Stirlingengineforum.com

Hi all,

although I am developing my other engines further I already think about the the concept of my next big engine.

I am still undecided whether a Thermal Lag or Thermoacoustic engine is more promising for an electricity-generating system to support our solar system in times of low sunshine.

With my rhombic Stirling engines I got more than 300 watts electrical output but with a quite complex effort.

Maybe with a Thermal Lag or Thermoacoustic motor my goal of a relatively simple 500 - 1000 watts engine is easier to reach.


So that you can get an idea of my work, here is a link to a video: https://youtu.be/GJZj1azzWfk?si=HSRJYA7F3uMB9I9-


What to you think is more promising for my aims, a Thermoacoustic or Thermal Lag engine?

I would be also very grateful for any links or book recommendations of the theory and design of these engines.

Greetings

Ralf

Glad to have you here Ralph, your work is most impressive.

tom-rock wrote: ↑Sun Nov 26, 2023 4:26 am Hi all,

although I am developing my other engines further I already think about the the concept of my next big engine.

I am still undecided whether a Thermal Lag or Thermoacoustic engine is more promising for an electricity-generating system to support our solar system in times of low sunshine.

With my rhombic Stirling engines I got more than 300 watts electrical output but with a quite complex effort.

Maybe with a Thermal Lag or Thermoacoustic motor my goal of a relatively simple 500 - 1000 watts engine is easier to reach.


So that you can get an idea of my work, here is a link to a video: https://youtu.be/GJZj1azzWfk?si=HSRJYA7F3uMB9I9-


What to you think is more promising for my aims, a Thermoacoustic or Thermal Lag engine?


I would be also very grateful for any links or book recommendations of the theory and design of these engines.

Greetings

Ralf

Hi,

You have this image in your video:


There may, however, need to be some clarification regarding what the differences are between the two.

Often I've seen "thermoacoustic" type heat pumps or refrigerators that require some form of acoustic driver and so lack any kind of mechanical power output. The thermoacoustic "engine" pictured in your video appears to be of this type. (There is a "resonator tube", but no driver or piston is shown).

I haven't personally been able to work out what are the actual distinctions between thermal lag, thermoacoustic and laminar flow engines (that actually do have pistons and some mechanical power output), so the question of which might be better is difficult to say.

Which is even which?

The names seem interchangeable and are sometimes applied to engines that appear to be identical in appearance and operation.

At best the distinctions, if they exist at all are not well defined (as far as I know).

Hi all,

I haven't learned enough about thermoacoustic and thermal lag engines but as far as I know the basic principle of operation is fundamentally different.

Peter Tailer says in his US patent 5414997A:

'A thermal lag engine has a cooled cylinder and piston connected to a heated chamber.
A working fluid in the cooled cylinder and heated chamber is alternately compressed and expanded by the piston.
There is a thermal lag or time interval before the working fluid entering the hot chamber is heated and the working fluid expanding back into the cooled cylinder is cooled.'

So I think the main principle is based on this lag.
If u for example change the working fluid in a functioning engine with air to helium the lag gets much smaller and the engine refuses to run.


In the thermoacoustic variant gas dispacement must be thought of in terms of pressure waves.
Acoustic waves travel and they reflect and interact which each other.


But I still need to understand both principles in depth before i can really say anything about them.

At the moment I am studying Allan Organs new Book ('Stirling and Thermal-Lag Engines') which is going very deep into the theory not easy for a non-native speaker whose math studies were a long time ago.

About the Laminar flow engine I know nearly nothing but I will search if I can find something about its working principle.

You are right, it is difficult to find some reliable information about the working principles of the now three variants Thermoacoustic, Thermal Lag and Laminar Flow.

Nevertheless, I find the three very interesting and would really like to learn more about them and understand how they work, what potential they have and how difficult it is to optimize them.


Greetings

Ralf

There is this paper which is frequently cited as source material for "more in depth information" about thermoacoustic engines:

Swift, G. W. (1988) Thermoacoustic Engines. The Journal of The Acoustical Society of America

https://www.scribd.com/document/4474267 ... 5-1180-pdf


What I find notable from this apparently recognized authoritative source is that a characteristic of thermoacoustic engines is that they have "no moving parts".

On the topic of Stirling engines generally, and this trio of thermoacoustic thermal lag and laminar flow in particular, I see some disparity between theory of operation and reality.

I've spent more than ten years trying to understand how these various "Stirling" variants actually work, simply because I wanted to build a heat engine for power production to run off my wood burning stove or perhaps even a camp fire.

