Stirlingengineforum.com

https://youtu.be/UAMNDdOho8E

I came across this idea recently.

One thing that came to mind: a Stirling heat engine or "hot air" engine, using ordinary atmospheric air as the "working fluid", is really using a rather complex mixture of various gasses, all having different properties at different temperatures, different "critical temperatures" different boiling points, and may include water vapor or degrees of humidity or partial liquid.

Ordinary air, lowered in temperature, to the point of liquifaction, condenses, or having condensed, reheated slightly, expands 800x.

That is, air as a gas is 800x the volume of a drop of liquid air. And the reverse. A volume of air shrinks down 800x smaller when it condenses.

What about all the individual gases of which air is composed?

This Leidenfrost heat engine illustrates how "dry ice", normally a gas at Earth atmospheric temperatures could power an "ambient heat engine".

What gas/liquid undergoes phase change at or near ordinary atmospheric temperature and pressure?

I was wondering, if water vapor (and/or other gas/liquid) condensation or phase change in a heat engine plays a role, could a heat engine run TOO HOT resulting in a kind of Leidenfrost effect, inhibiting normal, rapid expansion/contraction.

Heat engines often seem to lag, or not run at all until they reach some certain temperature, possibly(?) where some component of the air or "working fluid" is undergoing rapid phase change induced by relatively slight temperature variations.

Perhaps it is only some relatively minor component in the air that is responsible for the majority of the expansion/contraction, or different components may come into play at different operating temperatures.

Lots of room for exploration and research.

Alcohol has a pretty low evaporation point compared to water for example. Might be suitable if you needed higher torque and lower speed.

I don't think I'd try using alcohol in any heat engine powered by an open flame or high heat, but now I'm wondering what the effect might be of putting some alcohol into a sealed "heat of your hand" type LTD engine, or an LTD running on ice.

Would the alcohol phase change between ice and ambient temperature? Would that increase power and torque?

But why lower speed? Phase change from gas to liquid, of vice versa is pretty instantaneous.

I'm suggesting "sealed", that is, maybe an LTD using a diaphragm piston to eliminate gas leaks.

Curious about what boils or liquifies at the temperature of ice, I found this chart:

https://www.engineeringtoolbox.com/boil ... d_155.html

Looks like n-butane is perfect! And, if that is the same as what's in cigarette lighters, readily available.

On ice that is.

Ether might work at "heat of hand" temperature.

Butane is apparently 1.5 times heavier than air, so keeping a regular LTD Stirling with a piston charged with it, and running on ice, might not be as much of a problem as I thought, as far as the butane escaping past the piston. It would tend to pool in the bottom of the engine anyway.

Tom Booth wrote: ↑Tue Jun 23, 2020 10:14 am I don't think I'd try using alcohol in any heat engine powered by an open flame or high heat, but now I'm wondering what the effect might be of putting some alcohol into a sealed "heat of your hand" type LTD engine, or an LTD running on ice.

Would the alcohol phase change between ice and ambient temperature? Would that increase power and torque?

But why lower speed? Phase change from gas to liquid, of vice versa is pretty instantaneous.

I'm suggesting "sealed", that is, maybe an LTD using a diaphragm piston to eliminate gas leaks.

Curious about what boils or liquifies at the temperature of ice, I found this chart:

https://www.engineeringtoolbox.com/boil ... d_155.html

Looks like n-butane is perfect! And, if that is the same as what's in cigarette lighters, readily available.

As I understand it, getting a phase change gets you more pressure, but it takes longer to change it back down to liquid without a proper condenser. I May be off about that though.
According to the chart, good old moonshine has a suitable boiling point for stirling or lamina type engines.

Phase change rocketry?

What happens when liquid air (nitrogen) warms up to ambient rapidly? In a soda bottle rocket!

https://youtu.be/m7Bo9YcmLIQ

OK, so,

In theory, butane phase changes at a much higher temperature than liquid nitrogen.

If we were to attempt the same experiment as above, could we make a similar water rocket using just butane, without having to go to -320 F?

https://youtu.be/XUDQzjZI52w

As I understand it, getting a phase change gets you more pressure, but it takes longer to change it back down to liquid without a proper condenser. I May be off about that though.
According to the chart, good old moonshine has a suitable boiling point for stirling or lamina type engines.

From what I've read about condensing gases in expansion engines, cooling by expansion in a cylinder while the gas does external "work" results in instantaneous liquefaction and the gas condenses on the cylinder walls.

