[Stoves] ash layer beneath fire

Dr.-Ing. Dieter Seifert doseifert at googlemail.com
Thu Jan 23 06:21:17 CST 2014


Dear Crispin, Richard and Vincent,

I should like to make some remarks regarding the practice in the use of 
a stove with a grate fuelled with thin sticks or appropriate pellets:

The lighting is greatly simplified if one places igniting paper in the 
form of three or four rolls, crosswise to the steel bars. One can then 
ignite the paper rolls (with the kinlding on them) from the heating 
port, after having already inserted the pot. The smoke-phase is then 
short and heat loss is reduced.

With experience one can ensure that the insertion of the sticks is 
stopped in time, so that the sticks burn completely and the pot contents 
are parboiled - but the cooking is finished in the thermos-container 
(haybox, haybasket) as mentioned earlier. The wood consumption may be 
330 g (corresponding to 5 MJ of heat content) for cooking 6 kg of food 
(requiring theoretically about 1.9 MJ heat supply). Thereby a little ash 
(about 2 g) is produced.

This method reduces the stress on the cook. A consumption of charcoal of 
more than 1.3 tons per year (more than 8000 kg chopped tree weight) by a 
household is reduced to about 600 kg of thin sticks, moreover with more 
comfort for all involved and less health burden.

I believe that this technology is in the sense of E. F. Schumacher that 
is promoted exemplary through Practical Action.

With kind regards

Dieter


Am 22.01.2014 23:51, schrieb Crispin Pemberton-Pigott:
> Dear Richard and Vincent
>
>   
>
> Jambo.
>
>   
>
> I see just about everyone found that adding a grate to a flat-bottomed stove
> improves the performance.
>
>   
>
> RS>.I would advise use of round bars as Crispin but I would suggest you
> grind any round bars down to result in effectively a series of had cylinders
> along their length with the flat side up.
>
>   
>
> I would advise the opposite and the metric to use in evaluating the
> difference is the mass fraction of charcoal produced by the fire. We found
> (for reasons that are not yet known) having a flat top definitely produces
> more char thus losing more heat. It may have something to do with the
> thermal contact the char piece makes with the metal, conducting the heat
> away. This lowers the temperature of the 'coal' and causes it to burn poorly
> or go out. There was a large mass difference for flat and round bars - more
> than double.  The thermal contact between a coal and the round bar is much
> smaller.
>
>   
>
> That is the only 'guess' I have so far. We will look into this further at
> YDD this year. The two things tried were round bars from mild steel
> (multiple welded pieces) and cast iron with a flat top (single piece). Cast
> iron conducts less heat than mild steel but it still consistently produced
> much more char. That is not useful as fuel in most homes and it is tossed
> with the ash. Indar reported the round bar grate produced virtually no char
> at all, finishing its burn at virtually the same time as the wood. That was
> amazing.
>
>   
>
> You may need to restrict the air entry area to limit the air level below the
> combustion chamber. If it is 'right' you will see large flames wandering
> around in a low velocity environment below the pot - no flapping arms of
> flame.  You should limit the pot gap (by shaping those tongues of clay) to
> about 7mm for all pot sizes. This means trimming the slanted ones and
> lowering the top ones (in most stoves).
>
>   
>
> The combination gives you the right balance of primary and secondary air.
>
>   
>
> Nzuri kuhusu
>
> Crispin
>
>   
>
>
>
>
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