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Tuesday, November 1, 2011

DIY Alcohol Stove Design

Original Article

This is an article from Wikipedia describing the function and design of the diy Trangia-style alcohol stove that is commonly made from aluminum drink cans. I have seen these designs all over the 'Net, and have built a few of them myself. Most of the articles I have seen simply give step-by-step instructions for building a stove. This article doesn't give building instructions; it rather explains how and why the design works, and compares different versions of the stove. 

Beverage-can stove

From Wikipedia, the free encyclopedia

Beverage-can stove (the pot stand is omitted for clarity)
A beverage-can (or pop-can) stove is a homemade, ultralight portable stove. The simple design is made entirely from aluminium cans and burns denatured alcohol. Countless variations on the basic design exist.
Total weight, including a windscreen/stand, can be less than one ounce (30 g). The design is popular with ultralight backpackers due to its low cost and lighter weight than most commercial stoves. This advantage may be lost on long hiking trips, where a lot of fuel is packed, since alcohol has less energy per weight as some other stove fuels.

History and design

The basic design dates back more than a century. It consists of a double-wall gas generator, a perforated burner ring, and an inner preheat chamber. A similar design was patented in 1904 by New York coppersmith J. Heinrichs. Trangia has been selling a commercial version of the design since 1925, and Safesport marketed a stainless-steel stove in the 1990s. The Trangia stove burner is made from brass, although all the other associated parts that come with it are aluminium. A plastic bag is provided for the burner, so that when packed away the two dissimilar metals do not corrode.
In the unpressurized open-top design the double wall acts as a gas generator, transferring heat from the flame to the fuel. This effect enhances combustion, producing more heat than other passive designs. The inner wall also creates a convenient preheat chamber for starting the stove. Once the fuel has warmed up, its vapor will travel up the hollow wall, pass through the perforations, and form a ring of flame. This improves air/fuel mixing and therefore combustion. Vapor also rises from the center of the stove, but will pass through the ring of flame for efficient combustion as long as a pot is over the stove. Other pressurized designs aim for efficient combustion through closing the fuel chamber after filling, or by filling through the gas-jet holes.
A wick may be inserted into the hollow wall, where it will draw fuel upwards closer to the hot parts of the burner. Evaporating fuel from the wick removes heat from the top parts of the burner and subsequently the fuel at the bottom receives less heat. This slows down evaporation through the center while increasing the gas pressure inside the wall, spreading the ring of flame outwards while the center of the burner produces almost no flame, leading to a more controlled burn and faster starting. Suitable wick materials include fiberglass or cotton cloth. The wick will not burn because the evaporating fuel keeps it cool, and the pressure inside prevents air from entering the hollow until the burner can no longer produce enough gas to support a flame.



Fuel is poured into the stove and ignited, burning in the center.

The flame heats the fuel and interior of the stove, causing the fuel to vaporize.

When the temperature is high enough, vapor pressure causes fuel jets and a ring of flame.

Aluminium-can construction


Three-piece beverage-can stove (exploded view).
The stove is made from two aluminium can bottoms. An inner wall is cut and rolled from the can material. A ring of holes is pierced into the top with a pin. Parts are glued with high-temperature epoxy, or sealed with thermal foil tape, although this is not strictly necessary. Total height is less than two inches (50 mm), though dimensions may be increased to hold more fuel or decreased to take up even less space.
The choice of aluminium has several advantages—light weight, low cost, and good thermal conductivity to aid vaporization of fuel. Alternative construction materials have been used, including stoves made of tin cans such as cat food tins, tuna cans, and juice cans—the basic design is very similar. Windscreens/stands can be fabricated from tin cans, cut to size with ventilation holes added.

Operation and performance

Each stove is designed for one or two people. When used to cook larger meals (greater than 2 cups (0.5 litres)), it is less efficient than a more-powerful stove which delivers more heat to a pot. This is because a longer cooking time is required, during which more heat is lost to the surroundings. A more powerful, pressurized version is shown below.
To use the stove, a small amount of fuel is poured into the stove and ignited. The pot is then placed above the stove, on a windscreen or stand. The flame is small at first, only burning from the inner chamber. Once the fuel has warmed up (requiring about one minute) its vapor will pass through the perforations and form a ring of flame. Enough heat from the flame is passed to the fuel to maintain full combustion until the fuel runs out.

