The Rocket Stove is the application of pure thought to solve a problem that affects the health and lives of about one third of the world’s population.
Smoke from cooking fires kills two million persons per year, mostly mothers and small children. Stoves and open fires are the primary means of cooking and heating for nearly three billion people. In India, some 400,000 people die each year from the toxic fumes. In Africa, 500,000 children under the age of five die from pneumonia attributable to indoor air pollution, according to the WHO. Most of these deaths are attributable to cooking indoors over a three-stone cooking fire.
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For over 30 years, Aprovecho Research Center (ARC) consultants have been designing and implementing improved biomass cooking and heating technologies in more than 60 countries worldwide. The Center was formally established in 1976, and is dedicated to researching, developing and disseminating clean cookstove technologies for meeting the basic needs of refugees, impoverished people, and communities in the developing world. For decades, ARC has been the world’s leader in open source development of all aspects of improved cooking stoves.
Dr. Larry Winiarski works for the Aprovecho Research Centre. He’s known as the inventor of The Rocket Stove but it’s more correct to say he identified the principles that a Rocket Stove makes use of to work as efficiently and elegantly as it does .
- Air flows in from the fuel intake and is pre-heated for better combustion
- The fuel partially blocks the air intake, allowing for a better fuel/air ratio.
- The intake air is preheated for more efficient combustion.
- Fuel burns horizontally at the bottom of the combustion chamber. Any smoke is drawn upwards through a high temperature zone, ensuring more complete combustion.
More complete combustion means less smoke.
- The stove can burn relatively green wood. Moisture near the surface of the wood turns to steam that, when it comes into contact with hot charcoal, forms CO and H2 which are both combustible. Their combustion reaction further increases the temperature of the high-temperature zone, to ensure even more complete combustion, and even less smoke. Dr. Winiarski explains the mechanisms of combustion and heat transfer in this paper.
“One of the first things to recognize is that solid or liquid material does not burn directly. It must be converted to gasses in order to burn. Most biomass is hydrocarbons which, when heated convert to oil and oil vapors of many different types. Some oils such as fragrances, turpentine are visible or smelled even before the biomass is heated. Green, wet wood may contain as much as its dry weight in water and, in order to burn water, must be evaporated. Up to about 1000 BTUs of energy is used to evaporate each pound of water. At sea level and atmospheric pressure, the temperature of boiling water is limited to 212 degrees fahrenheit.
“Similarly heat energy must be provided to evaporate or distill each of the hydrocarbons formed from the wood. The lighter hydrocarbons are easier to change to the gas phase, heavier hydrocarbons like creosote take more energy, however if too much fuel surface is heated and the gases cool before they can intermingle and ignite with hot air or oxygen they will condense back into a fog our cloud of oil droplets. This is the smoke we see. It is analogous to the fog or cloud that forms when water vapor condenses. Heat must re-evaporate the oil droplets before they can burn. After the many different types of oils are combusted only charcoal remains. The hot charcoal first reacts with oxygen to form gaseous carbon monoxide. Then the carbon monoxide burns with the air to make carbon dioxide. Carbon dioxide is the final result of a clean burn. Smoke and carbon monoxide are wasted fuel.”
- Twigs and other types of low-grade wood scraps not normally classed as firewood have a proportionally larger surface area to supply fuel for these reactions.
Low-grade scrap wood works better than high-grade firewood.
- The horizontal burning of the wood allows for better monitoring and tending.
- The stove can be designed to have an angled gravity feed.
- Variations can be made to have a secondary heating “element
- The flue can be vented through a thermal mass element that functions as a heat storage device for space heating.
The stove can be made for practically nothing.
- You can make one yourself out of three cans.
- Four concrete blocks.
- About 30 bricks.
- You can make a rocket-stove inspired architectural feature if you like.
- But, judging by the size of that air/fuel opening and the type/size/shape of fuel, it won’t function as efficiently one made of mud and using twigs for fuel.
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Dr. Larry Winiarski & The Aprovecho Research Center
for having an idea for an object that’s as perfect as an object can be
and for releasing it to the world to be used wherever it brings benefit