity, tensile strength, creep, melting point, etc.
I thought I would check this so I calculated the efficiency of the ideal cycle and I got the following results:
for the low temp isotherm the heat transfered out Q = NkTlln(Vh/Vs),
for the low volume isometric step I get the following absorbed: Q = aNk(Th - Tl),
for the high temp isotherm the heat absorbed is: Q = NkThln(Vh/Vs), and
for the high volume isometric step I get the following heat expelled: Q = aNk(Th - Tl).
Naturally, I drop these into the equation for efficiency: e = 1 - Qc/Qh and I get: e = 1 - (ln(r) + a( T - 1))/(T ln(r) + a(T - 1)), where r is the compression ratio, T is the ratio of the high temperature reservoir to the low temperature one, and a is the constant volume heat capacity divided by Nk.
It is obvious that if it weren't for the isometric heat transfer terms then the efficiency would be carnot. The most obvious solution would be to use a really high compression ratio to overwhelm the isometric terms, but that is really hard since the compression ration is inside of a logarithm. The other option is to find ways to reduce the heat transfer during the isometric part of the cycle, attempting to make them more like the adiabats in Carnot's cycle. The question I have is how much toward that goal can a regenerator really get you?
I have annotated the cut away diagram of a beta type engine and moved this to the head of the article. This has greater explanatory power than the generator set image previously there. I have moved the generator set to juxtapose it to the photo of the desktop engine to show the range in size and power output of the Stirling engine. Lumos310:20, 22 February 2007 (UTC)
Action of an Alpha type Stirling engine
1. Most of the working gas is in contact with the hot cylinder walls , it has been heated and expansion has pushed the hot piston to the top of the cylinder. Expansion continues in the cold cylinder piston, which is 90o behind the hot piston in its cycle, extracting still more work from the hot gas.
2. The gas is now at its maximum volume. The hot cylinder piston begins to move most of the gas into the cold cylinder , where it cools and the pressure drops.
Animated version.
3. Almost all the gas is now in the cold cylinder and cooling continues. The cold piston, powered by flywheel momentum or other piston pairs on the same shaft, compresses the remaining part of the gas.
4. The gas reaches its minimum volume and the hot cylinder piston will now allow it to expand in the hot cylinder where it will be heated once more and drive the hot piston in its power stroke.
Would someone who knows what they are talking about mind filling in an explanation for each step? :) The images may get improved at some point (to show changes in temp/pressure) but I think its time for me to go to bed! - ZephyrisTalk00:49, 23 February 2007 (UTC)
Again nice work here Zephyris. However you need to show a regenerator in the pipe which is a key componant of the Stirling engine. The animated diagram here shows how it works. http://www.keveney.com/Vstirling.html Its the green box midway along the pipe.
I am against showing the Stirling cycle adjacent to one of the engine designs as it is a general concept which applies to all designs. Lumos300:30, 26 February 2007 (UTC)
It was not intended to be one of the engine designs - it is an idealised design - although it is based on the alpha for clarity... - ZephyrisTalk16:40, 26 February 2007 (UTC)
