A New Type of Hot Air Engine

[VincentG]

Welcome KristofB1982.

Pardon the pathetic animation, but with designs changing this rapidly its not worth investing much time at this stage. Luckily my 3d printed prototype is easily adapted to this new design.

Matt, set your eyes upon this scheme. I think it solves the reservoir issue as well as flow restrictions, complexity and sealing issues, and a host of other concerns. The dark area on the end of the heat pipe is some sort of ceramic insulator, and the bottom of the displacer needs to be insulated as well, if not the whole thing. Though if the displacer is metalic(or at least its ID bore) it can serve as extra heat exchanger area.

The piston is shown bashing the displacer but it should easily be converted to ringbom. The secondary compression cylinder should be ceramic or thin metal of low thermal capacity. Note that the bottom most fin of the heat pipe is a larger diameter than above to allow air to flow as soon as the displacer is moved up. The displacer has no perfect seal at its ID or OD and the space occupied by the spring should be of no consequence due to tight tolerances restricting rapid flow.
https://photos.app.goo.gl/jDnnNBvZBuMfX4X4A

ringbom expansion picture.jpg (273.94 KiB) Viewed 2504 times

ringbom compression picture.jpg (297.41 KiB) Viewed 2504 times

[matt brown]

When I first saw Tom's hot potato, I immediately saw something similar...but with the hot potato fixed to a sliding hot rod thru the hot chamber head with something like a ceramic sleeve for bearing and insulation. As I said, there's so many ways to game this chase !!! Putting aside the potato & heat rod, your current design has a feature in my favorite Otto scheme: a central 'sleeve' valve. The reason I said 'perfect' seal recently is to stress that distinct processes are more important for low end schemes than high end schemes (high end have more leeway). Taken to the other extreme, a typical thermal lag doesn't even have an orifice port, but rather the whole cylinder bore is exposed (blocked only by matrix). If the working compression is not fairly isolated from the hot chamber, then heat will 'leak' to working chamber during compression, thus increasing the backwork. This will manifest itself as less Wpos (stall engine if extreme) but the hidden gem is that the efficiency of Otto is linked to the deltaT of the compression ratio (yep, a Carnot thing). The main issue is to maintain expMEP>compMEP and your observation of a high peak pressure driving scheme is xlnt !!! (just like ICE).

[matt brown]

If I was making youtube videos, I could easily convince Tom how Carnot buzz works (when it does AND doesn't apply) with one short video. Meanwhile, this Otto scheme will succumb to Carnot where a 3:1 compression ratio has .35 eff potential when diatomic (air) and .50 eff potential when monatomic (Ar). However, this is only when the expansion ratio is also 1:3, and scheming the expansion ratio greater than the compression ratio (aka Atkinson) will increase eff for both diatomic & monatomic gasses. So, a simple scheme with a well insulated cylinder and simple mechanics devoid of typical ICE claptrap accessories should be able to at least compare to common ICE eff. It's almost a nobrainer and why I think Uncle Sugar knows how to do it, but hides it to maintain the status quo. Any major change to the current setup would be far more disruptive than when the ICE put the buggy whip makers out of business...

[VincentG]

Matt it seems maybe we are on the right track then. Btw I am dying to see these high end schemes you talk about. Any links?

Had some time to hit the lathe(and some hard cider) and came up with this from some brass rod I had. It can be improved a lot with a thinner slitting saw, wire EDM, or a brass filter extrusion. This should work for now. It was easily adapted to my latest 3d printed housing. The more I think about this design the better it seems to get. It has nearly no dead space and all of the working gas can be highly compressed towards the heat rod. Best of all it's dead simple with no seals besides the piston. I'll leave the secondary compression for larger models down the road.

I can picture adapting to multi cylinder use with a "spider" like solid copper rod going to each cylinder from a common heat source. If ringbom, the displacers stroke can easily be regulated with a magnetic coil arrangement to allow throttling/idle.

sleeve valve prototype off.jpg (166.86 KiB) Viewed 2492 times

sleeve valve prototype on.jpg (151.64 KiB) Viewed 2492 times

[matt brown]

Btw I am dying to see these high end schemes you talk about. Any links?

