Because of the drawbacks of petroleum fueled stoves for the average backpacker, a number of people have recently turned their attention to using alcohol as a stove fuel. A search of the internet will turn up at least a dozen different do-it-yourself designs as well as several products that are commercially available. Some of these designs are little more than shallow, open cans, some are dangerous fire hazards. Others are fairly ingenious and incorporate some good ideas. But none of these are really stoves. They are alcohol burners, which is only one part of a complete stove. To understand the difference between a simple burner and a true stove, it is first necessary to understand the process of combustion.
Combustion is a chemical process that occurs when oxygen atoms excited by heat energy bond rapidly with certain fuel elements. The most common fuel sources are hydrocarbons and related organic molecules. These are molecules that are made up primarily from hydrogen and carbon atoms. Methane (natural gas), gasoline, kerosene, propane, butane, methyl alcohol and ethyl alcohol are all examples of hydrocarbons and related compounds. The hydrogen and carbon atoms in these molecules are the actual fuel in the combustion process.
Oxygen atoms have a very strong tendency to bond with both hydrogen and carbon atoms. In fact oxygen's potential to bond with both hydrogen and carbon is so strong that it literally rips apart the hydrocarbon molecules and forms new compounds. When two oxygen atoms bond with a carbon atom, the result is CO2, carbon dioxide. When one oxygen molecule bonds with two hydrogen molecules, the result is H2O, water. Water and carbon dioxide are byproducts of the combustion of any hydrocarbon fuel. Because the process of forming these molecules produces heat (an exothermic reaction), these gasses incandesce, which means they glow or give off light. These glowing gasses are what make up the flame.
You might see from this discussion that for any specific fuel molecule there is some amount of oxygen that is "exactly right" in order to enable complete combustion. This is called the Stoichiometric ratio. This ratio varies depending on the number of hydrogen and carbon atoms in the fuel molecule. For example propane, C3H8, has three carbon atoms and eight hydrogen atoms. As each carbon atom needs two oxygen atoms, and every two hydrogen atoms need one oxygen atom, one molecule of propane needs five oxygen molecules (oxygen occurs in nature as a diatomic molecule O2, so five molecules provide ten atoms). This is usually written as a reaction formula:
C3H8 + (5)O2 --> (3)CO2 + (4)H2O
If there is not enough oxygen available for complete combustion, some unburned fuel will escape and its energy will be lost. Usually this takes the form of carbon monoxide being formed in place of carbon dioxide.
It might seem that the best solution to the problem of incomplete combustion would be to insure there is extra oxygen, more than is needed for the Stoichiometric ratio of the fuel. All this extra oxygen would pretty much insure that there was always some available when it was needed. Unfortunately, this causes another problem which is called "excess air". Since air is mostly nitrogen, which doesn't contribute to the combustion reaction, adding even a little bit too much oxygen adds a lot of extra nitrogen. This extra air takes heat away from the flame, causing it to be cooler and less stable.
You can see this for yourself with an oil lamp. Light an oil lamp, but leave the chimney off. Watch the flame. Notice that the flame color is a dull yellow and that the flame is narrow and long, and may change size and shape as it burns. Now put the chimney on. The character of the flame immediately changes. The color goes from a dull yellow to a bright, incandescent yellow-white. The shape of the flame changes from being long and narrow to rounded and compact. It is also a steady flame with less tendency to flicker. But the big difference is the amount of light. Without the chimney, much of the energy in the burning oil was lost in heating up the surrounding air. With the chimney, this energy is available to produce light.
Let's look at another example. Anyone who heats their house with wood knows that there is a tremendous difference between the performance of a fireplace and a wood stove. Wood stoves put out much more heat and require a lot less fuel. A fireplace may look nice and homey, but it just isn't practical for heating. Since both are basically boxes that you build a fire in, why should there be such a difference in performance? One possibility is that the stove sits out in the room and can radiate heat in all directions. But free standing fireplaces are even less efficient and put out less heat than the built-in kind, so that can't explain the difference. The real reason is that stoves are built air tight, with carefully designed ports that control the quantity and direction of the air that's allowed to react with the fuel.
