I have been trying to construct a few small stirling engines with very little succes.
One of them could barely run at very hot conditions.
I wonder how critical the size of the displacer is?
Is it possible to say anything about the relationship of the displacer and
the tube around it.
And is air leakage at the piston axis an issue?
The air pressure seems to dissapear very quickly after I move the displacer
up from the hot surface. Is it leakage or is the air simly cooling off.
I have wathed videos at youtube where the pressure stays upp as long
as the displacer is up.
This one for instance:
https://www.youtube.com/watch?v=rrlijOHQXxg
Grateful for for help and ideas.
Björn
in Sweden
New to stirling
Re: New to stirling
Air leakage anywhere, between the inside and outside of a Stirling engine is certainly a potential issue, if there is any. Ideally there should be none. In practice, a very small amount of leakage is almost impossible to avoid.
A little soapy water on the axis (or any other suspect areas like solder joints, seals, seams etc.) will usually reveal leaks. Move the displacer up and bubbles will form if there is a leak.
Re: New to stirling
When I wrote leakage at the piston axis I really meant air leakage at the
displacer shaft. I understand that leakage at the working piston is not a good idea.
In the video I attached the hole for the displacer shaft does not seem very tight
and still the pressure seems to hold for a long time.
displacer shaft. I understand that leakage at the working piston is not a good idea.
In the video I attached the hole for the displacer shaft does not seem very tight
and still the pressure seems to hold for a long time.
Re: New to stirling
It looks that way to me as well. Very rudely punched oversized hole.
In this video also, the same engine, driving a car and charging a cell phone.
https://youtu.be/dRkSI0saX88
Very unlikely IMO.
I suspect the channel, judging from numerous other perpetual motor-generator videos, may not be above faking the videos.
Re: New to stirling
Another clue, the PVC pipe appears to be completely open at the top and bottom of the central channel:
If that is actually the case, and if it were a REAL Stirling engine, these open ends would be a huge problem.
The presence of an actual small motor and just the way his "engine" runs has me suspecting the electric motor is running the engine rather than the other way around.
A real model Stirling engine would normally have a rather long, tight fitting tubular sleeve soldered on as a seal and guide for the displacer rod. Something like the tall black post in the center top of this engine:
The air has difficulty traveling through such a long tube, so that is makes a good seal, even though it may be a slightly loose fit.
There needs to be a balance between a tight seal and a too tight seal causing friction.
- Resize_20220405_193934_4749.jpg (67.75 KiB) Viewed 5094 times
If that is actually the case, and if it were a REAL Stirling engine, these open ends would be a huge problem.
The presence of an actual small motor and just the way his "engine" runs has me suspecting the electric motor is running the engine rather than the other way around.
A real model Stirling engine would normally have a rather long, tight fitting tubular sleeve soldered on as a seal and guide for the displacer rod. Something like the tall black post in the center top of this engine:
- Resize_20220405_195237_7399.jpg (127.07 KiB) Viewed 5094 times
There needs to be a balance between a tight seal and a too tight seal causing friction.
Re: New to stirling
If you go to the board index, there are free plans that include how to make a nice guide for the displacer rod from a brass bolt:
If the hole drilled out in the center of the bolt is reamed out a little, a drop of oil in the depression will ensure a perfect seal.
The more precise the fit the better, though not so tight as to cause friction.
- Resize_20220405_221932_2919.jpg (169 KiB) Viewed 5089 times
The more precise the fit the better, though not so tight as to cause friction.
Re: New to stirling
No way that gaping hole is holding air.
Unless that is sealed from underneath, or is some kind of optical illusion, I don't see how that engine could ever get going. The hole looks to be about five or six times bigger than the displacer shaft.
- Resize_20220405_225352_2839.jpg (64.99 KiB) Viewed 5087 times
Re: New to stirling
Even if the PVC pipe is plugged, there is a lot of dead air space in this design.
Re: New to stirling
I guess it's possible what looks like a big hole might actually be centering marks made with a black marker.
Either way, bottom line is, a good air tight seal around the displacer shaft IS necessary.
Either way, bottom line is, a good air tight seal around the displacer shaft IS necessary.