Modified "Hot" Beta engine

[Tom Booth]

A Beta

Stirling_Animation.gif (137.66 KiB) Viewed 12103 times

OK, so here is what I'm thinking.

My reasoning and experiments over the years has led me to believe, right or wrong, that heat engines don't require cooling. At this point I no longer feel that this is just theorizing, I think I've demonstrated experimentally that it is at least possible, and in my estimation, a Stirling type heat engine often runs better without any kind of cooling jacket or sink.

Logically, to my mind anyway, a heat engine runs on heat so why should it ever be intentionally cooled? OK, Yes I know, Carnot limit and all that, the further the heat "falls" down to cold the better. So, the objective is to cool the heat engine down to absolute zero, or at least get it down as cold as possible, then heat it back up as hot as possible etc. etc.

Sounds good in theory I suppose, but is it actually true? Does it really work in practice?

Anyway, conjecture aside, I've been pondering what sort of design could be used to eliminate the cold side, and it just dawned on me a minute ago that a Beta type engine is the most like an IC engine.

On compression, both piston and displacer drive the air down to the heating chamber, then the expansion pushes the power piston out, and the displacer just kind of follows along.

The modification I'm thinking of is simply to take away the water jacket or cooling fins and instead line the power cylinder with some insulating material to retain heat.

I've avoided the Beta design generally because I don't especially like the idea of having to have a connecting rod pass through the power piston, however, if you want to eliminate the cold side and eliminate dead air space and achieve high compression, I'm not sure there is any better design.

Just have to nix the cooling and instead retain the heat for power output as much as possible.

[Jack]

It's quadruple the work and maybe a bit much for a test setup, but if you have four or more of these in a "circle" you can lead the expanded gas to the cylinder that's 90 degrees away. That way you don't have to have a moving rod through the piston, but you can connect the piston and displacer directly. Just separate the chambers.

[Jack]

So as I understand this idea you'd need to expand the air beyond its starting volume and below its starting pressure?

Do you plan to do this with a calculated stroke?
Another idea would be to use something in the same direction Vincent is building. But in stead of dwell you'd somehow disconnect the piston from the crank and let it use its momentum.
That's just a quick idea that popped up, no idea how to accomplish that though haha.

I'm interested to see what you come up with.

[Tom Booth]

It's quadruple the work and maybe a bit much for a test setup, but if you have four or more of these in a "circle" you can lead the expanded gas to the cylinder that's 90 degrees away. That way you don't have to have a moving rod through the piston, but you can connect the piston and displacer directly. Just separate the chambers.

Are you talking about this type arrangement?

Resize_20231221_121128_8519.jpg (57.2 KiB) Viewed 12075 times

https://www.beyonddiscovery.org/electro ... ngine.html

[Tom Booth]

So as I understand this idea you'd need to expand the air beyond its starting volume and below its starting pressure?

Do you plan to do this with a calculated stroke?
Another idea would be to use something in the same direction Vincent is building. But in stead of dwell you'd somehow disconnect the piston from the crank and let it use its momentum.
That's just a quick idea that popped up, no idea how to accomplish that though haha.

I'm interested to see what you come up with.

Depends what you mean by "starting" I guess.

Not really sure if there is any "normal" or standard way to build a Beta type Stirling. Compression ratio and all that, but what I have in mind is high compression, comparable to an IC engine. (Gas or diesel), an abbreviated "displacer" motion, though the "displacer" would not function as such in this case.

The "displacer" would basically serve as an insulator to control the exposure of the working fluid to the heat source.

Maybe the displacer would be better termed a "follower" or something because it would basically couple with and follow the power piston during the power stroke, then, at some point drop back down to cut off heat input as expansion continues as far as necessary to completely "use up" the heat.

Resize_20231221_124135_5991.jpg (138.94 KiB) Viewed 12066 times

Ideally, the distance that the "follower" traveled should be regulated in real time depending on the external load and rate of heat input and utilization.

Like, maybe at an Idle, the displacer would barely move. With higher power requirements the distance of "following" could be increased up to some maximum.

I was reminded of this dumb idea while reading that old thread from way back when I was ignorant about the Carnot Limit, having just learned about Stirling engines trying to figure out how they worked, using what seemed to me at the time, common sense.

Now after more than a decade of research, building model engines and experimenting, I've decided that my early ignorance was closer to reality than what's being taught in the universities as "thermodynamics".

[Tom Booth]

A drawing I posted to the forum in 2006

Resize_20231221_133106_6825.jpg (86.19 KiB) Viewed 12063 times

I had the regenerative displacer completely isolated inside an insulated bunker of sorts.

Back then I still considered external cooling to be important, though it was already nagging at me that there was something wrong about the idea of intentionally cooling a heat engine.

[Tom Booth]

Consider this experiment for example, the engine body is molded in one piece out of acrylic, except for the metal bottom for heat input

Acrylic is a very good insulator and not at all a good "sink", but just to top things off I added a silica aerogel blanket on top of the acrylic to hold in the heat.

In other words, the heat could go in through the metal on the bottom but from there, really had nowhere to go, but into "work" output.

The question was, would the engine still run?

Somewhat surprisingly it ran at a higher RPM. So fast in fact that the magnet on the power piston did not have enough time to lift the displacer. Or rather, the displacer barely lifted from the hot metal base.