"Work" generally meaning that there is some type of load on the engine. A "freewheeling" engine might not produce enough cooling. But the info comes mostly from the field of gas liquefaction at cryogenic temperatures to produce liquid nitrogen, helium etc.

Even a freewheeling LTD is doing some work resulting in external output; heat from friction, sound etc. A slight breaking of the flywheel crank should be a sufficient load at higher temperatures, but this is all experiment.

By "moonshine" you mean ethanol? Boils at 173F.

I'm not sure why that would be suitable. For an engine running on hot water it might be good.

Tom Booth wrote: ↑Wed Jun 24, 2020 11:09 am

As I understand it, getting a phase change gets you more pressure, but it takes longer to change it back down to liquid without a proper condenser. I May be off about that though.
According to the chart, good old moonshine has a suitable boiling point for stirling or lamina type engines.

From what I've read about condensing gases in expansion engines, cooling by expansion in a cylinder while the gas does external "work" results in instantaneous liquefaction and the gas condenses on the cylinder walls.

"Work" generally meaning that there is some type of load on the engine. A "freewheeling" engine might not produce enough cooling. But the info comes mostly from the field of gas liquefaction at cryogenic temperatures to produce liquid nitrogen, helium etc.

Even a freewheeling LTD is doing some work resulting in external output; heat from friction, sound etc. A slight breaking of the flywheel crank should be a sufficient load at higher temperatures, but this is all experiment.

By "moonshine" you mean ethanol? Boils at 173F.

I'm not sure why that would be suitable. For an engine running on hot water it might be good.

173F is a convenient boiling point for an engine as it's high enough that the average environmental temperature is low enough for it to condense while being an easy temperature for a heat source to reach. It's also low enough that the engine doesn't need specialized alloys. Plus it's relatively cheap and readily available and you can make it yourself if need be.

It would certainly be quite interesting to see if an off the shelf "high temperature" Stirling, charged with alcohol could run efficiently on a "low grade" heat source.

After watching those water rocket videos, I'm looking forward to the little LTD Stirlings I ordered arriving, so I can try charging one with butane, with some trepidation.

Should I wear gloves and face shield? Could it explode?

That would actually be a promising result. Just have to build a much sturdier engine out of cast iron or something that can take the pressure.

Those apparently, quite high powered water rockets are really being fueled by just the available heat in the surrounding atmosphere.

Why burn fuel in an engine if it can just be expanded in a cylinder to drive an engine on ambient heat, then condensed and used over again?

Probably butane could be kept liquid by just keeping it in the freezer. I have been frustrated trying to light a butane lighter in cold weather. It becomes necessary to warm the lighter up a bit by breathing on it or using friction, rub it on your pant leg for a minute.

Putting the butane lighter or whatever in the freezer to keep the butane liquid, would make it easier to add a drop or two to an LTD engine on ice, without the pressure and rapid evaporation before it can be gotten running.

Tom Booth wrote: ↑Wed Jun 24, 2020 1:54 pm It would certainly be quite interesting to see if an off the shelf "high temperature" Stirling, charged with alcohol could run efficiently on a "low grade" heat source.

After watching those water rocket videos, I'm looking forward to the little LTD Stirlings I ordered arriving, so I can try charging one with butane, with some trepidation.

Should I wear gloves and face shield? Could it explode?

That would actually be a promising result. Just have to build a much sturdier engine out of cast iron or something that can take the pressure.

Those apparently, quite high powered water rockets are really being fueled by just the available heat in the surrounding atmosphere.

Why burn fuel in an engine if it can just be expanded in a cylinder to drive an engine on ambient heat, then condensed and used over again?

Probably butane could be kept liquid by just keeping it in the freezer. I have been frustrated trying to light a butane lighter in cold weather. It becomes necessary to warm the lighter up a bit by breathing on it or using friction, rub it on your pant leg for a minute.

Putting the butane lighter or whatever in the freezer to keep the butane liquid, would make it easier to add a drop or two to an LTD engine on ice, without the pressure and rapid evaporation before it can be gotten running.

If there is a question of something exploding then yes, always wear protective gear. Even if a thing doesn't explode, cracking can just as easily put speck of something sharp in your eye.

A safe experiment while still waiting for my engines to arrive.

I bought some lighters today. I'm not 100% sure what they contain, presumably butane, but the package did not specify.

I wanted to see just how much phase change (expansion and contraction) I could get from butane, between an ordinary freezer and ambient (about 60F) compared with air.

So I removed the flint and striker from the lighter, just to avoid any accidental spark, and injected some butane into a balloon. Then filled another balloon with air to the same size.

