A New Type of Hot Air Engine

[Tom Booth]

...

It has me thinking too.

https://en.wikipedia.org/wiki/Vacuum_en ... nktion.gif

...

The Wikipedia references actually appear to confirm my observations. An adiabatic expansion continues after the intake valve closes.

Personally I would say this almost non-existent adiabatic expansion phase is critical to the engines operation, and as VincentG suggested at the start of the thread, again:

The overextension towards BDC and TDC due to momentum is what must help change the temperature of the gas much quicker than any heat exchanger could ever hope to.

The cooling from any air fins or water cooling being negligible, or actually detrimental, constituting a parasitic loss of heat/energy needlessly going to waste.

The potential heat of compression that could possibly be generated on the return stroke is also blown off, back out the relief valve and/or intake port.

I might redesign the engine to at least partially resolve these problems, first by, as usual, eliminate the active cooling of whatever sort and make the engine body non-heat conductive to retain as much heat in the hot intake gas as possible. Limit the intake, closing the valve sooner so as to increase the proportion of adiabatic cooling via expansion work.

How to retain any heat of compression during the return stroke is a bit of a stickler but not insurmountable.

The spent gas needs to be exhausted and fresh intake air needs to be heated

I think my suggestion of an internal and external regenerator acting as heat exchanger might help.

The exhaust could be delayed until actual TDC (full compression) or even later, so as to take advantage of the "adiabatic bounce". Then as the piston is accelerating away from the intake port, the port can open with a slight backwards reactive "exhaust" through the regenerator, just before a brief intake that will reclaim the exhaust heat.

The closed valve at TDC will provide a launch pad for adiabatic compression/bounce, any heat of compression being retained in the internal regenerator,

After the piston "launches" after TDC like a rocket, the valve opens and the exhaust heat is also reclaimed and transfered back with the intake, something similar to a pulse engine.

This would be a very rapid exchange, possibly consisting mainly of reheated exhaust gases with some portion of fresh oxygen.

I was thinking that perhaps two ports might work better, side by side in some way so the exhaust and intake air do not mix, but probably a pulse jet -like rapid exhaust/intake would suffice.

An exhaust jet shooting outward almost simultaneously with the intake gas streaming back in from the sides.

If the timing could be gotten just right, a regenerator might be superfluous.

So much for my imaginary ideal flame licker cycle.

I would think, at least some form of external regenerator or heat accumulator could retain much of the heat from the burning candle between the very brief intake moments.

My general heat engine design philosophy has become, there is never any advantage in throwing away any heat. Cooling should be by expansion work only.

[Tom Booth]

Come to think of it, the improved (in theory) "flame licker" cycle just described is essentially a fire piston with a regenerator and valve at the bottom to retain the heat of compression and also admit additional fresh warm air.

The early claims regarding this engine were that it was "atmospheric" and ran at "almost no cost"

What I've described is mostly just a relatively minor valve timing adjustment. I think it might be well worth examining the patent(s) to see what the inventor intended in regard to the valve timing and such. Maybe, I'm only bringing the timing back to what the inventor originally intended. Might be worth a look, if the patent is available.

[VincentG]

I think it needs to pointed out, at the risk of another endless debate, that we should first define what exactly the flame licker is ingesting. It is not hot atmosphere but something completely different. The properties of the "flame" probably could justify its own thread.

Now if we use fire to superheat an intake pipe and ingest hot "atmosphere", we may have half of the carnot engine cycle and perhaps more power output.


Separately, my recent dive into the workings of rocket engines makes me wonder about a theory Tom has that the hot air is doing work against the piston by impacting it(I hope I have that right). It seems to me this is true AS LONG AS the gas is contained on the back side(the cylinder) such that the force is directed towards the piston as it moves away. This simply manifests itself at the pvt plot of air in a vessel.

The question becomes, can the hot expanding air provide meaningful force upon itself similar to the way a rocket engine propels the rocket through open space. My feeling is no but it may deserve some experiments.

My thoughts turn to pumping cold atmosphere into the right direction of a superheated all metal tesla valve. The air will be heated and expanded, but forced to move out of the valve through what looks to me as a constant volume compression cycle(reference youtube videos of the tesla valve flow characteristics). The air can then be used to power a turbine. And the vacuum generated once its going may eliminate the need for the cold air pump at the start......hmmmm....

[Tom Booth]

The overextension towards BDC and TDC due to momentum is what must help change the temperature of the gas much quicker than any heat exchanger could ever hope to.

I think I mentioned this somewhere before, on the earlier thread probably, while effectively the same, I don't consider it "over" extension. As long as the piston is traveling out (or in) the gas is expanding and "hitting a moving target" until the tipping point.

With expansion the tipping point is the gas becoming so cold the piston travel is reversed. With compression it is the opposite. The gas gets so hot the piston effectively "hits a wall" and bounces off, due to the extreme heat and pressure.

I don't think that the compression is just useless because the positive expansion work is zeroed out by compression work

It is atmospheric pressure that accelerates the piston inward. The momentum is converted to heat and pressure at TDC and added to the heat input and I think as discussed previously, the combination is greater than the sum, due to that last 1/8 inch effect.

Anyway it should be relatively easy to test. Aside from the material heat conductivity considerations, which might be tested just using insulation, there is just a redesign and timing adjustment of the cam. Maybe the inclusion of a regenerator. All fairly easily doable and testable anyway.

[Tom Booth]

I think it needs to pointed out, at the risk of another endless debate, that we should first define what exactly the flame licker is ingesting. It is not hot atmosphere but something completely different. The properties of the "flame" probably could justify its own thread.

...

From the Wikipedia references (and some others), it seems that in theory, combustion is supposed to continue inside the cylinder after the intake valve closes. That would make the flame licker a partial internal combustion engine.