I meant low end=low compression, high end=high compression (like ICE). Most guys think seals are more important with higher compression than low compression. Well, bad seals in high compression will lower performance, but bad seals in low compression will nix scheme (less to loose).

Be advised that brass has fairly low conductivity vs copper or aluminum (check online if unknown).

I'm slowly finalizing my pseudo alpha SE design which is similar the JD#6 in size, but without all the Rube Goldberg claptrap. I opted to go with a fairly large 'model' with ~4" bores to facilitate using a legendary ICE part, but now know this ICE part won't work as expected. Oh well, a little more machine work, and since I lack machinery, I'm hoping to have a local guy help out. This guy is a well known ECE guy with a garage full of machinery, the type of guy that could make my 'mod' engine without drawings. This design is what most DIY guys in the Stirling camp expect, so I'm OK with it, but not the Holy Grail. Sometimes ya just gotta go with the flow and go with what works first and pursue what you want later.

[VincentG]

I'm slowly finalizing my pseudo alpha SE design which is similar the JD#6 in size, but without all the Rube Goldberg claptrap

Looking forward to a post about this. I am fortunate enough to have machinery and the ability to use it. Without that this would be a nearly impossible task for me, at least with how much I change my mind on designs.

After a good dinner, I've realized that the space above the displacer, with further development and some clever porting/reed valve arrangement, can be used as the "hot air injector" I have thought about.

I've realized that although aluminum has great thermal conductivity, its high specific heat may be detrimental to these engines.

I'd also like to ask if anyone can help me calculate the amount of btu's that can be transferred through a given diameter and length of metalic rod. My hope is to neck down the hot rod where it enters the engine to only allow the max theoretical btu consumption of the engine through, to easily avoid overheating issues.

[Tom Booth]

...

Note that this is not perpetual motion of course. But maybe more akin to tesla ambient energy scheme where energy is needed to start the process. ...

You've got me curious. What is your view regarding that (Tesla's ambient heat engine)?

With your prototyping skills, why not build it? Or something based on the same principle.

[VincentG]

Tom, as stated I think this is a sort of similar machine. If we can use some of the heat input energy to in effect open up the consumptive power of a space vacuum to have a limitless sink to flow heat into. Carried out to its fullest potential it may involve two tesla turbines and some tesla valves. But I am already chasing a pie in the sky, though a breakthrough seems around the corner at this point. One thing at a time.

And this, from the link you provided me. Though all of the individual links within are sadly no longer available. And internet searches turn up no information on their schemes.

As much as I love all these inventors, they are the starry-eyed ones who got suckered on their own fantasies about this possibly real technology which is--let's face it--not wanted on a planet that's being run for a profit. (See the Laws of Thermodynamics, which state that your profit is someone else's loss.) The starry-eyed whose projects were ended by mistakes, misfortune, and as often as not, financiers taking control of everything and selling it off to the highest bidder. Whose identity we will not mention here. But if anyone did manage to sail free of the gas engine and the energy monopolies, well, they still gave up marketing it, or sold it outright, or just kept it to themselves for their own use. I can't imagine why.

[Tom Booth]

Tom, as stated I think this is a sort of similar machine. If we can use some of the heat input energy to in effect open up the consumptive power of a space vacuum to have a limitless sink to flow heat into. Carried out to its fullest potential it may involve two tesla turbines and some tesla valves. But I am already chasing a pie in the sky, though a breakthrough seems around the corner at this point. One thing at a time.

And this, from the link you provided me. Though all of the individual links within are sadly no longer available. And internet searches turn up no information on their schemes.

As much as I love all these inventors, they are the starry-eyed ones who got suckered on their own fantasies about this possibly real technology which is--let's face it--not wanted on a planet that's being run for a profit. (See the Laws of Thermodynamics, which state that your profit is someone else's loss.) The starry-eyed whose projects were ended by mistakes, misfortune, and as often as not, financiers taking control of everything and selling it off to the highest bidder. Whose identity we will not mention here. But if anyone did manage to sail free of the gas engine and the energy monopolies, well, they still gave up marketing it, or sold it outright, or just kept it to themselves for their own use. I can't imagine why.