I don't really care one way or the other who turns out to be right or wrong or what the truth of the matter may be. I just want to know, factually, what actually works in practice.

With that, you have made a statement which, so far I haven't been able to find support for.

tom-rock wrote: ↑Sun Nov 26, 2023 12:33 pm
....
There is a thermal lag or time interval before the working fluid entering the hot chamber is heated and the working fluid expanding back into the cooled cylinder is cooled.'

So I think the main principle is based on this lag.
If u for example change the working fluid in a functioning engine with air to helium the lag gets much smaller and the engine refuses to run.
...

Not trying to put you on the spot, but in researching this, what I have found so far seems to contradict this, i.e. a Thermal Lag engine charged with helium will refuse to run.

This paper for example:

https://www.mdpi.com/1996-1073/15/20/7688

Titled: Modeling of Thermal-Lag Engine with Validation by Experimental Data

Statements are made in the paper to the effect that the engines being studied show an increase in power output when helium or hydrogen are used as the working fluid.

I confess I have not read the paper thoroughly as yet, but from the title I would tentatively assume the statements are backed up by experiment.

Be that as it may, I am curious to know the basis or source of information for what was stated above, that changing the working fluid to helium alters the "lag" in such a way that a thermal lag engine will refuse to run.

Is this something you've seen in your own experiments, something you read or what?

Possibly the authors of this paper are generalizing and haven't actually used helium in their test engine, I don't really know at this point.

One would think that Peter Tailer would know how his own invention actually works, but sometimes inventors jump to conclusions or make false assumptions or just have a theory that is not necessarily fact.

From what I've read, a working "thermal lag" engine was arrived at through trial and error.

Another paper states specifically:

"It is shown that the minimum entropy generation is recorded when using helium as working fluid. For this small engine, helium has more advantages than air and
nitrogen. This is due to low pressure drop and high specific heat of the helium. In fact, the thermal lag Stirling engine has less loss when using helium as the working gas."

PDF reference:

https://uphf.hal.science/hal-03436504/document

Hi,

thank you very much for the well-founded contributions and interesting documents.

One of the most powerful research thermal lag motors I have seen so far is the one from Geoff Vaizey.
His engine stopped when he used helium instead of air and the simulation by Allan Organ, which was validated with this engine, came to the same result.

I made the mistake of concluding that this is always the case.
But it doesn't seem to be.

As I said, I am still familiarizing myself with the subject.

Now I have much to read before I can write more.

I hope the fruitful discussion continues, as soon as I have something interesting to report I will do so and hopefully you will too.

Greetings
Ralf

tom-rock wrote: ↑Mon Nov 27, 2023 12:42 pm Hi,

thank you very much for the well-founded contributions and interesting documents.

One of the most powerful research thermal lag motors I have seen so far is the one from Geoff Vaizey.
His engine stopped when he used helium instead of air and the simulation by Allan Organ, which was validated with this engine, came to the same result.

I made the mistake of concluding that this is always the case.
But it doesn't seem to be.

As I said, I am still familiarizing myself with the subject.

Now I have much to read before I can write more.

I hope the fruitful discussion continues, as soon as I have something interesting to report I will do so and hopefully you will too.

Greetings
Ralf

These engines generally seem a bit temperamental, sometimes for not so obvious reasons.

Take this engine for example:

https://youtu.be/9OX19YRY9fM?si=OFqIZpR4yiww0AWq

I was experimenting with various non-flammable liquid lubricants. This engine had previously been lubricated with graphite only.

Liquid lubricant on the piston brought the engine to an immediate halt.

I tried all kinds of things to get it running but nothing worked.

The engine though, had an unusually long tight fitting glass piston and I thought that maybe the higher viscosity of a liquid lubricant was creating excessive "drag" so I shortened the piston and ground down the diameter leaving only a couple thin rings to form a seal.

After that modification, though the engines compression increased tremendously with the liquid lubricant, this did not deter the engine which now ran better than ever and with considerably more torque.


https://youtu.be/Opzd0yxWq98?si=e2W5XgQdJj6hsk7A


https://youtu.be/D6F_cDjrEEU?si=JIK1ahRLm6WR7TsS


I could have simply given up when the engine refused to run, blaming it on the liquid lubricant saying that Stirling engines cannot run with liquid lube or with too high compression or something.

Needless to say, with some persistence, I found that the liquid lubricant made a vast improvement in engine performance.