Pocket Stove Math

by Ken Bushnell
(Olalla, WA)

I built me one of those soda pop can stoves and I was amazed at its efficiency. The first time I used it, I filled it up with the whole 2oz of fuel it will hold. Then I discovered that I could boil 2 cups of water with 1/4 oz and the fuel would last longer.

A full two ounce stove would burn for fifteen minutes while 1/4 oz. would last four thereby making the 2 oz last 30 minutes if I used it in 1/4 oz increments. 1/2 oz lasted six minutes. Since most of my cooking was either for hot chocolate, mush or coffee I was in heaven. All the hot water I wanted for just a few ounces of fuel packed in. Heck I could probably sneak it into the dogs packs, and he wouldn't even notice it.

Even better, I could test out how much fuel I'd need to carry ahead of time. I could boil some mush, hot chocolate and noodles in the back yard, before I went on a trip, and figure out exactly how much fuel I needed to carry. So to figure, one cup of alcohol, 8oz puts out about 5,000 btu. 1 btu raises one pound of water 1 degree F. Trail water from a stream might be 40 degrees F so to raise it to 212 you'll need 172 btu per pound. Since one cup of water is 8 oz, two cups equal a pound. I found only about a 30% efficiency, so I multiplied btu usage by 3 and figured I'd use about 500 btu for one pound of water, or half an oz of fuel.

However, I did notice that the stove had to be of the two oz size in order to pressurize the alcohol to get the full six minutes out of 1/2 oz of fuel. That's standard for most constructions I've seen and made. Getting fancy only seems to hamstring efficiency.

If you want more I did the math on my web site http://www.orderformcity.com/PocketStove/Adventures/math.html along with some of the field trip notes, all linked to the stove's web site at pkstove.com.


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