If you have managed to make it this far, you are probably figuring out where this is going. To make a stove, it is not enough to simply get fuel to burn. You could put a kerosene soaked rag into a can and light it. It would burn and you could contrive a way to boil a pot of water with it, but it wouldn't be a stove. A stove requires some way to control the proportion and mixing of the fuel and air to produce a hot, efficient, consistent and controlled flame.
Petroleum fueled stoves solve this problem with an assortment of pumps, valves, nozzles and orifices. The fuel and air are mixed together when they are cold to achieve the proper Stoichiometric ratio. This fuel/air mixture then moves to the burner, where the temperature is hot enough to ignite it. This type of flame is called a "premixed flame".
What is it that makes the ThermoJet MicroLite so superior to simple alcohol burners that it can offer performance comparable to gas fueled stoves? It operates on a completely different principle from ordinary stoves. It works like a little jet engine (although it is completely silent). Every part of it is precision engineered to get every bit of available energy from the fuel to the cooking pot. The burner itself is extremely efficient. It is made from aluminum, which is lighter and has superior thermal characteristics to either steel or brass. The burner also has a much smaller surface area than other aluminum burners, such as those that are made from pop cans. A smaller surface area means that less heat is lost from the burner. These factors come together to create a burner that stays hotter without the mess and fire hazard of an open "preheat tray" that engulfs the entire burner in flame. Compare the flame from the ThermoJet MicroLite's burner with other alcohol burners. The ThermoJet MicroLite burns steady and pale blue indicating a hot, efficient flame. Other products burn with a cold, inefficient, yellow flame.
The burner on the ThermoJet MicroLite has a double chamber design that makes it easy to use without sacrificing combustion efficiency. The burner is filled through the large, open, center well. From there the fuel flows into the outer chamber where it is sealed by the fuel below it. It's that simple; no special fuel bottles, no funnels, no measuring cups, no plugs to loose, no lids to fiddle with, no dangerous preheat trays that need more fuel and create a fire hazard. As the fuel in the center well burns, it heats up the burner and causes the alcohol to boil. The fuel in the outer chamber vaporizes and is forced out through the orifices in the top of the chamber. These jets of superheated alcohol vapor ignite when they come in contact with oxygen in the air. This is called a "diffusion flame". Because the ThermoJet MicroLite burns with a diffusion flame, it avoids all the complexity associated with a petroleum stove.
The pressurized fuel jets are another design feature central to the efficiency and high temperature of the stove. As the jets of alcohol escape from the orifices, they create a low pressure area due to an effect called the Bernoulli principle. This actively sucks air into the vapor streams where the turbulence caused by the high fluid velocity ensures thorough mixing of the fuel and air. In addition, the size and shape of the burner are specifically designed to promote the efficient fluid flow and mixing of the fuel and air.
The advanced design of the burner is just the beginning of what makes the ThermoJet MicroLite work so well. As we saw above, a true stove must control the air flow as well as the fuel flow. Otherwise the burner is like the oil lamp without a chimney, or an inefficient fireplace. The ThermoJet MicroLite achieves this air flow control through the use of its unique combustion chamber. Although it may look like a windscreen (and will serve this purpose under moderate conditions), that is not its main function. The combustion chamber is designed with engineered metering ports that precisely control the amount of air that reaches the fuel. This insures the correct Stoichiometric ratio of air and fuel, producing the hottest possible flame and high heat transfer to the cooking pot.
The combustion chamber also allows another innovation that no alcohol burner can match - an integral, external simmer control. Unlike impractical designs that use a separate part that you have to try to set on top of the flaming burner (ouch!) or require that you remove the pot to get at the adjustment, the simmer control of the ThermoJet MicroLite is on the outside of the combustion chamber. No more burned fingers, no more juggling pots! Simply slide the simmer control over the main ports and the simmer ports are automatically opened. Almost instantly, the stove changes from a rolling boil to a steady simmer. Best of all, it really works - even better than adjustments on many liquid fuel or canister stoves which can vary significantly as the fuel pressure changes. This design also eliminates hot spots, allowing faster and more even cooking without scorching.
Putting all these advanced features together results in the ThermoJet MicroLite, the first and only true, alcohol fueled stove available anywhere. Finally, backpackers have a real alternative between bulky, heavy petroleum stoves and eating cold meals. What's more, the ThermoJet MicroLite comes complete with everything you need. Just add some fuel and your pot and you'll be cooking!