Stirling engine project

Discussion on Stirling or "hot air" engines (all types)
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r1ky932
Posts: 2
Joined: Mon Aug 29, 2016 10:34 am

Stirling engine project

Post by r1ky932 » Thu Sep 01, 2016 4:03 am

Hi at all,

my name is Riccardo, I'm new in this forum and I'm italian, so my english is probably not very good.

I'm trying to build a gamma stirling engine (because i've read is the "simplest"), with recycled materials, but i have a couple of question that i hope will be answered:
1) I've made the displacer entirely in aluminium, very thin and a couple of millimiters smaller than the cylinder, is it proper?
2) How can I seal up the displacer piston rod? I have to use an o-ring?

Thanks for your help in advance :big smile:

Riccardo

Wellington
Posts: 143
Joined: Mon Apr 18, 2016 4:02 am

Re: Stirling engine project

Post by Wellington » Thu Sep 01, 2016 10:09 am

Big Trev wrote:HI Riccardo - Just joined myself a few minutes ago and noticed your forum request. I have made a few with all aluminium and they work extremely well. They are light in weight and can take a fair bit of heat and your wall clearance seems OK to me, though there may be a few qualified people out there that may agree/disagree with that. As for the displacer rod I use a small O ring as you have suggested. You must make the O ring a very light fit to the rod so not to drag to much friction from your engine. Hope this helps and big Gooday from Trevor in Australia
hello trevor. Ijust posted a question on alum parts. Are you saying that its ok to make the push rod swivel, cams etc from alum and it will be durable and last years?
Wellington

Ian S C
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Location: New Zealand

Re: Stirling engine project

Post by Ian S C » Fri Sep 02, 2016 1:53 am

Aluminium is ok for the mechanical parts, but not ideal for the displacer for a number of reasons. First it conducts heat too fast from the hot end, to the cold end. Next if you are going to use anything hotter than a candle, or small meths burner, it won't stand the heat.
Ian S C
Last edited by Ian S C on Tue Sep 06, 2016 2:14 am, edited 1 time in total.

Wellington
Posts: 143
Joined: Mon Apr 18, 2016 4:02 am

Re: Stirling engine project

Post by Wellington » Fri Sep 02, 2016 9:19 am

Ian S C wrote:Aluminium is ok for the mechanical parts, but not ideal for the displacer for a number of reasons. First it conducts heat too fast from the hot end, to the cold end. Next if you are going to use anything hotter than a candle, or small meths burner, it won't stand the heat.
Ian S C
DSC01133 (800x600).jpg
yep, ive heard others say the same thing about alum melting eventually with a short life. so if not an alum displacer and not wanting to use fragile glass, what is the next best option for a durable displacer that is lightweight? I'm currently looking at two steel washers on a rod with steel wool filling but if you know a better option other than turning a solid block of graphite please let us know.
regards
Wellington

Alfista
Posts: 91
Joined: Thu Feb 18, 2016 9:14 pm

Re: Stirling engine project

Post by Alfista » Fri Sep 02, 2016 8:11 pm


I have made several displacers out of aluminum. None have melted or developed problems. There are several good methods for making a displacer. Ian is right to point out the potential problems and inherent disadvantages of aluminum. That said, aluminum is very light and whereas it may be quite easy to burn through a thickness of .003" (a typical soda can), if we increase that thickness to .010, then the material is substantially stronger and safer. To some extent it is also dependant on the firing method and how hot the workng temperature must be. A thickness of .062", not exposed directly to a flame, I.e. within the displacer cylinder, will withstand a great deal of heat before melting or warping. Although it is never a good idea to leave an engine on full heat without the engine moving, especially with the displacer fully extended towards the hot cap. It is just asking for trouble.
I recognize the superior thermal qualities of stainless steel but I HATE machining it ! I am perfectly happy with the compromise of using aluminum and many successful engines have been made with aluminum displacers.

Ian S C
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Location: New Zealand

Re: Stirling engine project

Post by Ian S C » Sat Sep 03, 2016 3:31 am

Thin walled stainless steel, or slightly thicker mild steel are what I use, for smaller motors I have used the steel case from AA size NiCad batteries for either the hot cap, or the displacer. Just make sure it's a dead battery before you start digging the stuff from inside. Ian S C
Last edited by Ian S C on Sun Sep 04, 2016 3:31 am, edited 2 times in total.

Wellington
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Joined: Mon Apr 18, 2016 4:02 am

Re: Stirling engine project

Post by Wellington » Sat Sep 03, 2016 10:21 am

I prefer to use unobtainium for its lightweight and stronger than steel qualities for a displacer
Wellington.

r1ky932
Posts: 2
Joined: Mon Aug 29, 2016 10:34 am

Re: Stirling engine project

Post by r1ky932 » Sun Sep 04, 2016 8:59 am

Thanks for all suggestions, my project was meant to be used with a candle or a small heater. This project is only for fun, so i don't need something very efficient.

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

Re: Stirling engine project

Post by Ian S C » Wed Sep 07, 2016 4:45 am

Here is the effect of heat on aluminium displacers.
Ian S C
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DSC01133 (800x600).jpg
DSC01133 (800x600).jpg (170.21 KiB) Viewed 4999 times
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