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Posted: **Sun Jun 28, 2020 7:48 am**

Tom Booth wrote: ↑Sat Jun 27, 2020 5:18 pmHighly volatile sounds good to me for this application.

Why? Something being explosive doesn't have a lot to do with it's rate of expansion unless you intend for it to explode.

Posted: **Sun Jun 28, 2020 11:49 am**

"Volatile" when referring to a substance, in this context simply means that it transitions from a liquid to a gas, (boils or evaporates, changes state) readily.

An explosive expansion is what is wanted in an engine to drive the pistons, generally.

The problem is that such explosive expansion, as is standard and commonplace in an IC engine has been difficult, to near impossible to achieve in an external combustion heat engine.

Engines RUN on controlled explosions.

One problem I'm noticing, which I'm not sure if it will be a problem in a running engine is; fresh out of the freezer, if I set the pop bottle with the condensed liquid butane down where air flow around it is blocked, it tends to just sit there in a cold crumpled up state, without taking in much heat for expansion. If I pick it up, so there is more air circulation around the bottle, it then will expand rapidly.

Fresh from the freezer, some liquid butane can be seen to have accumulated.

: IMG_20200628_141817075_crop_73_resize_36.jpg (26.14 KiB) Viewed 4103 times

Sorry, the picture is blurry, but I don't have much time to focus. A few seconds later that bit of liquid butane evaporated, re-expanding the crumpled bottle.

Posted: **Mon Jun 29, 2020 1:29 pm**

Tom Booth wrote: ↑Sun Jun 28, 2020 11:49 am "Volatile" when referring to a substance, in this context simply means that it transitions from a liquid to a gas, (boils or evaporates, changes state) readily.

An explosive expansion is what is wanted in an engine to drive the pistons, generally.

The problem is that such explosive expansion, as is standard and commonplace in an IC engine has been difficult, to near impossible to achieve in an external combustion heat engine.

Engines RUN on controlled explosions.

One problem I'm noticing, which I'm not sure if it will be a problem in a running engine is; fresh out of the freezer, if I set the pop bottle with the condensed liquid butane down where air flow around it is blocked, it tends to just sit there in a cold crumpled up state, without taking in much heat for expansion. If I pick it up, so there is more air circulation around the bottle, it then will expand rapidly.

Fresh from the freezer, some liquid butane can be seen to have accumulated.

IMG_20200628_141817075_crop_73_resize_36.jpg

Sorry, the picture is blurry, but I don't have much time to focus. A few seconds later that bit of liquid butane evaporated, re-expanding the crumpled bottle.

Ah, gotcha. Plastic doesn't conduct heat as well as metal, and the movement of the piston will stir things up so it probably won't be an issue in an actual engine.

Posted: **Mon Mar 01, 2021 10:18 am**

I can report that my attempts to power an LTD on ice, charged with butane, using ambient heat, have been a complete failure.

My general impression is that a lot of heat is required for phase change, which is why a butane rocket needs a lot of water, which can hold a lot of latent heat.

Without some means of delivering a lot of heat all at once to the liquid butane, it is rather like trying to boil a pot of water with heat of the hand. There is no rapid phase change.

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