[pct-l] Pepsi can stove experiments

[Brick Robbins <brick@fastpack.com>]

I've got about 10 Pepsi can stoves sitting on my window sill.

I've played with them a bunch and here is what I've discovered:

1) construction methods. Instead of drilling & cutting the cans, I've found 
that scribing and tearing is easier, faster and makes a cleaner cut. I use 
a cheap knife with a sectioned break-off blade (the edge on the knife 
makes  a big difference...), and then use a guide of some kind to stabilize 
the knife, I rotate the can, scoring it several times. I then use the blade 
to make a "starter" slit. I use my hands to tear the side wall of the can 
or I stick a screwdriver through the can bottom and pry the bottom out.

2) pinholes. I have discovered that the hole size and pattern seems to make 
a big difference. The best hole size I've found seems to be about the size 
of a sewing pin. I make the holes by clamping a pin in a pair of vice 
grips, then just pushing it into the can. Do this BEFORE you make the big 
hole in the bottom. The pattern and number of holes also makes a big 
difference. I'll take a picture of what worked best for me.

3)Fitting the two halves together. Instead of cutting vertical slits in one 
of the halves, I use my thumbnail to make several small creases in the top 
edge of the bottom can, evenly spaced. That way I can press the bottom 
can  into the top to make a tight fit, without having to worry about cuts 
tearing. I have also found that I don't need to tape the cans together this 
way because the press-fit seals the gap so that no fuel vapor leaks while 
cooking.

4) time to boil. This is greatly affected by how fast the alcohol in the 
stove heats up and vaporizes. Lots of fuel in a small stove takes a long 
time to get going. Filling the stove more than about 1/4 full really slows 
things down. If you need to use more fuel, make a deeper stove.
I discovered by accident that spilling a small amount of fuel on the 
outside of the stove REALLY speeds things up by quickly heating up the 
stove. I also discovered that the pot diameter makes a big difference too. 
For a standard Pepsi can, a pot narrower than about 6" really slows things 
down.

I've had lots of fun with this. My best so far is boiling 2 cups of water 
in 3:20.

Personally, time-to-boil is not as important to me as fuel-quantity to boil.
No matter what I do, it seems to take 30ml (about 1 fl oz) of ethyl alcohol 
to boil 500ml (2 cups) of 10C water. Can anyone make a quick calculation of 
the energy content of ethanol? What is the best possible outcome?

-Brick

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