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[pct-l] Fuels

Wow!  The first time I've ever been able to use my background as an
energy economist to answer a hiking question.  Here goes.

You asked which produces more heat: wood, charcoal, or petroleum-based
fuels.  First, your chemical expressions for each fuel requires a slight
adjustment.  Wood is more than just carbon and water; it also contains
lots of volitiles (carbon/hydrogen compounds) and inert matter.  For
example, pine tar and turpentine is extracted from wood.  When you burn
wood you get a significant amount of ash; this is the inert material
that doesn't burn.

Charcoal is a lot more than just carbon.  Commercial charcoal briquettes
contain a lot of binder (like wax) and about 25% ash (more inert
material that doesn't burn).  I last looked at charcoal chemically about
8 years ago, and I think it was 10% binder, and about 25% ash, plus
about 50% carbon, plus a bunch of ignition helpers and aroma makers.
Pure carbon is very hard to light, and can stink (because of very small
amounts of sulfur that are hard to remove, so they just cover them up
with other smells).

There are several petroleum fuels that I've seen used on the trail:
butane, white gas, and gasoline.  Butane is kept in a pressurized
container because it is a gas at room temperature.  Per unit of fuel
weight it has the lowest Btu content of the three.  It is also the
heaviest per Btu in total weight because the pressurized container is
heavier than the standard fuel bottles used for the other two fuels.

White gas is actually the chemical naphtha.  It is sold in a fairly pure
form for use in camper stoves.  Naphtha has a greater heat content than
butane because it is more complex (has more chemical bonds to break when
burned).  The primary use for naphtha in the U.S. is a blending stock
for gasoline (it makes up about 50% of every gallon of gasoline).  Hint:
Instead of letting your white gas get old in your fuel bottle between
seasons, just add it to your gas tank when you buy gasoline.  No harm
will come to your car.

Gasoline is a mixture of many chemical compounds, including (surprise)
naphtha, butane, isobutane, propane, various pentanes, benzene, alcohol
and other petroleum derivatives.  The mixture is often regulated by
state and federal clean air laws (California's being uniquely
restrictive, compared to the other 49 states).  These regulations can
lead to much cleaner air (hurray).  Most of these compounds have less
heating value per pound than white gas.  

My guess is that the difference in heating value between gasoline and
white gas is so low as to be unnoticeable to most hikers.  You would
notice more fuel consumption efficiency if you just let your cooking
water heat up to air temperature before using, rather than selecting
white gas over gasoline.  Butane requires heavy duty containers, which
make it unattractive.  Wood and charcoal have other stuff which reduces
their Btu content.  Besides, you use wood because its there on the
trail, not because you want to carry it many miles. And who would want
to wait for a charcoal fire to heat up a pot of water, and then waste
the charcoal as it burned down?

In the 7,000 miles of hiking I've done, I've always used white gas in a
Whisperlite stove.  For reasons too lengthy to get into here, it used to
clog the fuel jet when used at higher altitudes (say 10,000 feet), but
the new shaker jet has taken care of that problem.  Another hint: To
keep your stove jet clean, blow out the flame before the fuel burns down
all the way.

One final note on safety: I saw a hiker seriously burned in the crotch
area when he accidentally spilled on himself, and then ignited, less
than tow ounces of stove fuel.  He received third degree burns over a
very large and painful area, which later required a doctor's attention
and expensive medication.  This was a very experienced hiker, so don't
say it can't happen to you.  Please be careful out there!
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