Stirlingengineforum.com

To make a long story short, my roomate had a school project where he had to make a stirling engine and it didn’t go do well. So now he’s left for christmas and I want to build a working one because ive been inspired. I’ve read a ton about them, and decided to give it a shot. So i went to Home Depot and got started.

The construction is something like this:

copper tubes with caps sealed with JB weld

Holes towards the back of the tubes linked with refrigerator copper tubing sealed with JB weld.

Piston made with epoxy putty hardened in the tube to make a perfect seal, then removed, very lightly sanded and lubricated to have very little friction but a good seal.

Crankshaft is made of an old coat hanger bent to make the correct angles.

connecting rod is connected with thinner stainless steel wire wrapped loosely around a link in the piston and the crankshaft.

the weight is made from washers JB welded together and then balances with a clip of coat hangers to spin perfectly.

on one iteration i had a regenerator, there is not one on this.

Everything works exactly as i would imagine in my head. very low friction, good sealing (i can tell because when the pistons are disconnected from the crankshaft i can move them by just moving one and not touching the other). So I have to believe i must have something conceptually wrong. I feel like i definitely have the crankshaft throws going the right ways but maybe i could be wrong. At this point I feel that maybe the compression ratio is too high and I need to shallow out the throws of the crankshaft, or the pistons are too long giving extra friction. When I spin it by hand it doesn’t really want to go at all. Does anyone have any advice? Another roommate had suggested that maybe the thermal expansion of the copper tube was allowing blow-by on the piston, but I’m not convinced. I’m going to make another attempt, does anyone have suggestions on what to do for a redesign? I want to keep the same style, copper tubing alpha design, but i’m open to pretty sweeping changes.

Side note: I have done a previous iteration that had the cylinders 90 degrees to each other and the cold cylinder was up and down. It seemed more biased towards moving, but I think that might’ve just been gravity. I’ll include a picture of it as well. This one did have a very small steel wool regenerator. I’ve attached two photos of that one, and i’m pretty sure i had the throws oriented wrong on both pictures so don’t mind that, i’m not surprised that one didn’t work

Thanks!

[bbvideo] https://vimeo.com/658343280[/bbvideo]
[bbvideo] https://vimeo.com/658343138[/bbvideo]

I'm not very familiar with Alpha type Stirlings, but on observing your video, when moving the one piston manually, the other appears in the video to be barely moving. If the seals of all the joints and at the pistons were completely sound, there should be better movement of the second piston.

So, I suspect there is a leak somewhere.

Sand paper could leave scratches that might cause leaks.

I would try getting some tubing and take out one piston at a time and tape or otherwise fit the tube over the open end of the pipe and blow into the tube. Spraying some soapy water on the joints while doing this, may turn up leaks, as soap bubbles will form from the escaping air, if there is any. It should also be easy to tell if there is a leak at the other piston.

It seems obvious from the video that there is not a good air tight seal, at the time the video was made, anyway

Another potential problem might be the all-copper pipe construction. In my experience copper transmits heat very very rapidly, as I discovered one day when trying to poke a camp fire and picked up about a yard length of copper tubing, instead of the steel poker I normally used.. The heat traveled up the copper tube from the hot coals, almost instantly and burned my hand.

In other words, the whole engine may be getting almost uniformly hot, so there is not enough temperature difference between the hot and cold cylinders, the heat transmitting too rapidly through the copper tubing.