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Lamina Type Hot Air Engine Antics

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Maybe ten years ago I sent away overseas for a $30 Ebay Lamina type "test tube" hot air engine. This was early on, before there were dozens to choose from all over the net. The engine in the pic looked decent, but 5 weeks later, when it arrived it turned out to be somewhat smaller than imagined.  :palm:  Kinda like those offers in the back of comic books (before they became graphic novels)

Worse, it didn't run.

I messed around with it, changing out the regenerator material, repositioning it, etc, etc, but it never did run. I put several days into trying to get it to go, but finally put it on a bookshelf to gather dust.

For some reason I have just taken it down again today, and started fiddling around with it, just in case I was wrong in what I tried the first time around, and missed something. But nope. Another few hours killed today.

I mean I know I can build a working hot air engine from scratch. I have in the past. And in fact I have a much larger one in mind (and have had that one in mind ever since I started building my (and still unfinished) "new lathe". In fact that was the reason for the lathe....but that topic might best be ignored for the present)

BUT (another but), ye see, some of the questions I have about my long-planned much larger engine, might be answered by trying to figure out what I can do to get this little bit of a contraption to function as it should. I mean in fact it SHOULD work it has all the bits and pieces an engine of this type should have. Which is the reason I keep coming back to it. Because it doesn't run.

So, why, that three letter word, is the reason I'm starting this thread.

Here's the little bug:


Does it even try to turn Steve if given a helping hand?

Iím guessing friction is the issue, that displacer looks relatively heavy.

Well, Andrew, there is technically no displacer in this type of engine, just a piston.

re Friction:

The flywheel and big end of the con rod have ball bearings. I believe the small end is just pinned. When apart, I can give the flywheel a spin by hand and it sustains for quite awhile considering its tiny size and mass, and it even stops and rocks a few times because the balance is off by a tiny amount. So that seems to be pretty low bearing friction overall.

Now for the piston itself, it's 12mm dia, x 17mm L, hollowed aluminum.
Piston + con rod + bearings :  complete assembly weighs 5 grams.

Piston cylinder fit: It takes 7 seconds for the piston and conrod to drop ~ 7mm under their own weight if I hold the cylinder vertically with my thumb over the bottom end.

Here's a pic of the bits:

The only other one of those Iíve seen had a very light graphite piston which of course is a handy material in that not only is it very low friction but also can take the heat well.

An observation! I have no knowledge of these engines, and only a nodding aquaintance with the theory by which they work (or in this case, don't) The heat from the spirit lamp heats the air in the tube, which expands, driving the piston down, and the ensuing pressure drop in the cylinder causes the air to lose some of its heat to the regeneration material? If that is the case, the regeneration material needs to be right at the end of the tube where it will stay cooler, and the heat must be just enough to start and maintain the process, too much heat and it wont work as it is operating on a very slim temperature differential. Although  the op has tried it in different positions, I would move the regen material out of the hot area, and reduce the heat, and see if it works then. What was the original regen material?


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