fuel consistency

In message <[email hidden]>, Roger
<[email hidden]> writes

Quoted message said:

The message <[email hidden]>
from Chris Townsend <[email hidden]> contains these words:

<Chris Street>

Quoted message said:

Quoted message said:

It's wrong for the same reason that a bottle of vodka doesn't separate into
alcohol and water. Propane and butane are perfectly miscible and they mix
entirely thus the evaporative surface consists of a mixture of liquids -
therefore you get a gaseous mixture as well.

If you are foolish enough to keep your vodka in an unsealed container
why shouldn't the alcohol and water evaporate at different rates, they
have different boiling points?

Quoted message said:

What then causes the rapid fall of in performance? Just the pressure in
the cartridge falling?

I would have thought that was basic physics - latent heat of evaporation
(or whatever they call it these days). Turning the liquid into gas needs
a specific amount of energy which cools the remainder of the liquid. As
the reservoir is depleted there is less liquid to provide this heat and
the temperature of the remainder thus drops more quickly.

This is what happens with any gas cartridge. The puzzling thing with
butane/propane mixes is that while the power is phenomenal when the
cartridge is full - a gas stove with a new cartridge will bring water to
the boil faster than a petrol stove - it falls away very quickly in cold
weather. With a pure butane or pure propane cartridge there is a much
less dramatic fall off in performance.

Once a cartridge is less than 2/3 full the performance never returns to
that when it was full, regardless of the temperature and even when the
cartridge is warm and the stove has just been lit.

If you run a gas stove for a long period the cartridge cools and
performance drops, fitting in with the basic physics. This occurs at any
temperature but it much more noticeable in the cold.

In message <[email hidden]>, Boo
<Boo@spam_me_no_spam.net> writes

Quoted message said:

Quoted message said:

Quoted message said:

Pot of hot water. Dunk gas bottle in it. If you hands can tolerate the
temperature of the water then the gas cartridge won't go bang or anything
daft like that.

Oh, we did that. The water and cartridge cooled down very, very
quickly.
We also stood cartridges on top of pan lids on pas on a stove.

Why not try a vertical arrangement of several stoves so the ones below
warm the ones on top ? Braced with spare guylines it should be quite
feasible - a kind of culinary post office tower :-)

We did that too! It works with a stove that fits on top of a cartridge
on top of a pan on a hose connected cartridge. You need care though and
not to need to get at the lower pan very often. It's also quite
difficult to protect from the wind and you still have to keep the lower
cartridge warm.

The real answer is not to use cartridge stoves (except Coleman X ones)
in sub zero temperatures for group cooking. On all other such trips I've
used petrol/paraffin stoves and they've worked fine.

"Roger" <[email hidden]> wrote

Quoted message said:

Quoted message said:

Quoted message said:

It's wrong for the same reason that a bottle of vodka doesn't separate

into

Quoted message said:

Quoted message said:

Quoted message said:

alcohol and water. Propane and butane are perfectly miscible and they

mix

Quoted message said:

Quoted message said:

Quoted message said:

entirely thus the evaporative surface consists of a mixture of

liquids -

Quoted message said:

Quoted message said:

Quoted message said:

therefore you get a gaseous mixture as well.

Quoted message said:

If you are foolish enough to keep your vodka in an unsealed container
why shouldn't the alcohol and water evaporate at different rates, they
have different boiling points?

I believe water and alcohol will generally evaporate at different rates.
The vapour coming off a mixture of alcohol and water will be more alcohol
than water. There are also mixtures of liquids though (termed azeotropic I
think) where at certain concentrations they do act as one. I think in the
case of water and alcohol this is 96% alcohol and 4% water (?). This will
boil at one single temperature and the vapour from any evaporation will
still be 96% alcohol and 4% water.

So either butane propane mixtures are azeotropic over the range of
concentrations found in camping cylinders and don't vaporise independently
or maybe the propane initially vaporises more easily until the remaining
mixture reaches a concentration ratio which is azeotropic and then they
vaporise together? I've no idea which but the manufacturers ought to be
able to tell you.

I don't have much experience of stoves but if cooking at low temperatures is
a problem as it appears to be, doesn't anyone make small just propane
cylinders you can use? Why for caravans and not for backpackers?

In message <[email hidden]>, AndyP
<[email hidden]> writes

Quoted message said:

"Roger" <[email hidden]> wrote

Quoted message said:

Quoted message said:

>It's wrong for the same reason that a bottle of vodka doesn't separate

into

Quoted message said:

Quoted message said:

>alcohol and water. Propane and butane are perfectly miscible and they

mix

Quoted message said:

Quoted message said:

>entirely thus the evaporative surface consists of a mixture of

liquids -

Quoted message said:

Quoted message said:

>therefore you get a gaseous mixture as well.

Quoted message said:

If you are foolish enough to keep your vodka in an unsealed container
why shouldn't the alcohol and water evaporate at different rates, they
have different boiling points?

I believe water and alcohol will generally evaporate at different rates.
The vapour coming off a mixture of alcohol and water will be more alcohol
than water. There are also mixtures of liquids though (termed azeotropic I
think) where at certain concentrations they do act as one. I think in the
case of water and alcohol this is 96% alcohol and 4% water (?). This will
boil at one single temperature and the vapour from any evaporation will
still be 96% alcohol and 4% water.

So either butane propane mixtures are azeotropic over the range of
concentrations found in camping cylinders and don't vaporise independently
or maybe the propane initially vaporises more easily until the remaining
mixture reaches a concentration ratio which is azeotropic and then they
vaporise together? I've no idea which but the manufacturers ought to be
able to tell you.

I don't have much experience of stoves but if cooking at low temperatures is
a problem as it appears to be, doesn't anyone make small just propane
cylinders you can use? Why for caravans and not for backpackers?

Cooking at sub zero temperatures is only a problem if you use a
butane/propane cartridge stove other than a Coleman X one. Petrol,
paraffin and alcohol stoves all work fine at low temperatures.

The problem with propane is that it needs a much heavier cartridge than
butane as it's more volatile. Even small propane cartridges are heavy.

There's some interesting information on this site, which states bluntly
that the propane burns off first in butane/propane mix cartridges:

http://home.comcast.net/~agmann/stove/Canister.htm

"Chris Townsend" <[email hidden]> wrote

Quoted message said:

AndyP [email hidden]> writes

Quoted message said:

So either butane propane mixtures are azeotropic over the range of
concentrations found in camping cylinders and don't vaporise

independently

Quoted message said:

Quoted message said:

or maybe the propane initially vaporises more easily until the remaining
mixture reaches a concentration ratio which is azeotropic and then they
vaporise together? I've no idea which but the manufacturers ought to be
able to tell you.

Quoted message said:

There's some interesting information on this site, which states bluntly
that the propane burns off first in butane/propane mix cartridges:

http://home.comcast.net/~agmann/stove/Canister.htm

Yes, sounds sensible to me that it would do at low temperatures. Reading my
previous post back it sounds as though I was trying to argue that it
wouldn't which I wasn't meaning to (I think I mislaid a sentence in the
editing).