It sucks in, effectively, a combustible gas, smoke and or alcohol fumes only partially ignited along with air/oxygen, so this fuel/air mixture continues to burn and generate heat inside the cylinder after the valve closes.

[VincentG]

I absolutely think what I called "over extension" is useful. Its just a term that I think helps one to visualize going past the tipping point you mention.

[Tom Booth]

...
Now if we use fire to superheat an intake pipe and ingest hot "atmosphere", we may have half of the carnot engine cycle and perhaps more power output.

Separately, my recent dive into the workings of rocket engines makes me wonder about a theory Tom has that the hot air is doing work against the piston by impacting it(I hope I have that right). It seems to me this is true AS LONG AS the gas is contained on the back side(the cylinder) such that the force is directed towards the piston as it moves away. This simply manifests itself at the pvt plot of air in a vessel.

The question becomes, can the hot expanding air provide meaningful force upon itself similar to the way a rocket engine propels the rocket through open space. My feeling is no but it may deserve some experiments.

...

It's difficult to imagine, but if kinetic theory is true, why not?

Suppose you have a ball marble or whatever rolling away and you shoot bb's at it. Those very fast moving BB's are going to transfer kinetic energy to the marble helping propel it along in spite of the absence of any apparent "pressure".

The implication of there being a mixture of hot and cold air molecules in the cylinder seems to suggest this possibility. The hottest molecules can continue to impact the piston as it nears BDC even though the gas, on average is expanding and cooling. That is how I imagine expansion work continuing all the way to BDC though the heat and pressure is rapidly declining.

At some tipping point, the few very hot molecules remaining give up their energy to the piston and there is a rather sudden reversal.

[Tom Booth]

I absolutely think what I called "over extension" is useful. Its just a term that I think helps one to visualize going past the tipping point you mention.

It may be the momentum of the piston actually does some "pulling apart" of the air molecules that are attracted to each other on some level, like stretching a rubber band. The gas is said to be "elastic".

That's a big maybe. I don't really know. I think molecular forces of attraction and repulsion may play a bigger role than generally recognized. Ideal gas law does not account for any such forces at all.

[Tom Booth]

Just another thought;

Heat in a gas causing "pressure" or expansion is generally considered something occuring in an enclosed container, though in reality(?) or according to kinetic theory, the pressure itself is only air molecules colliding with the piston and cylinder surfaces.

Energy can only be transfered as heat or to a "moving target" that has some give to it.

If the cylinder is already hot, heat cannot transfer to the cylinder walls so that leaves the piston as a recipient of the energy due to it's willingness to give way and move, converting the "heat" in the gas to mechanical motion.

So, since the energy transfer is localized at the site of impact or collision between the individual gas molecules and the piston, the cylinder being enclosed or completely sealed with a valve may not be as critical as generally believed (and that assumption includes me up until very recently).

Maybe what is most important is just having the air hotter inside the cylinder on one side of the piston. That means more molecular collisions on the inside surface of the piston

At BDC the situation is reversed. Atmosphere is of course completely open air, but we do not dismiss the idea that it is nevertheless exerting pressure, though not apparent

This is somewhat speculative, but, I think logical or reasonable.

I kind of observed something like this recently experimenting with the glass over the acrylic/magnetic engine

After running for an hour or more, heat was building up under the dome (glass cylinder covered by insulation).

When I lifted the insulation, letting out the warm air, the engine stopped.

This happened several times, so I don't think it was a coincidence

It seemed as though the warm air trapped above the engine was somehow contributing energy to it's operation. This warmer than ambient "atmosphere" when suddenly removed, effectively removed part of the engines effective heat input: the hot air trapped above the piston.

My interpretation may be off, but that's my working hypothesis at the moment.

[VincentG]

While I think there is a force being exerted, it seems, to use your bb analogy, the weight of the gas molecules is insignificant relative to the weight of the rotating assembly. Although I guess that at extreme temperatures, the speed of the molecules may increase this force enough to be useful. Thankfully, we don't really need to understand all of this to have a functioning engine. We can substitute by observing a "phenomenon" and simply trying to reproduce it/use it to our advantage.

As Neil deGrasse Tyson has said, if you keep asking why, you either end up a quantum physicist, or insane.

[VincentG]

Tom I missed your latest post before I sent mine. Absolutely, as long as the rate of expansion exceeds the flow capacity of the port and atmospheric pressure, there will be a pressure wave, that can be used to our advantage. This is where I feel the tesla valve comes into play, as it manages to restrict backflow and encourage forward flow all at the same time.

[Tom Booth]

Tom I missed your latest post before I sent mine. Absolutely, as long as the rate of expansion exceeds the flow capacity of the port and atmospheric pressure, there will be a pressure wave, that can be used to our advantage. This is where I feel the tesla valve comes into play, as it manages to restrict backflow and encourage forward flow all at the same time.

Not sure how or where or in what way you intend using a Tesla valve, but have you run across my toroidal "improved" Tesla valve here on the forum?

I thought it was an original idea on my part, then years after I came across Tesla's "death ray" apparatus, I think it was, if I remember right, which appeared to have such a toroidal one way valve.

Resize_20230323_153456_6120.jpg (216.87 KiB) Viewed 3422 times

The apparatus very much resembles a live steam ejector. (Or injector).

[VincentG]

I have not, I will take a look at it.

[Tom Booth]

I have not, I will take a look at it.

I think I first mentioned it on page 2 of this thread:

viewtopic.php?f=1&t=2699

Earlier on other forums somewhere. but the OP on that thread did some computer modeling and apparently the thing does do something interesting.

Starts getting interesting here:

viewtopic.php?f=1&t=2699&start=15#p13153

[VincentG]

Fascinating read.
Do we know what happened with normandajc's proposed engine?