# Stirling Engine.



## SouthernThunder (Jun 3, 2004)

Anyone tinkered with or built a real power producing stirling engine? (1 horse or more) I've been looking to build one just to play with. Probably the beta type with a displacer piston. I was wondering what common everyday materials would be good for making the various components. I have some serious large-scale metal working tools but nothing like a little lathe or milling machine that I need. :Bawling: I understand there are ways to make them out of ballons, pop cans, etc.. but these are not capable of real power. Looking to make some usable juice here.


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## RobD (Mar 2, 2006)

Iâve built Prof. Senftâs award winning LTD (Low Temperature Differential) engine that runs on the palm of your hand. Itâs a gas at parties (No pun intended).

You really need a decent lathe to build a ârealâ Stirling. I thought about building one on the ceiling above the wood stove so that the cold attic air and the warm ceiling air would run a small alternator. A large dome sticking down from my ceiling wouldnât be a âgasâ with certain people around my house, by the way.

The guy who did a lot of experimental work on Stirling engines is Andy Ross. He has a book around somewhere.

If space is no limit (Stirlings take a lot of room per hp) you might be able to cob something together but once you start talking about displacers and more sophisticated stuff you need milling and machining abilities and equipment.

What you might try to do is take a course in your local HS or trade school. You might be able to build your Stirling there.


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## Jim-mi (May 15, 2002)

There was/is a guy that I've seen/talked with at the MREA fairs over the years...most interesting...and mostly small stuff.
Shure would be neet to see a larger application..............

Go for it


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## JAK (Oct 15, 2005)

I am interested in using stirling with a wood stove or even solar in a combined heat and power operation. The neat thing and stirling engines is you can use them yourself whereas you can't really build photovoltaic cells yourself. I would try to get at least 20% thermal-electrical efficiency, 40% thermal-hotwater efficiency, and maybe 20% leaking to heat the house and 20% up the stack. For solar-electric efficiency I would be happy with 5% same as solar panels and get 10% on top of that for hot water and 5% space heating. To get the high temperatures for running an engine you lose more heat back out the glass than if you are just space heating or hot water heating.

The advantage of a stirling engine over a steam engine is that you can use higher temperatures in your topping cycle without dealing with high pressure steam. I think it would be easier to operate safely in an automated mode for this reason. The disadvantage is that you have to use a much large engine displacement, or many small engines. The engines don't have to be built as heavy however, and it might be just as much fun for a DIY person to build 24 small cylinders and hook them all up rather than one big cylinder.

I am not sure if it would be better to use the same stirling engine for both solar and wood. A solar stirling could be located such that the hot plate faces the sun directly, but probably at a lower temperature than achievable with wood heat. A wood heated solar might be better located right in the top of a wood stove. In both cases I think the hot water tank, or preheat tank, would serve as the cold plate.

Anyhow, here is an interesting tool to figure out the size and speed and power of a stirling engine. I haven't studied all the theory yet. The heat transfer details are more complicated than a conventional steam cycle or gas turbine cycle.

Drilling down from wikipedia:
http://en.wikipedia.org/wiki/Stirling_engine
http://www.bekkoame.ne.jp/~khirata/
http://www.bekkoame.ne.jp/~khirata/academic/indexe.htm
Gets you to this page:
http://www.bekkoame.ne.jp/~khirata/academic/simple/simplee.htm

Data Input:
air pressure of 0.1 MPa (atmospheric) 
and a 500 cc engine
high temperature of 300degC on top of wood stove
low temperature of 50degC for heating hot water
Data Output:
351rpm and 18w.

Using same data and 50cc engine you get:
691rpm and 3.4w

Messing around to get 600rpm:
*80cc engine, 600rpm, 5watts *

So using a bore of 2" and a diameter of 1.75" you might fit 100 of these cylinders on top of a wood stove to get 500watts. Of course a stirling engine is more complicated than that depending whether you are an alpha, beta, or gamma kinda guy, and you would need linkages and a flywheel and some way of getting you cold plate in there also, but I think the hot water tank would sit about 12" or so above the stove top and the stirling engine cylinders would fill the space in between. It might just be a preheating tank to 20degC and the flue gases could heat it the rest of the way to 140-160degF. I think it would be easier to develop it through experimentation rather than all the theory, but the theory would give you an idea of size and speed and temperatures and power. The power and speed would give you an idea of the forces involved, which aren't all that much. I think the bottom and sides of the wood stove could be insulated with two layers on brick so that as much of the heat as possible goes into the stirling engine, and then the flue gases.

The other way to go would be to heat up you hot water first, by solar or wood, to as high as you can get, perhaps 200F, and then run the stirling engine off that, using your incoming cold water as your heat sink. The range from 40F to 200F would not get you as much efficiency or power, but you could run the engine 24 hours a day for charging batteries and just heat up the hot water discontinuously. A combination of both could work also. 

Of course it would help to have a small machine shop handy, and enjoy doing this sort of think as a hobby. I'm more of a paper and pencil and half-baked idea sort of guy myself.


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## Ross (May 9, 2002)

> I'm more of a paper and pencil and half-baked idea sort of guy myself.


You're motivational JAK, a motivational person. Its all in the spin! Great links though thanks!!


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## MN Mom (May 19, 2003)

know a guy who built a stirling engine with about a 8" displacer piston. He owns no shop tools other then a 4" grinder and a propane torch.

Believe he used a old gas can for a displacer cylinder, a soup can for displacer piston and for the power piston and cylinder he used a 4" dia copper pipe. He greased the inside of the copper pipe and put about 3" of jb weld and a I-bolt. After it set up a light tap and his piston came out. 

It runs pretty good but the light material of the gas can makes the hot/cold transfer hard.

If you coated the greased cylinder with powedered graphite it might work better (self-lubrated).

Jon


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## RobD (Mar 2, 2006)

Let's remember 1 HP = 746 Watts. 

That's a lot of Stirling!


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## JAK (Oct 15, 2005)

Yeah they don't have a lot of power, but they are efficient. I could see how they would be good for trickle charging a battery bank if they had a continuous source of temperature difference, like between a very hot hot water tank and a preheat water tank. Even 50w x 24 hours would be 1.2 Kwh and batteries charge very efficiently at that rate. I suppose you could also run it between some candles and your preheat water tank, or some sort of propane burner that could run continuously. Maybe a small well insulated bread oven that was kept at 400degF all the time so you would be heating your hot water constantly but also charging batteries constantly. If you had a small methane digester that could be the source of fuel also.


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## dcross (Aug 12, 2005)

http://www.starspin.com/stirlings/index.html

Scroll down to Jim Symanski's stirlings


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## JAK (Oct 15, 2005)

That's the best site I've seen on reasonably sized stirlings yet.


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## afrikaner (Sep 5, 2005)

JAK said:


> That's the best site I've seen on reasonably sized stirlings yet.


http://www.stirlingengines.org.uk/sun/sola4.html

There are some other as well. Google "Stirling Power Generator". I think Kokhums installed Stirling engines in their submarines as well.
http://www.stirlingengines.org.uk/manufact/manf/misc/subm.html

Great idea - I played with the idea for years, but settled on Biodiesel or hydrogen.


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## JAK (Oct 15, 2005)

That Sunpulse engine was interesting:
http://www.stirlingengines.org.uk/sun/sola5.html

Here is another small page on it:
http://www.bsrsolar.com/core1-2.php3


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