[Stoves] Shape of charcoal burners. Was Re: charcoal ProContra wood fuel

[Paul S. Anderson]

Quoting Crispin Pemberton-Pigott <crispinpigott at gmail.com>:

> I found that the combustion chamber should be conical in shape and have an
> included angle of 135 degrees, not flat like a JIKO. This causes the
> charcoal as it burns to keep moving together to maintain the fire. On a flat
> surface the pieces cool and burn out individually, but it they are always
> falling towards each other, the stay lit much longer so you don't have to
> add fuel as often.

Crispin,

Very good observation, and I believe you have incorporated that into 
one of your
stoves.  Is that in the Maputo Cermaic Stove (MCS)?

How did you arrive at the 135 degree angle?  That would be with the top angled
out 67.5 degrees from the vertical center line, right?  Trial and error or
calculations or both?

The amount of heat/combustion of the charcoal is related to the air 
reaching the
hot (that is, already ignited) char layer.  Is all of the char hot and burning
or is it only the part closest to the air entry hole that is in the center of
the bottom?

Rising air will not easily go 90 degree laterally to the sides of a 
flat bottom.
Not will it rise only straight upward.  Instead it will take a path in conical
shape.  But is that really a 135 degree included angle?  Has much research on
this been done?

Of course, the size of the pieces of charcoal might also have some 
impact on the
best angle.   And also on the ability of the char pile to fall into the spaces
created by the combustion.

Paul


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