Nasa "free piston" displacer in combination with crankshaft?

[Tom Booth]

I had to watch the video again.

Now I honestly just don't know, or can't decide. There are too many unknowns about this engine. Maybe there are some clues in the description or comments.

I don't know how close the tolerance is in the cylinder. Possibly the pressure of pushing the power diaphragm down, creates enough pressure ABOVE the displacer to force it down, temporarily.

You may be right, but if that little bit of pressure is enough to generate that much heat inside the displacer that quickly, I'd find that rather astonishing, especially with a hole in the can.

Does this contraption even run? Anyway you've got me wondering now.

I'm intending to build a similar transparent "NASA" engine and take some video and run it in slow motion.

This doesn't look to me like a REAL functional engine. It certainly isn't actually running.

A few things to possibly consider or try.

Would the same thing happen with the little vent hole taped shut? What is the clearance around the displacer? It looks aluminum, is that important? Rapid heat transfer?

Again though, if pushing the power piston down creates enough heat to transfer through the aluminium, heat up the air inside the displacer enough to cause it to expand, well, wouldn't the air outside the can get hot and expand first, pushing the displacer diaphragm down, or pushing it in?

I still think the pressure above the displacer forces it down, but the balloon is attached to that metal, so it is stretched out, not pushed out by internal heating of the displacer can. That doesn't really seem possible to me at this point.

I still have to conclude the displacer is just responding to the air pressure being created above it and moving down, making it look like the balloon is expanding.

But now I need to do some more research and watch that video a few more times, check out the comments, etc.

[Tom Booth]

It does run!


https://youtu.be/Pqe1HyZRbHI

The gap is quite small. Maybe 50 or 60 thousandth of an inch. And with the rubber on top and a rubber band holding it on, I would assume less than that.

With such a close fitting displacer I'm more convinced the displacer is likely just going down with the piston (power diaphragm) from air pressure. Still not 100% certain though.

I can't find much of any clear explaination in the description or comments on YouTube.

[ccspring3021]

Hi Tom,

As you know, any displacer will not work as a piston, so I think it will not be the difference of pressure between up and down.
And from the former video when the user press the piston manually, you can see there is a delay between the piston and displacer moving. So I think the movement is not caused by pressure, which should be more immediately

[Tom Booth]

Now I'm a bit flabbergasted.

I posted that video of the engine running but didn't watch more than the beginning.

I had assumed that big heavy engine was running on the heat of the stove burner. It looked like it was sitting on an electric or gas stove top.

Then just now, watching the video again, all the way through, I see it was running on just a little tea candle.

That is a rather impressive achievement.

Watching the video with the frame rate on YouTube set to 0.25 the slowest it will go, It looks like the displacer and power piston are synced up in a way that they both come together, almost colliding, then spread apart.

If one hesitates,, they both hesitate. Kind of weird.

Some kind of oscillation going on, but just exactly how it behaves the way it does, your guess is as good as mine at this point.

That apparent regenerator attached to the power piston, it seems like a kind of odd place for a regenerator..

I guess your theory could be tested by making various displacers of different materials with different conductivity rates and see what happens.

[ccspring3021]

Hi Tom,

Yes, your idea that making various displacers of different materials can help to judge if the heat trassfer speed is the key factor that the displacer will moving after the piston.

[Tom Booth]

While looking for stainless steel and titanium water bottles for my scaled up version of my little red Stirling engine, I came across these copper water bottles.

Resize_20220218_042838_8951.jpg (207.04 KiB) Viewed 4292 times

So that's at least 3 possibilities, stainless steel, copper and titanium, though finding bottles that are all the same size might not be easy, but there is a wide variety available, so maybe not that difficult. Probably aluminium and steel are doable.

I'd also try non conducting materials; styrofoam maybe?

That might hold up under tea candle temperatures but some more heat resistant foam, perlite possibly, could be fabricated. Cardboard, balsa wood, PVC, plastic...

Could get involved, time consuming and a bit expensive, but not too bad.

Also I'd be interested in hollow vs. solid or filled, or at least not punctured.

With/without regenerator, free displacer or fixed position.

Somehow it seems like these engines find a way to run no matter how they are thrown together. There are so many different configurations of Stirling / hot air engines already it boggles the mind, but tinkerer's on YouTube and such come out with something new all the time.