Stirlingengineforum.com

Cheap desktop demonstrator, but he is using ideas I hoped to display someday. Very happy to see this idea working for someone.

Power piston is a bellows

Displacer is a rotary inside a clear housing (glass cylinder?). A magnetic bar on one end spins the displacer inside the housing. Looks like the mating parts inside are two magnets, but heat may degrade them, unless the inside elements are steel? I'm told Samarium Cobalt magnets can take high heat, but they are expensive.

Since a rotary displacer presents no back-resistance to spinning, the magnetic coupling effect does not need to be strong. I'm certain steel laminations from a transformer could be used to make a "U" shape inside the displacer housing, with neodymium magnets on the outside. Or magnets on the outside mounted to some laminations in a U shape. The two U's would want to align with each other.

I think the hose from the displacer housing to the power-bellows is too long, and could easily be made shorter to remove dead space.

The same builder has a separate video showing a practical displacer actuator with more dwell-time at both ends (https://www.youtube.com/watch?v=HRbZ6jviykw).

It works on a conventional sliding-cylinder displacer that we are all familiar with. He references another youtuber who made a similar rotary displacer, but this youtuber added the magnetic coupling to provide a seal-less design...making helium a viable gas.

https://www.youtube.com/watch?v=rcEkObqHe4Q

The configuration in your second video link is the ancient Gloy (late 1800s patent). Here's another 'spin' which I posted last year:

https://www.youtube.com/watch?v=Q3KE0OBRl6E

Your first video link is a must see for anyone pondering dwell schemes. Gadz, if Marty can help me fix my flux capacitor, I can get back to the future...

matt brown wrote: ↑Sun May 26, 2024 10:36 pm Your first video link is a must see for anyone pondering dwell schemes.

This is something I've been looking into. What's shown is a Scotch Yoke mechanism with dwell at both ends. There's also a version with dwell at one end.
What I've been looking for is if there's a formula that gives the throw and arc degree dwell dependent on the length and radius arc of the dwell segment.
Anyone ever run across a formula for this ?

The power piston is on the other side of the flywheel. The displacer is the common sliding cylinder we are all familiar with. The displacer is actualted by an elevated rocking-beam. The flywheel displacer linkage to the system has an odd-shape to increase dwell time at both ends of the stroke (hot and cold). Watch the short video to see it in action.

"...What's shown is a Scotch Yoke mechanism with dwell at both ends..."

I think that's a good description, and a great name.
Matt brown, I like the proportions with it being flatter, and more of a pancake instead of a soup-can shape. I think I'd like something about halfway between those two extremes. I've been given the impression during the "Essex" engine discussion that there is a small benefit in efficiency for the Gamma piston to draw air from the hot end. I suppose it's because when drawing air from the cold end (perhaps chosen to keep the shaft-seal cooler?), that the expanding hot air must pass through a cold section to get to the piston.

This should be easy to test, and the pancake style of rotary displacer would easily allow the power piston to be moved to any one of several places for testing purposes. I had previously envisioned a Gamma with the piston drawing its hot-air from the center of the displacer, so...the middle instead of from the hot end or cold end.