Dear All, I spent some time recently with Servals team in developing a low cost improved traditional woodstove - and the result was good.
Basically a traditional looking stove ( a 4 litre metallic container converted ) - clay lining ( can be changed over to refractory or stainless steel ), flame concentrator at the top ( similar to TLUD stove ), air pipe ( metallic, around 12" long ) at the bottom. The flame concentrator has two functions ( as we all know ) : 1. Better mixing of combustion air with the woodgas - for a more complete burn. 2. Brings the flame to the centre of the cooking pot bottom. The air pipe ( horizontally placed ) brings a small quantity of air below the burning wood mass at the centre. This air burns a little quantity of charcoal, keeping this area intensely hot - this also keeps a stable flame throughout. Since the pipe is metallic, this air gets preheated ( inside the pipe ) before it reacts with charcoal. We can imagine what pre-heated ( upto around 300 C ) air can do to an already burning charcoal mass. We also tried a grate at the stove bottom ( instead of the air pipe ). But the result was not good. Air pipe has the advantage of pre-heating the air and also allowing only a controlled quantity of air in. Some perforations near the hot tip of the pipe adds to the performance. It takes about 10 minutes for the air pipe to start functioning - ie. when the stove bottom ( inside ) gets heated up sufficiently to create a suction through the pipe. The cross-sectional area of the air pipe can be around 10 % of the cross-sectional area of the fuel-window ( through which the fuel is fed in ). For an average domestic stove, 1 1/2" dia pipe should be ideal. The flame concentrator and the air pipe can be an add-on to any traditional woodstove - including a three stone fire. Especially the air pipe is a valuable add-on with negligible cost involved. The small stove we tested had a fire-power of around 3 KW ( average around 2 KW ). The flame looked almost as good as a TLUD stove ( ND ) flame. The fire-power can be easily upgraded for larger versions of the stove. Flame control is like in any trditional stove ( withdrawing the burning wood ). With Best Regards, Rajan
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