Bob O'Neil Air Engine

[Tom Booth]

OK.

Well, I've come up with some rough figures about what might be possible in regard to cooling due to forced expansion alone. This does not factor in possible additional cooling by Joule Thompson throttling through a valve or possible additional cooling due to the water jacket reducing the temperature of the cylinder - just expansion.

I wasn't really able to get anywhere with pv=nrt, though it is applicable, the calculations involved are way beyond me, but I found some information relating to the expansion of air due to pressure drop from elevation. This is, it seems to me real world data relating to Air, which is not an "Ideal Gas" exactly anyway.

Using various online sources / calculators / charts etc. I've come to the conclusion that for Air, there would be an approximate 10 degree F drop in temperature for every loss of 1 psi due to expansion (or pressure reduction).

Starting at roughly 14.5 psi at sea level, I'm assuming that expanding that to twice the volume would result in cutting the pressure in half to about 7 psi.

So expanding air to twice its volume would result in a drop in temperature of about 7 X 10 or 70 degrees F.

In other words, if the cylinder can hold 1 pint of air, but due to the strong spring holding the valve closed only about half that amount can get through, the 1/2 pint that gets through would expand to twice its volume to fill the cylinder. That is with what I'll call a medium strong spring.

So starting at 60 degrees Fahrenheit ambient air at 1 atm expanded 2 times the resulting temperature would be about -10 Fahrenheit. 10 below zero.

I'm not arriving at any of this from pv=nrt directly, though some of the sources used it. Rather this is based on pressure changes due to elevation in the atmosphere.

As you climb a mountain the pressure drops. About .5 psi per 1000 ft of elevation. (or 1psi per 2000 ft) and according to the sources, a corresponding temperature drop of about 5 F per 1000 ft.

Primary source: http://hwstock.org/adiabat.htm

also: http://www.unitarium.com/pressure and others.

Am I correct in assuming that doubling the volume of a fixed amount of air would halve the pressure ? Seems to follow from basic logic...

I'm also assuming that pressure and temperature drop due to elevation would correspond to temperature and pressure drop due to mechanical expansion, which may be wrong but I have little else to go by at this point. Again, seems logical to me.

Anyway, if anyone can come up with a refutation, correction or improvement in regard to these basic conclusions or rough estimates have at it. I'm fairly satisfied that this is relatively accurate, but I'm going about it in a very round about and indirect way.

Basically It looks like to me at this point that there could be a temperature drop from maybe 20 degrees Fahrenheit using a relatively weak spring to possibly as much as 120 degrees for a very strong spring.

In other words, it might not be unreasonable to expect cooling down to as much as - 50 F in the cylinder if a very strong spring were used which severely restricted air intake as the piston "pulled a vacuum".

In such a case the water jacket would only reduce HEATING by the surrounding ambient. That is, the water jacket might be dispensed with as it could be no colder than 32 F (the water would freeze lower than that) which is HOT compared to -50 F. But using the water jacket would improve efficiency but might not have been necessary in a small model engine such as was supposed to have been taken to the patent office.

"Throttling" or Joule Thompson effect cooling might contribute to some additional temperature reduction. With some gasses this effect (throttling) actually increases the temperature, but atmospheric Air Happens to be a mix of gases which can be cooled by throttling or Joule Thompson effect. This is not due to expansion exactly but as far as I've been able to figure, ACCELERATION as the gas rushes through the valve opening. The heat is converted into Kinetic Energy. The air molecules apparently themselves absorbing the heat to pick up energy for acceleration. A rather strange notion but that's more or less how the sources on the topic read or explain it.

If this whole compression by cooling theory is in the ballpark, than I think that also explains why the Power Pistons driving the engine don't have any water jacket for cooling in the patent illustrations.

The "compressor" cylinders do the cooling. Though not really compressors, just combination coolers and pumps working at atmospheric pressure. The actual compressor is the "equalizer" which becomes a kind of hydraulic thermal pump or compressor inside the tank.