Ratings

  • Time to boil 2 cups (500 ml): ~12 minutes (45 ml of fuel)
  • Time to boil 4 cups (1 l): ~24 minutes (90 ml of fuel)
  • Burn time: ~16 minutes (60 ml/4 tablespoons of fuel)

Comparison with other stoves

The stove can outperform some commercial models in cold or high-altitude environments, where propane and butane canisters might fail. Roland Mueser, in Long-Distance Hiking, surveyed hikers on the Appalachian Trail and found that this stove was the only design with a zero-percent failure rate.
Fuel usage (by weight) is about fifty percent greater than a butane/propane stove. Can stoves weigh less than an ounce, compared with three ounces for the lightest gas stoves. Many commercial stoves also require special fuel canisters, adding to overall stove weight. No such canisters are necessary in a can stove; denatured alcohol can be carried in virtually any lightweight container, such as a plastic soda bottle. The weight advantage of the beverage-can stove is diminished by the greater fuel consumption (especially on longer hikes), but may still be offset by its reliability and simplicity.
Other attributes of the beverage-can stove are its nearly silent operation and its suitability as an emergency backup. Denatured alcohol is a (relatively) environmentally-friendly fuel that does not leave a residue of soot, although it is toxic to drink. (Pure ethanol is rarely used as stove fuel in the United States, since it is usually subject to a liquor tax.) Denatured alcohol is commonly available at camping outfitters and hardware stores. These stoves operate marginally on 90% isopropyl alcohol, poorly on 70% and not at all with 50%. Water typically can not be boiled with isopropyl.
Unsealed alcohol stoves are inherently dangerous, since spilling is possible and the fuel burns with a nearly invisible flame. Trangia offers an anti-flashback fuel bottle with an auto-shut-off pourer. If a spill occurs the best course of action is to step back and let the alcohol burn up.

Variations


Beverage-can stove variations with cross sections in yellow. From left to right—standard design; inverted two-piece; side-burner; pressurized.

A side-burner stove built from a single can as part of a Scouting project.
Standard 
The classic ultra-lightweight backpacking stove. Designed for one person, lighter than commercial models of the same design
Inverted two-piece 
Smaller and lighter than the standard version; difficult to fill
Side-burner 
Doubles as its own pot stand (holes are in the side). A tight-fitting pot can increase fuel pressure
Pressurized 
A more powerful version, but heavier and more difficult to make. The stove is sealed with a thumbscrew after filling with fuel; this allows the stove to control the rate of heat output. An additional base is used to hold fuel for preheating
Back-Pressured 
Back-pressured stoves simplify the pressurized design by eliminating the thumbscrew and the base needed for preheating, while still controlling the rate of energy output
Insulated 
A variation on the standard design, with an inner wall and insulated with fiberglass
Other 
Numerous designs in use
Multiple-unit 
When cooking for a larger number of people, nothing prevents the use of more than one unit under the same pot

Safety issues

The Boy Scouts of America now prohibits "equipment that is handcrafted, homemade, modified, or installed beyond the manufacturer’s stated design limitations or use. Examples include alcohol-burning 'can' stoves, smudge pots, improperly installed heaters, and propane burners with their regulators removed."

See also


Notes

  1. ^ U.S. Patent 560,319: W.J.D. Mast (1895)
  2. ^ U.S. Patent 766,618: J Heinrichs (1904)
  3. ^ Robinson, Roy. "The Cat Food Can Alcohol Stove". Retrieved on March 17, 2007.
  4. ^ Mueser, Roland Long-Distance Hiking: Lessons from the Appalachian Trail (1997)
  5. ^ "Weight comparison of beverage-can stoves vs. some commercial stoves"
  6. ^ http://www.scouting.org/filestore/pdf/680-013WB.pdf BSA Policy on Use of Chemical Fuels. Accessed January 22, 2011.

References

External links

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