A rocket stove is a simple type of cook stove that is specifically designed to be used in under-developed areas. They burn fuel more effectively and more cleanly than a normal cook fire, and they can be made from easily acquired materials. It was designed by Dr. Larry Winiarski, the Technical Director of the Aprovecho Research Center for appropriate technologies, and are now used the world over.
Rocket stoves can be made out of bricks, stone, clay, and/or sheet metal, depending on what is locally available. The basic structure of a rocket stove is a small insulated combustion chamber, open at the top with some sort of support for a pot. At the base of this chamber there is a fuel magazine, a short entry passage to put fuel into the combustion chamber. Within the fuel magazine there is a shelf to raise the fuel off the floor of the magazine. And that's it.
Here's why all of that is so important. The shelf in the fuel magazine keeps the fuel (usually sticks and twigs) off the ground; this shelf is literally a shelf, raised off the ground so that air passes below. Once the stove starts to draw, the cooler outside air is drawn in under the fuel shelf; this allows the air to be preheated before it enters the combustion chamber, allowing for more complete combustion. Likewise, because the fuel is elevated it isn't suffocated by ash, allowing for a hot, clean burn.
Moreover, the small, insulated combustion chamber means that heat is concentrated around the burning fuel, increasing the efficiency of combustion. Because the chamber is small, the fuel can only be pushed in a little bit at a time, meaning the fuel is only burned as needed.
So, we have a small but efficient stove that burns hot and cleanly (little carbon monoxide and particulate matter), and uses a minimum of fuel. But it gets better. The combustion chamber is right below the cooking pot, and the top of the combustion chamber should fit the pot so well that the flame has to wrap around the pot as the heat is drawn up through the stove. This effect can be increased by adding a 'pot skit', a pot-deep rim added to the top of the combustion chamber so that the hot air coming from the stove is forced to travel right up against the sides of the pot. This results in as much heat energy as possible to be transferred to the food.
Why is all of this important? Well, traditional cooking fires (often called three stone fires, because the consist of a pot set on three stones over an open fire), use much more fuel and don't direct the heat so well. In many parts of the world fuel, in the form of wood, is in short supply, or will soon be in short supply if we continue to use it at the current rate. Using rocket stoves, which can burn twigs and sticks effectively, help prevent deforestation and desertification.
Traditional fires also give off a lot of nasty smoke and gasses, which can lead to many bad things, from asthma to lung cancer. This is particularly important indoors, which has led to an indoor modification of the rocket stove called the justa stove, which has a smokestack and a griddle-type stove top.
While rocket stoves and justa stoves are used all over the world, if you live in America you may have heard something else referred to as a rocket stove. Ianto Evans developed something he calls a rocket stove, AKA a Ianto-style rocket stove or a rocket thermal mass heater. This is a modified heater made from a 55 gallon drum that is often used for heating cob houses. While it can be used for cooking to some extent, it is actually a cleverly designed thermal mass heater.
has a good video describing the construction of a basic rocket stove.
Yet another entry to Wintergreen: An Earth Quest.