Twin LTD Stirling problems (and solutions)

[Tom Booth]

One of my Twin LTD Stirling engines arrived today.

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A nice looking engine, but I tried it out on a cup of hot water and it seemed to run very poorly. Hot water straight out of the tea kettle and I could hardly get it to run, or keep it running much for long at all.

Looking it over for a while I noticed what I believe may be the problem, or rather problemS

For some reason, or perhaps no good reason I can imagine, the opening to the power cylinder is very restricted, there is some kind of little brass orifice in the bottom of the power cylinder. The opening looks to be no bigger than a #2 pencil lead.

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What on earth could be the idea behind that?

An additional related problem, which I've encountered before in these types of small LTD engines is the Displacer is set so high that it buts up tight against the top metal plate of the engine, while leaving a big gap at the bottom.

The problem with the Displacer being set high like that is, as if it wasn't bad enough that the power cylinder opening is so ridiculously small, it becomes completely blocked off during much of the power stroke when the air is supposed to be expanding and pushing the piston.

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That's the same camera angle as before but now the displacer has completely covered up the already tiny opening to the power cylinder.

This may not be easy to fix as there are no adjustments. I will likely have to replace the connecting rods with longer ones.

[Tom Booth]

Yes, the hole in the bottom of the power cylinder really is that small.

I don't know yet what holds that brass piece in place, so I'm hesitant about just drilling it out.

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Just glued on.

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[Tom Booth]

Yikes, incredibly, the foam rubber spongy displacers press up tight against the displacer chamber ceiling for at least 45° more like 90° EACH, and they alternate.

So for anywhere between 90° to 180° of the engines flywheel rotation there is resistance and power lost to just compressing the spongy displacers against the chamber ceilings and blocking the air flow to the cylinders.

The connecting rods need to be about 1/8" longer than they are. There seems to be no way to remedy this other than to make new connecting rods.

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[Tom Booth]

So a tiny airway blocked by foam. not a way to get a lot of power to the piston, i don't think.

As it turns out, the displacer is press fit onto the connecting rod, so it would have been possible, perhaps, to just pull up (hard, as it is a tight fit) on the connecting rod to have the displaer slide down a bit, without taking the engine apart, but to late for that in my case.

The displacers are also very porous. Perhaps it is intended for them to act as regenerators. I don't know if this black plastic foam stuff could make an effective regenerator. Maybe.

I think I have figured out a way to have one side of the engine act as a heat engine while the other side acts as a heat pump, but it will require quite a bit of retooling and reconstruction, but is, at least, I think, mechanically possible.

Currently, I'm setting up a new bigger/better workshop, so it may take some time before i go much further on this project.

[Tom Booth]

Just an observation; I noticed in this video, the Kontax twin Stirling seems to not have the problems I'm going to need to set up a machine shop to correct in the less expensive models I purchased.

The cylinders, have large, full size openings (as they should, as a matter of common sense I would think) and are threaded with neoprene gaskets (rather than simply glued on)

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The above screenshot was taken from this video.

https://youtu.be/BRB0pnb_JqY

The Kontax engines are perhaps, too well made to subject to tearing down, hacking apart and generally demolishing for my crazy experiments, but they probably would have been well worth the extra money.