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chris
10-03-2002, 15:15
I'm mucking around about with alcohol stoves and have a question that I am sure at least one person on this list can answer. When building an alcohol stove, what is an optimal diameter for the fuel cup? This obviously depends on what you want to optimize and what kind of stove you are building.

Lets use a simple model: The bottom end of a can cut out. Alcohol goes in and you light it up. If Can A is a beer can, Can B is a 48 oz tomato juice can (large diameter), and Can C is a Red Bull can (small diameter), which will a) Bring water to a boil fastest, b) Bring water to a boil with the least fuel.

My guess would be that heat output will be directly related to the surface area that is available to burn. So, Can A would be the fastest and can C the slowest. But, I would guess Can A (large diameter) would be the least fuel efficient with Can C (small diameter), the most efficient.
Does this seem about right?

SGT Rock
10-03-2002, 15:34
It would be about right except that the can diameter doesn't directly relate that way to surface are of the pot that the flame contacts. In this regard the smaller one is also better. See, the burner holes go on the outside edge of most stove designs. If a large can is used, this means the flames jet out sidewaysin a larger ring. A smaller can does the same thing, but these flames start closer to the center of the pot so you get a better coverage of the flame on the bottom of the pot. A good flame spread is important, but the way the flames lick at the bottom of the pot, it is better to start that flame closer to the center and let it spread out olong the pot bottom.

DebW
10-07-2002, 14:23
I once had the idea that a larger diameter stove would be better for a larger diameter pot. So I compared a small tuna can and a can of much larger diameter and same height, both with simple fiberglass around the inside edge. Then I thought that the big can might work better with fiberglass around the outside and also a post of fiberglass in the center to put flames on all parts of the pot bottom. I tested this once, but unfortunately don't have the memory for detail of SGT Rock. I don't think it was significantly better than the small tuna can (or I would remember, right?).

dla
12-02-2007, 00:51
BTT to kill dancing bananas.

atraildreamer
12-03-2007, 18:08
I'm mucking around about with alcohol stoves and have a question that I am sure at least one person on this list can answer. When building an alcohol stove, what is an optimal diameter for the fuel cup? This obviously depends on what you want to optimize and what kind of stove you are building.

Lets use a simple model: The bottom end of a can cut out. Alcohol goes in and you light it up. If Can A is a beer can, Can B is a 48 oz tomato juice can (large diameter), and Can C is a Red Bull can (small diameter), which will a) Bring water to a boil fastest, b) Bring water to a boil with the least fuel.

My guess would be that heat output will be directly related to the surface area that is available to burn. So, Can A would be the fastest and can C the slowest. But, I would guess Can A (large diameter) would be the least fuel efficient with Can C (small diameter), the most efficient.
Does this seem about right?

The amount of fuel needed to bring a specific amount of water to a boil, in an ideal stove system, that burns with 100% efficiency, is fixed. See my article on Stove Efficiency:

http://www.whiteblaze.net/forum/showthread.php?t=19616&highlight=Fuel+efficiency

But, many variables can effect the efficiency of the burn.

If the fuel cup (can B) is too wide, it may act as a heatsink and not allow the fuel to develop enough pressure for an effective burn.

The smaller diameter can C would allow you to concentrate the heat, and would develop sufficent pressure to keep the fuel burning, but the the smaller volume of the fuel resevoir would cause a higher pressure than is desirable and cause the flames to jet out farther away from the pot/pan and waste the heat produced.

The beer/soda (can A) is probably close to the ideal diameter, IMHO, but it too can have varying efficiencies due to fuel load, height of the stove, configuration,number and diameter of the burner jets, use, or not, of a windscreen, type of alcohol used, type of pot/pan to heat, etc.

There is no simple answer to your question. Keep experimenting and find out what works best for you. Post your results. Don't burn down the homestead! :D

(Another one hooked! :banana )

Appalachian Tater
12-03-2007, 18:32
I think part of the answer depends on the diameter of the pot. Fuel efficiency if you are only using your stove once or twice a day for five or six days is not that big of a deal. The amount of wind or the temperature of the water you are boiling or the ambient temperature all probably have a larger effect than the diameter of the stove unless the diameter is either very large or small.

One thing to think about is that the area of a circle increases rapidly when you increase the diameter.