The compression or pressurization to 200 psi to drive the power pistons takes place after the supercooled air passes the equalizer and gets into the tank due to the re-absorption of ambient heat. This re-absorption of heat continues on into the power pistons. The hotter the power pistons the more heat the gas can absorb. The more heat it absorbs, the more it expands to drive the engine, Heat due to friction would increase the power of the engine - So having a water cooling jacket around the power pistons would defeat the purpose. They are allowed to remain hot, so... no water jacket. Instead there are electric heaters!

At first I thought this whole idea was only a wild and very remote and unlikely possibility and probably wrong, but the more I look at this and think about it, I'm starting to actually take it seriously. The pieces of the puzzle seem to be falling into place.

[Motorcoach1]

Heres some PDF files to look over. The 1986 & Young file is interesting. These are all on vaccume pump technoligys. I guess your starting to see what i stumbled across when doing some test on this type engine. Still in the works

[Tom Booth]

Heres some PDF files to look over. The 1986 & Young file is interesting. These are all on vaccume pump technoligys. I guess your starting to see what i stumbled across when doing some test on this type engine. Still in the works

Thanks, it will take me a while to peruse.

Anyway, I've been thinking about a few things that I think might be important as far as design considerations, though this is mostly just my own imaginings or visualizations based on nothing.

I've been trying to figure out, regarding the large valve in the top cylinder section, how the possible cold produced by "pulling a vacuum" could be maintained.

Normally, I would think that it wouldn't. The reason being that: OK, so the piston pulls a vacuum and expands some air and the air gets cold temporarily. But when the piston goes back up to push the air out through the check valve to the line leading to the tank won't the air be re-compressed and therefore heat back up again ? It doesn't seem like there is anything to be gained by this throttling valve. If that is, in fact what it is supposed to be.

So mulling this over and imagining and visualizing this scenario.... The air is pulled in, expanded, cooled, then compressed again... Hmmm...

Then I think I hit upon the answer and discovered Maxwell's Daemon lurking in this process.

The engine was probably Cast Iron given the era. Cast Iron is a metal that can absorb and hold a tremendous amount of heat, relative to air anyway. You have a cold cast iron engine cooled with water.

Now draw a vacuum in the cylinder admitting some air. The air is not uniform in temperature on a molecular level. Air is a mix of gases. There are some high energy speedy (hot) molecules zipping around and some slow low energy (cold) molecules all pack together and bumping into one another and exchanging heat all the time. Temperature of the air is the AVERAGE kinetic energy. So there are hot and cold molecules mixed together.

When the air is drawn into the cylinder and expanded, also accelerated, While expanded in the cylinder there is more SPACE between the molecules. The space allows more freedom of movement. The molecules don't bump into each other so much or so often and move around in the cylinder more independently without colliding and exchanging heat.

So the slow cold molecules kind of meander around without bumping into anything while the HOT molecules zip around and ricochet off the cylinder walls. In colliding with the cold water chilled cast iron the high energy hot molecules transfer heat/energy to the metal and join the cold molecules. Very quickly, the heat is gone, it melts away into the metal of the cylinder to eventually be carried off through the water jacket. The AVERAGE Kinetic Energy of the gas has been reduced considerably and permanently. When it is pushed back up and out of the cylinder it doesn't get hot again. It stays cold.

There is another advantage to this.

With the arrangement Neal has for this "compressor" with the piston doing double duty...

I said earlier that it takes work or puts a load on the engine to pull a vacuum.

But there is a flip-side in that after the gas has been expanded and cooled, the vacuum will PULL THE PISTON!

If anything, since the gas has cooled by expansion and heat loss to the cylinder walls, as well as throttling, the vacuum will INCREASE, or at least it won't decrease. It should pull the piston back with just about as much force as the piston exerted to create the vacuum in the first place.

With many such compressor pistons, while one is pulling a vacuum another will be getting pulled by a vacuum, possibly with even a slightly greater force! due to the gas having cooled it will contract more potentially creating a stronger vacuum.

In other words, this compressor should be practically FREEWHEELING. No wonder that only two power pistons are needed to drive what, 14 double acting compressor pistons! That's 28 compression strokes for each rotation of the crankshaft. Seems like this would be impossible. How could just two power pistons drive so many compressors? Why not!?!?!? The compressor is practically freewheeling. Practically every bit of work it does "pulling a vacuum" and cooling the air it gets right back on each return stroke as the vacuum pulls the piston back up.

