[Stoves] Charcoal & Stoves

[Crispin Pemberton-Pigott]

Dear Michael

In experiments done with Tsotso stoves in 1999 I encountered the same 
problem of smouldering coconut husks.  They are 'burning' but not with a 
flame.  The attached picture shows the Tsotso boiling a cast iron pot of 
water with limited smoke.

The solution I found at the time that made an impact (i.e. created a flame) 
was to get the primary air preheated to the point where the addition of the 
smouldering heat was sufficient to maintain a flame.  I was wondering it 
your TLUD stove might be able to burn the smoke.  It might be quite damp 
smoke which is a huge drawback.

I also found that the burn rate was also important because it raises the 
fuel temperature more rapidly.  You can get the burn rate up by increasing 
the draft with a chimney, increasing the internal stove height (internal 
chimney), blowing on it (as with a fan), or mixing other things into the 
fuel (like oily nuts).

In Mozambique coconut husks are widely available as a free fuel but people 
don't use it much because it is SO smokey.  The fuel can cook large pots but 
it takes ages. The main reason is of course that there is almost no flame 
and most of the fuel goes off as dense smoke.

A problem I did not solve was to make a sample stove large enough to make a 
flame for long enough so that the refuelling interval was reasonable.  All 
the wood stoves I had including the Tsotso did not hold enough volume of 
husk to burn with a flame for more than a minute.  It hardly got going 
before I had to toss in more cold fuel.

If I refuelled it with small chopped pieces of husk, it would smoulder while 
heating up the fuel.  At some point the fuel was hot enough to get the 
preheated air up to temperature at which time a flame would spontaneously 
emerge, and then it would pretty cleanly burn all the remaining husk in 
about 40 seconds.  This gave a 2 or 3 minute refuelling interval which I 
figured was hopelessly short.

The solution seems to be to get enough fuel into the chamber of something 
like a Tsotso or Vesto so the preheat will reach the needed temperature. 
Both are all metal stoves.  Other options are too expensive as far as I can 
see.

You will need something like a 3 kg load I think.  It will probably have to 
be chopped up with a bush knife.  The chopping increases the fibre area 
available to the flame.

The softest part on the inside of the husk is the worst to deal with and you 
might tear it out and chuck it away.  Using the outermost parts only, made 
quite a good fire.  There seems to be a lot of resin in the outer part of 
the husk.

I am optimistic that your TLUD will be able to burn at least parts of the 
husk well.

Regards
Crispin