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After building several high power (up to 300 watts) kinematic Stirling engines and struggling much with wear and friction which makes them very maintenance intensive I want to try new concepts.

Now I will give the Thermoacoustic Stirling engine a try and I am very curious about its potential as there is very limited information about it, specially about builds by hobbyists.

So that you can get an idea of the engine, I have linked a video of my thermoacoustic engine here:

https://youtu.be/kJVnSkKGb3E?feature=shared


If you don't know much about thermoacoustic Stirling engines I give here an introduction:

https://youtu.be/GpqqAzYAOh0?feature=shared


What do you think of the thermoacoustic Stirling engine in general and also my attempt on it?

Do you have any suggestions or information for me?

I would be very happy to get some feedback!

Greetings

Ralf

Dear Tom-rock/Ralf, welcome!

I have seen your videos before, and they are impressive. I have not studied these yet, but I must admit that they are intriguing. I had decided that your channel is one that I will keep an eye on, to see what you discover about making a practical Thermoacoustic engine.

I am very pleased for you to be posting here, and sharing the information you discover through your experiments.

Looks impressive! I wish I had a workshop like that.

I'm mostly wondering about the advisability of using copper fittings.

I'm no expert on thermoacoustic heat engines, but for Stirling engines generally, other than for an actual heat exchanger, I try to avoid metal if possible and copper and aluminum in particular.

Over the years there have been several instances of people dropping in on the forum asking why their engine doesn't work. I can recall a few instances where I had strong suspicions the problem was the use of copper tubing.

Unless the copper elbows etc. are intended as cold heat exchangers, perhaps PVC pipe would give better heat retention.

@ Jack and spinningmagnets: Thanks, for your kind post!

If you want to have a workshop like mine just build it, it is really nice to to have the possibility to machine what ever you want!
It was not expensive (my wife would never allow that ;-) ) everything is bought used and cheap and electronics (if you need CNC, I am too lazy to crank) are ridiculous inexpensive nowadays!

@Tom:

To keep the hot temperature in the heater zone I use the pyrex test tube which has a very low conductivity.

On both ends of the glass tube are coolers (and before the main cooler also the regenerator or "stack" in this case) so I hope that thermal conductivity losses are not too high.

This engine is just a prototype engine not intended to have a high efficiency, surely an engine which has to produce useful power has to look different.

If the thermoacoustic concept seems to be suitable for me a stainless version would be preferable.

Greetings

Ralf

tom-rock wrote: ↑Sat Jun 15, 2024 9:43 am ... a stainless version would be preferable.

Agreed,

My only intention is, if it turns out the engine doesn't work with the copper fittings, I'd try something else before giving up.

BTW, have you had it running yet? It appeared from the video that construction was already complete.
What's left to do?

I just have to turn the wire mesh for the regenerator to size, set up the cooling circuit and some other small things like the mounting.

I hope to finish it to the next weekend and can begin to tune the tube lengths.

I am very curious to see if i can produce a sound from the engine.

I will report as soon as I get some results!

Excellent. Keep on exploring.

I couldn't edit my first post so I write the updated links here:

Video of my prototype engine:

https://youtu.be/cnm9v0fxKHc?feature=shared

Introduction of the Thermoacoustic Stirling engine:

https://youtu.be/0qQWjgYk5UY?feature=shared

Unfortunately, as always, everything takes a little longer.
I'm having problems with the glass tubes, which are out of round and have very different external dimensions.
They are also very fragile and I destroyed the first three because the o-ring fits were too tight for the oversized glass tubes.
Now I have ordered thinner o-rings and have to cut new glass tubes to length.

Then I can hopefully make some tests!

Now the thermoacoustic Stirling engine is running to my complete satisfaction.

Here you can see a video of it:

https://youtu.be/GXcYNeh2POc?feature=shared

The frequency is very high and the stroke is much greater than I thought!

Now I will attach some sensors and a linear generator to make serious performance comparisons to learn what improves the cycle.

If you have some suggestions about linear generators, bidirectional turbines or anything else plz let me know!

Thanks for your attention!

What would you need a bidirectional turbine for?

@ Jack: A bidirectional turbine could use the acoustic power to convert it into mechanical power to generate electricity.

The thermoacoustic Stirling engine is working now, with a very high frequency and a surprisingly great stroke (approx. 30-50 mm) of the undamped free piston.

here a Link to the video:

https://youtu.be/GXcYNeh2POc?feature=shared

I will now start to build a test stand with sensors and an linear generator to start meaningful performance comparison tests to improve the engine and learn how it can be improved.

If you have any suggestions on how a proper linear generator especially with piston damping characteristics and the possibility to start the engine (for a later closed, pressurized version) could be made or the thermoacoustic engine itself I would be very happy about your answers!

Greetings

Ralf

tom-rock wrote: ↑Fri Jul 26, 2024 1:12 pm

"If you have some suggestions about linear generators, bidirectional turbines or anything else plz let me know!"

Thanks for your attention!

Have you tried a loudspeaker as a linear generator?