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Lamina Type Hot Air Engine Antics

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I tried one similar, Elmer Verberg's from memory. I differed in that the tube contained a few glass marbles. Other members of my club got them to run, I alas failed completely so turned it into an air engine with a piston? type valve on a cam - that worked at least.

Anyway, have you tried with your spirit lamp out at the end of the tube? I ask because that seemed to  be the position in the glass ball version. Nothing to lose by trying.
All the best for 2022,
John B

Yes John, thanks!  :beer: I have tried it at the end of the tube in all of the above mentioned configurations.

I'm thinking about the small size of the piston and small stroke, and resultant low compression ratio.

I might try increasing it by putting a piece of solid rod in the test tube end, reducing its volume.

You may be able to reduce friction by washing the oil out of the bearings.
I vaguely recall reading the oil introduces drag.


Russ, thanks,  :beer: I've tried it both ways so far, dry and lightly oiled (Singer sewing machine oil). Still no go.

Piston seal is better with oil and when I flip the flywheel I get more revolutions with oil before the wheel comes to rest. That says to me that at low revs, at least, oil reduces friction in this particular engine. If it actually ran, but slowly, then maybe we'd suspect that the added viscosity of oil might be limiting the top speed. But it won't even turn one complete revolution under its own power.

The dry aluminum piston in an aluminum cylinder is not a good bearing pair. Dissimilar metals would be better (with the exception of cast iron pairs), eg. graphite in a bronze or cast iron cylinder would be lower friction. An aluminum cylinder does however sink more heat at the cold end. And the low mass of an aluminum piston is considered an advantage so, well, everything is a compromise one way or another.

BTW in this engine there is no danger of carbonizing oil in the power cylinder (as there is in a conventional high performance displacer type engine) since the temps are relatively low, and the cylinder is finned.

I tried reducing the test tube volume, and thereby increasing the compression ratio, by putting a 5/16" x 2.5" steel rod inside, along with some of the stainless wool from before, but still no go.

Next possibility, I noticed that some of the runners on YT  have what looks like a nozzle restriction between the test tube and the power cylinder.

In this engine, the power cylinder is the same bore as the test tube. I might try adding a thin shim orifice behind the test tube junction.


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