Low Temp Stirling Design - Low Weight?

Discussion on Stirling or "hot air" engines (all types)
toomey
Posts: 5
Joined: Mon Oct 05, 2015 8:04 am
Location: Moline, Illinois

Re: Low Temp Stirling Design - Low Weight?

Post by toomey » Mon Oct 12, 2015 7:01 pm

Hi again, sorry it's been so long - all kinds of busy all at once...

I saw a post somewhere on here about somebody's LTD stirling (might have been yours, Ian), about 6 inches across or so, runs on a cup of hot water. Does anyone have any thoughts about the feasibility of scaling up a design like that? Would friction and momentum be too hard to tackle? And if we were to scale it, would that be a matter of multiplying each dimension by a common factor (maintaining the ratios of cylinder bore, piston sweep, etc.), or would it be more in depth than that?

Thanks,
Matt

Ian S C
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Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Low Temp Stirling Design - Low Weight?

Post by Ian S C » Wed Oct 14, 2015 12:53 am

There is one some where on the net, probably youtube, its at least 3 foot across the displacer by about 6' high, and I think it uses 2 cylinders from lawn mower motors(instead of one very large one), it has a large but light flywheel. It is heated by the sun on the top, the bottom is in the shade so cooler. Go look for it, there is more than one video.
Ian S C

MisterQED
Posts: 10
Joined: Wed Jan 29, 2014 11:18 am

Re: Low Temp Stirling Design - Low Weight?

Post by MisterQED » Tue Oct 20, 2015 8:04 am

I would suggest you look at something like the SunPulse design. Here is a review someone posted. http://www.solarheatengines.com/2012/01 ... se-engine/
If you turn this from a single to an opposed twin you could have a lightweight and usable Stirling.

toomey
Posts: 5
Joined: Mon Oct 05, 2015 8:04 am
Location: Moline, Illinois

Re: Low Temp Stirling Design - Low Weight?

Post by toomey » Tue Nov 03, 2015 8:51 pm

Hello All,

Another update, another collection of questions...

I've attached some rough drawings of what we're doing so far (sorry, they're a little out of order)
First, Airflow: I'm worried about leaving enough volume for air to pass between the cylinders, but i don't want to leave too much.

Second, the displacer piston: I'm worried about keeping it centered in the cylinder, and I don't have room to add a support above the cylinder. How does it sound to use the shape of the piston to contact three points on the cylinder wall?

Third, Insulation: To keep the hot side hot and the cold side cold, I've opted for a ring of insulating material in the middle of the displacer cylinder. Good idea, or bad idea?


Thanks for the all the input so far, it's been a great asset!
Attachments
Gamma Stirling 05.PNG
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Gamma Stirling 03.PNG
Gamma Stirling 03.PNG (69.01 KiB) Viewed 3229 times
Gamma Stirling 02.PNG
Gamma Stirling 02.PNG (78.44 KiB) Viewed 3229 times
Gamma Stirling 01.PNG
Gamma Stirling 01.PNG (104.08 KiB) Viewed 3229 times

Ian S C
Posts: 2221
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Low Temp Stirling Design - Low Weight?

Post by Ian S C » Wed Nov 04, 2015 2:22 am

Toomey, think, low friction, don't use contact of the displacer to guide it. Where you have marked displacer piston arm clearance there should be a fairly long, well fitting bushing, say about 1", there should be minimal air leakage from there, and enough contact to keep the displacer rod stable. For the bush I'v used Carbon Impregnated Teflon, brass, bronze, and cast iron, take your pick these will all give low friction, and good service life.
Historicly, there were engines with horizontal displacers that used little wheels on the bottom side of the displacer, but these were large engine, displacer 2ft to 3ft in diameter, and made of wrought iron, and probably running at less than 100rpm.
Ian S C

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