Alpha Stirling Engine Project

Discussion on Stirling or "hot air" engines (all types)
Aviator168
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Joined: Tue Feb 08, 2011 2:29 pm
Location: Brokeville, NY. USA

Re: Alpha Stirling Engine Project

Post by Aviator168 » Mon Mar 23, 2015 10:11 am

I see the cold piston sticking out. Why is that?

Ian S C
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Location: New Zealand

Re: Alpha Stirling Engine Project

Post by Ian S C » Thu Mar 26, 2015 12:46 am

Conner, you could try thinning the hot cylinder, at the hot end to say 1 mm to 1.5 mm thick, the thinner it is the easier it is to heat the air inside.
Ian S C

Connor
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Joined: Mon Mar 16, 2015 10:49 am

Re: Alpha Stirling Engine Project

Post by Connor » Fri Mar 27, 2015 2:11 am

Aviator168 wrote:I see the cold piston sticking out. Why is that?
The Pistons are just shorter than the cylinders, so each one sticks out by 15-20mm at the end of each stroke. I did this to encourage air seal, but I may halve both their lengths in attempt to reduce friction/weight. They're currently about 57mm each.

Connor
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Joined: Mon Mar 16, 2015 10:49 am

Re: Alpha Stirling Engine Project

Post by Connor » Fri Mar 27, 2015 2:12 am

Ian S C wrote:Conner, you could try thinning the hot cylinder, at the hot end to say 1 mm to 1.5 mm thick, the thinner it is the easier it is to heat the air inside.
Ian S C
Thanks Ian, I'll give this a go.

vamoose
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Joined: Tue Jul 03, 2012 12:16 am
Location: Australia

Re: Alpha Stirling Engine Project

Post by vamoose » Sat Mar 28, 2015 9:39 pm

Hey Connor,

Here's a few suggestions that might be worth considering..

A regenerator might be worth trying. You could fill your tube with material from a s/steel scourer pad, maybe the first clear tube would allow a good fill factor without choking airflow too much.

Experiment with the phase angle, some alpha engines will run better with a phase angle of up to 120 deg, so somewhere from 60 to120 might give you a better output for your particular engine. Play around you never know??

Place a shroud/flue around the hot end to allow the hot gas from your flame to better fully envelop
the cylinder and input more energy/heat.

Use a hotter burning heat source.

Try different lubricant viscosities, and/or lubricant types, have you considered ptfe based lubricants they can have good stability at high temperatures, also maybe your hot and cold side lubricants could be different to each other depending on their operating characteristic requirements.

increase surface area on the cooling side. Maybe place some much larger cooling fins on with thermal glue/paste, or even better braise them on

increase hot side surface area by machining in grooves to the outside of the cylinder

also for interests sake see if it improves with a wet cold cloth wrapped around the cooling side

good luck
vamoose
Last edited by vamoose on Mon Mar 30, 2015 2:44 am, edited 1 time in total.

Ian S C
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Location: New Zealand

Re: Alpha Stirling Engine Project

Post by Ian S C » Sun Mar 29, 2015 1:48 am

A good lubricant is the synthetic oil used in aviation gas turbines, if you have an airstrip near by with a maintenance depot, you might be able to scroung a few ml.
Ian S C

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

Re: Alpha Stirling Engine Project

Post by MisterQED » Fri May 29, 2015 12:34 pm

I'm a nube, but I think I've developed some book knowledge, so let me try...
Tough to get a sense of scale, but you are looking for a volumetric change relatively similar to the absolute temperature change. http://www.solarheatengines.com/2009/11 ... tor-guide/ So depending on how you computed the displacement of the engine, I think your compression is still a little low due to the volume of the copper pipe. It also doesn't seem like you have a proper regenerator other than the copper tube, so I'd suggest filling part of the copper transfer tube with iron wire or something similar. This would seem reasonably easy, cheap and will raise the compression ratio and give you a better regenerator. I doubt you would be able to plug the pipe, so even if this is a dumb idea, it will be easy to reverse if incorrect.

Ian S C
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Location: New Zealand

Re: Alpha Stirling Engine Project

Post by Ian S C » Sat May 30, 2015 4:12 am

Mister QED, at least as important in this design would be to replace the copper tube with steel(steel brake tube), this would reduce the heat conduction from the hot cylinder to cold. The outsige of this could have cooling fins similar to those on the transfer tubes between cylinders on multy cylinder compressors.
Ian S C

Crazyguy
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Joined: Sun Jun 07, 2015 10:39 am
Location: USA

Re: Alpha Stirling Engine Project

Post by Crazyguy » Sun Jun 07, 2015 10:51 am

Hello
Im new to Stirling's and have never built one. I have a idea for an alpha stirling.
I want to use DIAPHRAGMS INSTEAD of PISTONS. I want to put the cold cylinder in a pond and the hot cylinder in a solar trough collector. The question I have is , the pipe that connects the two cylinders has the regenerator, can this be long? Is there a limit to the length?

Ian S C
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Location: New Zealand

Re: Alpha Stirling Engine Project

Post by Ian S C » Mon Jun 08, 2015 4:47 am

It can't be very long, it joins the hot and cold cylinders via the shortest route, a longer tube is just waist space.
Ian S C

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