Design Princples for Wood Burning Cook Stoves

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Chastity Ward
6 years ago
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1 Design Princples for Wood Burning Cook Stoves

2 The Dr Winiarski Rocket Stove Insulated low mass combustion chamber Internal shelf allows sticks to form a grate. Stick/air/stick/air Small amount of high velocity air is drawn under the coals and the wood grate which improves air to fuel mixture Stove power is controlled by regulating the fuel supply not the air intake Horizontal feed chamber is convenient

3 X Basic Rocket Stove Geometry 1.5-2X Total Height = X + (1.5Xor2X) + 5 cm X Min 2x

4 One Whenever possible, insulate around the fire using lightweight, heat-resistant materials. Insulation around the fire keeps it hot which reduces smoke Insulation around the fire keeps the heat from going into the stove body instead of pot

5 One (Cont ) If possible, avoid heavy materials like sand, clay, and cement. Metal is better than heavy material above (less thermal mass) but does not last very long near hot fire. Heat resistant insulated material are best

6 Two Place an insulated short chimney right above the fire. a short insulated chimney right above fire forces mixing of flames and smoke which burns up the harmful smoke. The short chimney above the fire increases the speed of the air drawn into the fire which helps the fire to burn hotter. Forcing the hot gases to scrape past the pot at a high speed helps to heat up the food more quickly while using less fuel.

7 Three Heat and burn the tips of the sticks as they enter the fire. If only the wood that is burning is hot there will be much less smoke. The goal is to make the proper amount of gas so that it can be cleanly burned without making charcoal or smoke.

8 Four High and low heat are created by how many sticks are pushed into the fire. Adjust the amount of gas made and fire created to suit the cooking task. (Wood gets hot and releases gas. The gas catches fire and makes heat.) Low Heat High Heat

9 Five Maintain a good fast draft through the burning fuel. Just as blowing on a fire and charcoal can make it hotter, having the proper amount of draft will help to keep high temperatures in your stove. A hot fire is a clean fire. The wind passing through the coals helps to raise the temperature of the fire so that all the gases become flame.

Six Too little draft being pulled into the fire will result in smoke and excess charcoal. If a lot of charcoal is being made by the fire then there is too little air entering the combustion chamber.

10 Six Too little draft being pulled into the fire will result in smoke and excess charcoal. If a lot of charcoal is being made by the fire then there is too little air entering the combustion chamber. A fire that makes a lot of charcoal is producing too much harmful carbon monoxide. A hot clean burning fire will not make much charcoal as it is being used. Make sure that enough air is freely flowing under the fire into the coals

11 Seven The opening into the fire, the size of the spaces within the stove through which hot air flows, and the chimney should all be about the same size. This is called maintaining constant cross-sectional area Good draft not only keeps the fire hot; it is also essential so that the hot air created by the fire can effectively transfer its heat into the pot. Air does not carry very much energy, so a lot of it needs to go through the stove in order to accomplish the task of heating food or water.

12 Eight Use a grate under the fire. Do not put the sticks on the floor of the combustion chamber. Air needs to pass under the burning sticks, up through the charcoal, and into the fire. A shelf in the stove opening also lifts up sticks so air can pass underneath them.

13 Nine Insulate the heat flow path. If the heat goes into the body of the stove, the pot boils less quickly. Using insulative materials in the stove keeps the flue gases hot so that they can more effectively heat the pan

gap too large: hot flue gases mostly stay in the middle of the channel and do not pass their

14 Ten Maximize heat transfer to the pot with properly sized gaps. Getting heat into pots or griddles is best done with small channels. gap too large: hot flue gases mostly stay in the middle of the channel and do not pass their heat to the desired cooking surface. Gap too small: the draft diminishes, causing the fire to be cooler, the emissions to go up, and less heat to enter the pot.

15 Optimising heat transfer Maximize the surface area where the hot flue gases touch the pot

16 Rocket stove heat exchanger/skirt Ensure the correct gap between the pot and the stove body (for average household pots, 7-10 mm is good rule of thumb) Make the skirt as tall as feasibly possible

17 Gap D Gap A Gap B Gap C

chamber) Perimeter of outer feed chamber = [(D+10 cm] *3.

18 Gap D Gap A Gap B Gap C To calculate gap A ( between the top of the combustion gap A = Area of feed chamber chamber and the pot) Perimeter of feed chamber To calculate gap B ( between the pot and the gap B = Area of feed chamber outer edge of the combustion chamber) Perimeter of outer feed chamber = [(D+10 cm] *3.14) To calculate gap C (under the outer edge of the pot gap C = Area of feed chamber and the stove body) Circumference Pot To calculate gap D (between the sides of the pot gap D = gap C * 0.75 and the stove body)

19 Pumice insulation Can calculate density (g/cc) or test to see if the mixture floats. Yes? Then less than 1 g/cc A very light insulative mixture 4 g/cc (ideal for top plate).6 -.8g/cc ideal for combustion chamber above abrasion points ( i.e above feed chamber)

20 Move to Stove Performance Test

Images/Logos. Five Tier 4 Stoves Move Towards the Market. Dean Still. DOE BETO Cookstoves Program Review

Images/Logos. Five Tier 4 Stoves Move Towards the Market. Dean Still. DOE BETO Cookstoves Program Review Five Tier 4 Stoves Move Towards the Market Images/Logos DOE BETO Cookstoves Program Review Dean Still Aprovecho Research Center Beijing University of Chemical Technology January 23, 2015 University of