At first I used quite a lot of butane but found that if the balloon was inflated too much the butane leached right through the rubber very quickly. This did not seem to happen as long as the balloon was barely inflated.

After this initial experimenting, I put some butane (or whatever lighter fluid) in one balloon, let it warm up to room temperature. (The liquid butane became very cold outside of the lighter).

After the balloon warmed up, I inflated another balloon with air to the same size.

Then I put both balloons into the freezer and waited a few minutes.

Taking them out they looked like this:
The butane filled balloon had clearly deflated, but the balloon with regular air had not changed in size noticeably. I had to be quick taking the picture, as the butane balloon was already begining to reinflate the moment I took the balloons out of the freezer

Less than a minute out of the freezer the butane filled balloon was fully reinflated.
The butane caused a greenish discoloration.

This was repeated several times, returning the balloons to the freezer and taking them out again, back in again, etc.

The results were the same each time.

The air balloon did not change noticeably in size between room temperature and freezer, but the butane balloon continued to expand and contract as shown in the photos.

Containment of butane in an engine could prove challenging, though it does not seem to leach through the plastic lighter it came in so readily as it does through a balloon.

So, perhaps it might be possible to get a little more action out of an LTD Stirling running on ice, with a little butane in the chamber. I suspect the butane might not be kind to a foam displacer, or a diaphragm piston made of rubber though.

Just FYI

The green discoloration, which puzzled me, was actually from coloring added to the lighter fluid itself by the manufacturer.

The lighters come in different colors, which I had thought was the color of the plastic, so paid no attention to, but is actually coloring added to the fluid. The plastic is clear.
For any future experiments I'm going to get some "food grade" n-butane of known purity, used by restaurants for making Crème brûlée and free of coloring and other impurities. Who knows what is actually contained in these cheap lighters.

Make sure any rubber or plastic components are rated for containing stuff like butane. Some fuels will eat away at those that aren't.

Plastic soda bottles do much better than balloons.

This is the third time I've cycled these in and out of the freezer:
After a minute out of the freezer:
Does that butane bottle look a bit swollen?

It looks like I'm absolutely getting more expansion/contraction from the butane. And so far it does not seem to be leaking.

I'm not really sure how much butane got into the bottle, I just held the lighter upside down over the mouth of the bottle for a while with the valve open. There was some visible spray of liquid, but likely there is still some air in the bottle mixed with the butane.

I think I might get better results if I could somehow evacuate all the air from the bottle first. For now I just relied on the butane to displace the air.

I had a bit of liquid butane in the bottom of the bottle then I screwed the cap on loosely and let it sit till the liquid completely evaporated, then unscrewed the cap slightly to relieve the pressure then put it on real tight.

Of course the bottle with plain air is also screwed down equally tight, as far as I was able to judge hand tightening.

The last time I put the bottles back in the freezer, I opened the freezer again very shortly thereafter and I was surprised at how quickly the butane bottle collapsed the second time around. Probably because it had not been out long and so the bottle was still somewhat chilled, though I did give it time to completely re-expand before returning it to the freezer.

I'm not too concerned that it does take some time for expansion and contraction. The dynamics are not the same as in a running engine.

I'm generally optimistic this will give a considerable boost in performance to a Stirling running on ice. I'm still waiting for my engine kits to arrive.

I'm looking at other gases that might be worth a try.

neopentane, (2,2-dimethylpropane) which is a constituent of natural gas, in very small quantities and apparently fairly non-toxic, except at high concentrations, has a boiling point about 10 degrees above freezing. Also "a highly volatile liquid on a cold day, in an ice bath, or when compressed to a higher pressure" - Wikipedia

Highly volatile sounds good to me for this application.

I thought something that condenses a few degrees above freezing might work better than at or below freezing because the air in a running engine will have some mixing so the cold side, on ice, might be several degrees above freezing on average. Neopentane has no particular use, so is not readily available, except as a "research chemical" . About $75.00 (with shipping) an ounce (or less, 25 milliliters) on Ebay. Expensive, but there doesn't seem to be any restrictions on just ordering some.

I guess its no wonder people call me a mad scientist.

Oh, I should probably mention it is a good idea to put the pop bottle (and lighter) in the freezer for a while to get it good and cold before trying to add the butane to the bottle. Otherwise the butane just tends to boil off before you can get the cap on. It took me several attempts before I got any results worth mentioning. Frustrated at the butane just disappearing I put the bottle in the freezer, then it remained a liquid in the bottle long enough to get the cap on. And don't use too much and don't screw the cap on tight until the pressure is off, and don't forget the stuff is highly flammable, yada yada yada.