# Powerfull Stirling motor ???



## ksor (Jul 14, 2010)

I want to build a "powerfull" Stirling motor !

I beleave the "power" increases with the "size" of the motor, but ...

What are the crucial points ?

How "powerfull" can I exspect a Stirling motor the size of "a shoe box" to be ?

Is there a formula to calculate the "power" of a given Stirling motor ?


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## Kermit (Jul 14, 2010)

There are formulas, but you have to 'know' a lot of design info to put into the equations.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19780016056_1978016056.pdf

Starting aroung page 108 are found several formulas for the different sterling engine configs. Its about 19Mb in size so might take a few min. to download.

Good luck with the project,
Kermit


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## Blogwitch (Jul 14, 2010)

The Japanese have a car up and running using a stirling engine, not pretty to look at but it goes, and goes well. Small stirling engines have been used for many years in the third world for pumping irrigation water, and as far as I know, even the space shuttle has Sterlings on board, used in the refrigeration side of things.

There are so many designs based on the Stirling engine principle, some more decorative or prototypical than functional. So really you need to search out the 'working for a living' designs, and try to go from there.


Bogs


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## ksouers (Jul 14, 2010)

KSor,
Ford and GM have also built engines for cars back in the 70's, as have other companies. And there are companies now producing power plants using solar powered Stirlings. So depending on the design they can be fairly powerful. But those designs are big engines and use some fairly exotic techniques to get that power.

For simplicity sake, the greater the difference in temperature between that hot and cold side the more power you will have. Also, your working fluid makes a big difference, smaller molecules work better. In the commercial motors most are using hydrogen under very high pressure (higher density) to achieve greater efficiency, but hydrogen is a very small molecule and difficult to keep contained.

From what I've seen for a "shoe box" sized engine in the home shop you can expect anywhere from a few milliwatts to about 10 watts, depending on design.


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## IronHorse (Jul 14, 2010)

Ericsson managed to get around 300HP from his engine in the 1800's, but it had a 14' diameter piston in it


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## ksor (Jul 14, 2010)

I wonder how big feet some of you have ... ;D


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## ksouers (Jul 14, 2010)

ksor  said:
			
		

> I wonder how big feet some of you have ... ;D



Well, here in the US small compact cars have been called "shoe boxes"  ;D


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## ksor (Jul 14, 2010)

Oh - that's why - communication somertimes is very difficult ! ;D


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## Dan Rowe (Jul 14, 2010)

An engine more the size you are talking about has been in production since the 1980's. I can not find the footprint but it is about the size of 2 BOOT boxes and will produce 5 shaft horsepower. For more info on the ST-5 see:
http://www.stirling-tech.com/st_engines.shtml

Dan


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## mklotz (Jul 14, 2010)

> Is there a formula to calculate the "power" of a given Stirling motor ?



I doubt that there is a formula that could, a priori, predict the power of a unbuilt design. There are just too many engineering details that can't be modeled accurately. Even if such a formula could be constructed, it would be impossibly complicated and not transferable to other engine designs. It would be useless as a tool to predict the performance of deviations from the design from which it was derived.

The best we can do is set a limit on the theoretical efficiency of a Stirling. It can never exceed the Carnot efficiency although some Stirling designs can get surprisingly close to that number.

The Carnot efficiency is given by:

eta = W/Q = (Th - Tc)/Th = 1 - Tc/Th

where:
W = work done
Q = heat input
Th = temperature of hot reservoir
Tc = temperature of cold reservoir


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## Orrin (Jul 14, 2010)

So far, pressure has only been briefly touched upon. IMHO, the easiest way to develop a high output engine would be to pressurize it. This is most easily done by having two displacer cylinders connected to a double-acting power cylinder. 

Jim Symanski did this with his Jim Dandy #6. You can find pictures of it on my Web site:

http://www.oldengine.org/members/orrin/Pic_Ctn2.htm

You can find more information about it on Dustin Symanski's Web site:

http://www.starspin.com/stirlings/jimd6.html

Many people talk about building high output hot air engines; but, Jim Symanski builds instead.

Orrin


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## Maine Ronin (Jul 16, 2010)

I'm by no means an expert, I only did a little project for school on Stirling engines. From what I gather the biggest factor determining the power of a Sterling is the temperture difference between the cylinders. Not so much size. I think there's a book out there that describes a Stirling that's maybe twice the size of a shoebox that drives a generator using burning rice husks as the heat source.


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## Deanofid (Jul 16, 2010)

There was a company that made a small stirling power plant some time in the late '60s,
I think. The company was called the Phillips Company, based in Holland. The one they
made looked like a small genset and produced 200 watts. It was fairly small. Probably 
about 12"w x 18"h x 18"l. It was in production, not a concept, though not a lot of them
were made.

You might want to research that engine, and also engines developed by Andrew Ross.

Dean


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## rickharris (Jul 16, 2010)

Some information here http://roundtable.menloschool.org/issue1/umphreys/index.html

BIG stirling http://www.stirlingsouth.com/Roy/itasca2k/rob/trewhella_recovered.htm

http://www.stirlingengine.com/product?usca_p=t&product_id=49


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## Bluechip (Jul 16, 2010)

Why not ask the Swedish Navy?

They run Stirling powered submarines ..


http://www.stirlingengines.org.uk/manufact/manf/misc/subm.html

Ex Danish Navy, one of them.

Dave BC


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## matt68 (Dec 31, 2010)

I have actually tried to contact the company with regards to the ST-5, but to no avail. I don't think they are actually going to be produced as opposed to the product of a research grant. The Jim Dandy #6 looks like a great engine, but again, its a one off, and I don't get any replies from any listed emails when I inquire. I'm currently interested in building a stove from scratch and incorporating a Stirling in the design to bot heat and power my shop. If anyone has any suggestions, plans, or more information on the two engines I've listed above, please let me know.


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