I'm really beginning to see how this engine might actually work. How it could compress more air than it uses. I'm really amazed. It seems to me this Bob Neal must have been some kind of practical Genius to have figured this stuff out and to have actually made it work.

[AlanA]

Hi Tom,
this discussion gets more and more intersting. I have to reread this tomorrow. Here it is 23:00.
My question is: Where gets this engine his power? As I have understood you mean that it gets it not from compression but from pulling a vacuum which cools the air which pulls the energy from the air (by expanding this cooled air)
What makes me thinking: It also takes power to get a vacuum. The old greeks said: Nature hates vacuum.

[Tom Booth]

Hi Tom,
this discussion gets more and more intersting. I have to reread this tomorrow. Here it is 23:00.
My question is: Where gets this engine his power? As I have understood you mean that it gets it not from compression but from pulling a vacuum which cools the air which pulls the energy from the air (by expanding this cooled air)
What makes me thinking: It also takes power to get a vacuum. The old greeks said: Nature hates vacuum.

The basis of the theory I'm working on, due primarily to the topic starter drawing attention to something unusual about the valves... I'm not really sure that what he was talking about was what I found, but anyway...

This is just my theory. I am becoming more and more convinced its right but that remains to be seen. But anyway:

Air can be reduced in volume in two ways. Either forcefully compressing the air or by cooling the air. Both will accomplish more or less the same thing.

Pulling a vacuum to expand the air temporarily is not the source of energy to run the engine. That is just one of the apparent methods of cooling used.

By cooling the air it contracts on its own without needing to be forcefully compressed.

What looks like an advantage of using this method is that much, if not all of the energy used to cool the air is gotten back immediately because after the piston creates the vacuum and the air is cooled the vacuum gets stronger due to the cooling. Having gotten colder the air contracts and pulls the piston back. That just recoups some of the power, kind of like regenerative breaking I'd say, but that isn't really what is driving the compressor.

After the air is cooled to a very low temperature, it is sent to a special valve. The valve is like a hydraulic jack, the way it looks to me. A hydraulic Jack works the same way. A hydraulic Jack is also basically just two check valves.

In a jack, between the two check valves you have a plunger that goes up and down to draw the fluid in one check valve and then force it out the other. With the valve in the Neal Engine's Tank, I think that the air itself acts as the "plunger" to pump itself through the check valves by thermal expansion from ambient heat. The cold air goes past the first check valve. Between the valves it heats up and expands forcing itself through the second valve.

The real power to drive the engine is derived from ambient heat.

Once the cold air is in the tank, the tank is surrounded by ambient heat which causes the air to re-expand to the volume it had before it was cooled. So now once in the tank and re-heated the air builds up pressure. It is the pressure created by heating the air back up with ambient heat that drives the engine.

It should be kept in mind that the engine driving the compressor is different from the compressor itself, though the two are combined in one unit on the same crankshaft. There are two power pistons driving 14 cooling units or "compressor" pistons.

The engine is driven by air pressure.

The engine then drives the "compressor"  - really a set of coolers as it looks to me. The "compressor" does the work of cooling the air so it can be easily sent into the tank.

The real source of energy powering it all though is solar energy stored in the atmosphere as ambient heat which heats the air back up and creates the pressure to run the engine.

It looks like a beautiful arrangement, but as I say, there is nothing explicitly stated in the patent to confirm this. As of yet it is just a theory. It's just one possible explanation of how the engine might have worked. I'm becoming rather convinced it might be right though.

Part of the cooling is accomplished by cold water circulating in the water jacket.

I'm not sure how necessary the water cooling is. The patent doesn't say much of anything or even show if the water is cooled by a radiator or what.

If there is an unlimited source of cold water, like a well or a stream or spring then the engine might not have been able to run without this source of "Free" cooling.

However, he is supposed to have gotten a patent by demonstrating a smaller version of the engine, wetting it on the patent examiners desk and running it. I doubt there was a well or stream or source of cold water such as that at the patent office, who knows ?

I'm not sure the small model needed water cooling.