Yes, unfortunately the site owner, whom I correspond with, went through something of a personal crisis with the whole epidemic and took down the site, as well as the associated forum. All but the list of names, but he says he is, or will be gradually rebuilding the site. He also sent me a zip file of the content a while back. Some pages are also preserved on the Way back archive.

At any rate, the basic concept is simple.

Anyone who has operated an air compressor is aware of the "problem". There used to be a banner on that site saying "compressed air is solar energy" or some such logo. More precisely I'd say, the heat generated by compressing air is mostly solar energy.

There is something of a myth that the heat from a compressor is from the "work" of the electric motor running the compressor, but that is only partly true, if true at all.

Having studied a good many of those inventions, the ones that seemed credible were essentially just air compressors that in one way or another made use of the ∆T and or ∆P or both.

I mentioned earlier the tremendous heat generated by the YONG HENG. Then there was also this video demonstrating what our friend Matt claims "never happens".

https://youtu.be/2hYQtB4QkEY

I'm pretty sure even your little LTD could operate some kind of miniature bicycle pump to generate a little extra heat.

Maybe something like:

Self_Cooling_Stirling_5.jpg (104.36 KiB) Viewed 2453 times

If heat doesn't actually go through a heat engine, maybe a thermal lag version might look something like:

ezgif.com-optimize.gif (552.07 KiB) Viewed 2453 times

Basically the "hot potato" engine in an ice box. All but the hot end.

[VincentG]

I like the second illustration a whole lot. Once you get past 3 or so moving parts I think its time to step back and redesign. The right solutions are always the simple ones.

The compressor freezing air is so dependent on the humidity of the air in the tank and the air outside the tank. As well as the shape of the valve and pipes leading out.

Nevertheless, the point being, that the world around us has limitless energy. We just need a way to tap into it. At the highest level, this is Tesla's wireless energy scheme.

[Tom Booth]

Here's a sketch from way back, I don't know when. The compressor hot air pipes were supposed to be engraved right into the top plate of the engine.

The two cylinders on the right being a double acting compressor

LTDcompressor.gif (7.36 KiB) Viewed 2448 times

I've had these things posted on various forums for many years.Eventually I may get around to putting something together, but the way you work, you could probably have it done in a day or two.

[Tom Booth]

I like the second illustration a whole lot. Once you get past 3 or so moving parts I think its time to step back and redesign. The right solutions are always the simple ones.

The compressor freezing air is so dependent on the humidity of the air in the tank and the air outside the tank. As well as the shape of the valve and pipes leading out.

Nevertheless, the point being, that the world around us has limitless energy. We just need a way to tap into it. At the highest level, this is Tesla's wireless energy scheme.

Don't know about that.

Wireless is, IMO just a means of delivery. You still need a generator/source of energy, which seems to have been his solar/ambient air heat engine.

Expanded compressed air does not depend on humidity in any way. Humidity just limits how cold you can go due to water vapor freezing and clogging up the works. The real cold is generated by expansion through an engine or turbine taking out "work".to produce cold.

[VincentG]

Tesla's wireless transmission took advantage of the natural resonance of the earth. In my eyes that is using ambient energy to his advantage.

Water vapor has a major impact on the specific heat of air, so I think its relevant to the cooling effect of compressed air expanding and the efficiency of our hot air engines all the same. The compressed air expanding is the same as the expansion cycle towards BDC I'd say. We want all of the temperature loss taken from the air to create as much vacuum as possible, not to get stuck in frozen water.

The relationship of air's PVT is why these engines have so much to offer. Water is detrimental to this in a huge way.

As always, I'm not preaching (who am I to do so), just thinking out loud.

[Tom Booth]

Tesla, and others, were thinking utility scale, liquid air, cryogenic cold. That inevitably gets complicated.

For a little LTD model proof of concept I don't think it's really a worry. Keep it above 0°C.

Dry air alone will take it down much further. I've been thinking lately though that going up with higher temperatures is better than going down.

Anyway, a practical Stirling engine running on a wood fire would be a huge step forward.

[VincentG]

Agreed, it's easy to get bogged down in the minutia of all this. Thats what I was trying to avoid in the first place. I'm just trying to offer a fresh look from first principals thinking.

I truly believe that with a well-designed and machined engine, we will have both temperature extremes available to us.