Other people are working cooperatively on similar ideas, and I ll tell you where we are at, balancing costs, complexity, efficiency, and smoke.

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1 CMASTE Stove presentation The Kenya Stove Project Where are we and how did we get there Frank Weichman Abstract More than a decade ago I invented a light-weight, high efficiency, wood burning stove aimed at back-country hikers 1. It occurred to me at the time that the principle behind my design could save forests in deepest Africa. Stoves based on my ideas are currently being made in Kenya under the Cera-Jiko name. With a local potter, Lorris Williams here in Edmonton, who has traveled to Kenya, we are testing improved designs that can be made by artisans in the developing world using local skills and materials. Other people are working cooperatively on similar ideas, and I ll tell you where we are at, balancing costs, complexity, efficiency, and smoke. Intro To make a fire and to keep it going requires three things: fuel, air (oxygen), and a temperature high enough to support combustion. To keep a piece of wood or coal burning requires a minimum temperature. Fahrenheit 451 is the well-known ignition temperature for paper. All fires require that a piece of fuel feels other fuel around it at or above its ignition temperature. You can fool and maintain a small fire by placing the right kind of mirror around it: good insulation. An efficient cooking stove requires that the fire underneath the cooking pot concentrates the fire in the stove and minimizes heat going elsewhere. The most primitive cooking fire is an open fire with three rocks sticking up to support a pot above the fire. It scars the ground. A heat shield around the fire, often a circle of rocks, helps by keeping the cooling wind away. That limits the scar. Our design puts the fire in a ceramic pot. Ceramic has a poor heat conductivity: the mirror for the fire. Short stubby legs underneath limit the scarring. The air intake is from below and on one side, and there is a gap between the ceramic pot and the cooking vessel 1

2 above. Hereby we have solved the basic requirement: fuel is wood or charcoal, air intake, and sufficient sheltering to keep the temperature above ignition requirements. Heat that does escape from the fire heats the cooking pot. The ceramic fire pot does get too hot to touch. Improvement: In Deepest Africa the cooking pots at one time had to accommodate missionaries. Big pots require big fires. Surface area to volume ratio decreases with size of fire. Insulation becomes less critical. But, if fuel is scarce, maybe we can combine the requirements by placing a small fire pot inside a larger pot. The larger pot serves the role of the ring of stones around the campfire and supports the large cooking pot. There still is an opening for the air intake in the outer pot and a large gap below the cooking pot for the air to circulate; sorry, for the smoke to escape. In this mode the outer pot is barely warm to the touch while the fire burns brightly inside. Reality check: where there is fire, there is smoke. Where there is smoke, there is unburned fuel and on top of that there is smoke in your eyes when you cook indoors. Other efforts. From Lawrence Berkeley Labs: Ashok Gadgil <ajgadgil@lbl.gov> Fri, Jul 27, 2012 at 4:58 PM To: FL Weichman <weichman@ualberta.ca> Cc: lorriswilliams <lorriswilliams@yahoo.ca> Dear Professor Weichman, Thanks for reaching out to me. We chose precision engineered sheet metal stoves for two reasons. 1. We can build 5000 stoves per month with just a few employees while maintaining the dimensional accuracy, and integrity of the original design, and 2. Metal stoves have much lower thermal mass -- they heat up and cool down quickly, thus little thermal energy is trapped in the body of the stove after cooking is over. Lastly, you are right about the thermal conductivity of mud being lower than that of metal. However, the above

3 two issues trumped the thermal conductivity for us. We do have a stainless steel radiation shield in the stove for reducing heat transfer to the outside walls. I have not taken a close look at the details of their design and it is very likely it is efficient, cheap to make, and serves an immediate need. I read further and found that the stoves are made in India for use in the refugee camps elsewhere. Here is a reference to one of their sites: Another variant on the metal stove was designed by Payan ole MoiYoi. It is to be manufactured in Africa and as a financial contributor to his effort. I should have one of his stoves here shortly. See His design, shown above, includes air inlets high up in the stove body that encourage secondary combustion of the flue gases. That improves the burn of the available fuel and decreases the harmful smoke. We are adapting that idea in our design while encouraging him to switch from imported metal to local materials and crafts. We are also in correspondence with

4 To: "Warren T. Te Brugge" Hi there Frank, Great to hear from and hear that you are proceeding. I just returned from a trip to South Africa. There is definite interest in the village I was in, in what you are doing. I would love to hear more about progress. I am also mentoring a group in Ghana where there is an application. Warmest regards, ~ Warren This gentleman is trying to set up small local industries in the African villages he is in touch with and he is pushing hard to get more girls into education. We very much share his desire to create designs that can be produced locally. Some of the questions we have difficulty dealing with are the skills of the local potters and, more than anything else, the cost of production. Here the ceramic pot is made on a potter s wheel where a round shape is quick to make. The Kenya potters are used to extrusion methods: an outer form, an inner form, and the wet clay is squeezed into the required shape. Also, can the local fired clay stove take the heat of the cooking fire? What is the cost/benefit advantage of the double wall design? How scarce is the fuel in the target location? All in all, what more can you ask for in a STE activity?

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