Hello to all,
Please bare with me since I am new to this forum and having a general lack of knowledge in most things stirling.
With that said, I have some questions and would appreciate any info/assistance.
I am building a walking beam stirling engine with young nephew and was wondering about specs on gaps.
More to the point, we have a gap of about roughly 1/4 inch between the outer diameter of displacer piston and internal diameter of displacer cylinder .
Is this too much gap ? If so, what could we use to absorb heat and create a tighter seal if need be ?
This is the best fit I could find with cans.
Displacer piston gap
Re: Displacer piston gap
Hi McGyver (are you the HMEM McGyver?)
With regard to a tighter seal I think this is one of the major issues with Stirling and hot air engines generally. As small engines are pretty low power they don't have the grunt to overcome the friction that a stuffing box or traditional piston rings would create.
Take what I say with a pinch of salt as I'm only reciting what I've read (and I could have got that wrong!), my practical experience in hot air engines is virtually zero!
Regards
Paul
AFAIK the gap isn't that important but the total voume of 'dead space' is (that is, space that contributes nothing to the movement of the piston, for example if you had a long connection between the displacer chamber and the cylinder).McGyver wrote: More to the point, we have a gap of about roughly 1/4 inch between the outer diameter of displacer piston and internal diameter of displacer cylinder
Is this too much gap? If so, what could we use to absorb heat and create a tighter seal if need be ?
With regard to a tighter seal I think this is one of the major issues with Stirling and hot air engines generally. As small engines are pretty low power they don't have the grunt to overcome the friction that a stuffing box or traditional piston rings would create.
Take what I say with a pinch of salt as I'm only reciting what I've read (and I could have got that wrong!), my practical experience in hot air engines is virtually zero!
Regards
Paul
I would say that the gap has to be within a certain range, but I don't have any exact specs cause I don't know. 
The reason I say this is that if the gap is too large, there would be no reason for the displacer piston to move?
If the piston were 2" in diameter and the cylinder walls were 4 inches, that would be way too much, IMO.
I think you need to say how big your cylinder and displacer is to get a good idea.
I have about 1/8" gap around my piston on a 4" cylinder and it runs great.
I got lucky just because of the cans I used.
Note that my first Stirling is still not running
Here's info on Stirling #2.
http://www.el34world.com/Misc/Stirling/stirling3.htm
The reason I say this is that if the gap is too large, there would be no reason for the displacer piston to move?
If the piston were 2" in diameter and the cylinder walls were 4 inches, that would be way too much, IMO.
I think you need to say how big your cylinder and displacer is to get a good idea.
I have about 1/8" gap around my piston on a 4" cylinder and it runs great.
I got lucky just because of the cans I used.
Note that my first Stirling is still not running
Here's info on Stirling #2.
http://www.el34world.com/Misc/Stirling/stirling3.htm
Question, EL34....
I noticed a nut, bolted on top left of displacer housing of can in photo.
Can you describe the reason for it ?
I want to pitch an idea at you and see what your opinion is as well...
If I were to use a beer can as the displacer piston in the displacer cylinder, would the thin metal be a problem ?
Also hoping the can would be light enough to generate a faster cycle rate than a fruit or soup can.
I noticed a nut, bolted on top left of displacer housing of can in photo.
Can you describe the reason for it ?
I want to pitch an idea at you and see what your opinion is as well...
If I were to use a beer can as the displacer piston in the displacer cylinder, would the thin metal be a problem ?
Also hoping the can would be light enough to generate a faster cycle rate than a fruit or soup can.
I added a 3/4" wide brass strip inside the cylinder. That way I had something more substantial to solder the brass tubes to. The nut is just securing one end of the brass strip to the can. I used the red high temp silicon to seal the underside where the nut and tubes come through the can.
Beer can would be great cause it's real light.
You can't solder to it cause it's aluminum, so you just have to figure out how to seal the piston air tight and make a solid rod connection that does not come loose from movement or the high heat inside the cylinder.
Beer can would be great cause it's real light.
You can't solder to it cause it's aluminum, so you just have to figure out how to seal the piston air tight and make a solid rod connection that does not come loose from movement or the high heat inside the cylinder.