From: Johnlebl@aol.com
Date: Sat Nov 02 2002 - 14:21:25 CST
In a message dated 11/02/2002 6:16:54 AM Central Standard Time,
KKoloff@aol.com writes:
> My experience is with a cannister the fuel operating pressure is less
> and drops as altitude increases, with a liquid fuel, you can control that.
>
> Kevin Koloff
> Oklahoma
Stove fuel is a very complex issue and understanding it is not short and
sweet so hang in there.
For this post "white gas" really means naphtha which is sold at Philmont as
stove fuel. Coleman sells the same fuel with anti aging addatives in gallon
cans.
Cannister fuel is a 60% butane 40% propane mix sold at Peak One Max fuel
cannisters. There are other brands that contain similar mixes in different
styled containers.
By the way, I brought some Philmont "white gas" home this past summer and ran
it through our laboratory for analysis. It isn a very good fuel and very
clean burning and free of imprities and water as issued by Philmont. They
are to be commended on it's quality. I'll not bore you with the hydrocarbon
makeup via gas chromotography analysis.
Kevin brings out a very good point. This observation appears to be a factor
of altitude, but in reality it is a factor of temperature.
Canister fuel is a mix of approximately 60% butane and 40% propane. Some non
pressuring pentanes are usually added to increase the heat value and for
economy.
At colder temperatures butane won't vaporize sufficient to create enough
pressure to push the gas out of the cartridge to burn in the stove. The
critical temperature for pure butane is about 50 deg F. Below that pure
butane becomes useless as a stove fuel. That is why butane tanks used for
home heating and cooking were buried underground to protect from cooler
temperatures. We rarely see pure butane used for heating and cooking any
more. Propane is much more convenient.
The reason for blending butane with propane in camping stove canisters is two
fold. Butane has a higher BTU rating per weight of fuel than propane meaning
one ounce of butane heats more than one ounce of propane. Pure propane
having a higher vapor pressure would require a stronger container, thus
heavier, than pure butane or a mix of the two. The 60/40 blend strives to
strike the sweet spot in between.
Back to the original altitude problem.
When you use canister fuel you burn off the gas, not the liquid. When you
burn off the gas you cause the vapor pressure INSIDE the canister to become
lower. When this vapor pressure becomes lower it causes the liquid fuel to
boil and give off vapor just like a pot of water boiling on a stove. This
vapor is what then burns.
The laws of physics and chemistry demand that when this liquid boils it
produces a cooling effect and thus cools the liquid inside the canister.
That is why one sees frost on a gas cylinder when fuel is extracted at a high
rate. This is the same principle that air conditioners work on.
When this liquid inside the canister cools it boils at a lesser rate and
creates less pressure which Kevin mentions above. It appears that this is
caused by altitude when in fact it is caused by temperature. Temperature and
altitude do have something in common. Usually the higher you go the cooler
it is but this is not a carved in stone fact. Other factors such as sunlight
and time of day are involved in what the air temperature and thus the
temperature surrounding the canister is.
That temperature is the only thing that will effect the rate at which fuel
comes out of a canister. The surrounding air pressure has a slight effect on
it. Altitude does play a slight part, but in the opposite way. At higher
altitude there is less pressure outside the canister and reason says the fuel
will come out faster, but the cooling effect of temperature which causes a
lowering of the temperature inside the canister offsets this probably
tenfold.
True, there is less oxygen at higher altitude to support combustion, but even
at 12,000 feet there is plenty of oxygen for stove use. It does not even
require a change in jet size to accommodate the need for more air and less
gas for complete combustion. It is just no the controlling factor.
Altitude at Philmont has a profound effect on the human body.
Altitude at Philmont has almost no effect on which fuel system or stove you
choose to use. Experience of thousands of crews has found that canister fuel
such as Peak One Max which is sold there works fine in all camps regardless
of altitude. The altitude at Philmont is just not sufficient to have a
profound effect on stove choice and fuel choice.
Kevin is correct in that with liquid fuel stoves that have a pump you can
control the pressure inside the fuel tank regardless of temperature. One can
also control the pressure inside a canister by adding or removing heat that
touches the outside of the canister. This is not always easy to do.
I don't mean things like holding a match under the canister. One way is to
warm it up against ones skin. Not very efficient when one wants to heat food
to warm the body and you are removing heat from the body to cook the food
faster. Sort of a viscous circle.
Another way is to place the canister in a warm pan of water. Warm is a
relative term. Warm as in warmer than the canister which may be pretty cold
to one's way of thinking.
With that all said, the pump and it's ultimate control of pressure is the
best reason I can see for using liquid fuel stoves at Philmont. To my way of
thinking the problem of getting and removing water from fuel as mentioned in
my earlier post is simple enough to outweigh the other factors.
Ounce for ounce white gas sold at Philmont contains a lot more heating value
per ounce of fuel than any other available fuel whether sold there or not.
In that respect, it is the most efficient weight wise.
Haven't I heard someone say "If you take care of the ounces, the pounds will
take care of themselves"?
On a cold, wet and rainy evening when the pot is taking a bit too long to
boil a few strokes on the pump increases the flame tremendously. That is if
your stove has a pump. It isn't so easy with a canister fuel stove.
Like I stated earlier, take your choice and pay your price. Both systems
have advantages and disadvantages. Weigh these carefully when deciding.
John LeBlanc
Eagle Class of 1959
Phirst Phil Ptrek 1959
PhilTrek 2002 630H2 Trek 16
My latest adventure was yesterday,
Today is not over yet!
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