The engine regulated it's own heat input according to RPM.

If the engine slowed down, the displacer lifted a little higher and a little longer. When the RPM increased the displacer barely moved.

In spite of lacking any means of external cooling there was no heat bottleneck. The engine did not overheat.
If a small load was applied, the engine would slow down slightly and the magnet would have more time to lift the displacer higher, letting in a little more heat to compensate.

Part of the video is in slow motion.

https://youtu.be/i9nz0vt7eQA?si=e57ScoHySPlPlzrU

[VincentG]

Now thats pretty cool. Maybe try to make a larger diameter foam displacer so the outer ring of the hot plate gets almost entirely covered. Should run even better like that. Maybe taller too, to bring the compression ratio up as far as it will allow.

[Tom Booth]

Now thats pretty cool. Maybe try to make a larger diameter foam displacer so the outer ring of the hot plate gets almost entirely covered. Should run even better like that. Maybe taller too, to bring the compression ratio up as far as it will allow.

I liked your idea of some heat pipe type delivery through an insulated bottom to an inside heat plate.

Surprisingly, even such a low power, low compression engine with a relatively short throw seems to be able to utilize whatever heat finds it's way inside. That was not really what I was expecting when I started these experiments. I thought I would demonstrate that with the cold side insulated the engine would not run.

How could the Carnot limit principle; that a cold "reservoir" to remove excess heat is required; be demonstrated? Maybe a heat pipe running to the engine inside a dewar bottle?

That's about the only thing I haven't tried yet.

[Jack]

Depends what you mean by "starting" I guess.

Well all engines start at a certain pressure. Be it atmospheric or pressurized.
You'd have to expand the fluid beyond that too cool it further. That's what I was getting at.

Also, I'm interested to see how all this works on something else than an LTD engine. And how much power output it actually has compared to an engine with a cold sink.

[Jack]

Thinking about it, I guess the fact that it seemed to work quite well in that video with very little lift of the displacer is promising that a smaller displacer compared to piston would work as well.

[Tom Booth]

Depends what you mean by "starting" I guess.

Well all engines start at a certain pressure. Be it atmospheric or pressurized.
You'd have to expand the fluid beyond that too cool it further. That's what I was getting at.

...

Well, I guess I don't look at it quite that way exactly.

Let's say the gas starts at 1atm. The displacer is lifted letting in heat raising the pressure to 2atm, only during and/or after that you have expansion and cooling back down to 1atm (or perchance a little less than 1atm?) And the piston returns, partly "on its own" or is driven back by atmospheric pressure and/or a flywheel.

So expansion cooling is not so much "beyond" as just back to where it started before heat was added. Start at 1atm, add heat, use up the heat for "work" output and that brings it back to 1atm.

Maybe not exactly right. Kind of a simplification. But not really anything different from what Stirling engines have already been doing all along.

I think, for the most part because engines have traditionally been made of metal that is highly conductive that the overheating problems were believed to be due to the working fluid transporting heat, since that accords with "established theory".

An engine with an entirely acrylic non-conductive engine body appears to not require external cooling or expansion "beyond" what would be considered normal.

Acrylic could not take much heat though, which is why I'm getting into high temperature ceramics. Still relatively non-heat conducting but stronger and able to withstand extremely high temperatures.

[Jack]

You were talking about absolute zero in your original post. I was assuming you were trying to get there.

But what you're proposing here would mean finding a sweet spot somewhere. A sweet spot of piston stroke. That won't be easy.

[Tom Booth]

You were talking about absolute zero in your original post. I was assuming you were trying to get there.

But what you're proposing here would mean finding a sweet spot somewhere. A sweet spot of piston stroke. That won't be easy.

Well, no. Not trying to get to absolute zero.

What I wrote was:

Logically, to my mind anyway, a heat engine runs on heat so why should it ever be intentionally cooled? OK, Yes I know, Carnot limit and all that, the further the heat "falls" down to cold the better. So, the objective is to cool the heat engine down to absolute zero, or at least get it down as cold as possible, then heat it back up as hot as possible etc. etc.

Sounds good in theory I suppose, but is it actually true? Does it really work in practice?

The bolded part expresses what I actually think. The rest is what people keep telling me, which I have and do take into consideration and have even tried to prove experimentally, over and over for years, but so far the experiments do not come out in favor of the "Carnot Limit" or the whole principle, including the "down to absolute zero" part. For one thing a hot air engine can't very well run on hot air below 77° Kelvin since air at that temperature is a liquid. Maybe you could get closer using pure helium but still not absolute zero. Aside from that, even the most elementary experiment using a "toy" engine fails to demonstrate the Carnot limit in principle.

So no. I'm basically going with my early instincts and basic common sense. Give me heat to run a heat engine and plenty of it.

[Jack]

Fair enough, no absolute zero.

But in my thinking, because transferring every little bit of heat energy into work takes a long time if you're only bringing the fluid back to it's original size. That's why you would over expand it with a piston. But finding the efficient amount of over expansion will be tricky.

And I wonder if the engine in your video runs higher rpm because it doesn't have to lift up the displacer all the way.

After all that is sorted out in still not convinced it will actually be more powerful than a cooled engine.