Juntos Stove test

["Crispin" <crispin@newdawn.sz>]

Dear Friends and Stovers Alike (are stovers alike?)

I have just had an intense visit from Paul Anderson who drove in from Maputo
this morning.  He brought two stoves and we have fun smoking ourselves out
and playing with fire.

Without saying too much about the internal constructions, I can say that
Paul has taken up the suggestion to try coconut husks as a fuel and that
they do indeed burn pretty cleanly when you get enough of them in a grate.
There is only one productive coconut palm in Swaziland but just over the
Lubombo Mountain range there are PLENTY.  The husks are a completely wasted
fuel that shows promise.

The Juntos stove is a gassifying charcoal producing stove.  He brought a
complete burner unit which I fixed to a slide-in plate for his custom-made
research-oriented Baking Stove.  This is essentially the same unit that we
have shown on the website www.newdawn-engineering.com with collapsing
features.  The stove allows Paul to slide in different burners 'on the fly'
and also to recharge the fuel container.

I had a chance to see Tom Reed's Turbo stove close up and ran the fan,
though I didn't need to light it.  It is clear how it works.  It is a very
neat little package.  I think it would be good mass produced and would
probably cost less than $10 to make in Swaziland.

Paul's slide-in gassifier unit top lights and burns down to charcoal.
During that process there are the usual flames from the top and preheated
secondary air provided, a-la-Basintuthu flow pattern.  It works well and has
I would guess about 3 kw output.  The primary air control is quite good -
nearly absolute.  We didn't have time to really check out what power range
it can change from and to, but it clearly makes a different when the primary
air is opened or closed.

The coconut test went well with the stove having preheated primary and
secondary air.and LOTS of space for fuel.

One of the things the tests today did for me was to convince me again that I
am not going for charcoal producing stoves.  There is simply no reason to do
so - or none that I can find.  The amount left at the bottom is tiny.

Someone asked my a few months ago if I had ever top lit the Basintuthu Stove
and I replied, "No".  So today l put a standard Basintuthu grate into the
baking stove, filled it 1/2 way and Paul put some of his starter mix on top.
It was lit  and we watched.

There was a significant difference in the way it burned down to the bottom
comparesd with the the Juntos.  First there was the usual gassifying/flame
that you find in a top lit stove.  It was very clean burning and basically
had no smoke whatsoever at any time, right through to the end.  The fuel
(wood) burned down to a little white ash without any problem.  It didn't
smoke at any time.

There was a strong wind gusting today and many times the flame on the
gassifying stoves and burners had to be re-lit.  This is very inconvenient.
Part of the problem was that we kept looking into the stove to see and take
pics, but even when it was closed up there were still times when the flame,
dancing as it does part way up the combustion chamber, simply went out, even
at high power.

Interestingly, the top lit charge in the regular grate that comes with the
stove did not do this flaming out.  Once embers started dropping into the
fuel load, there was enough 'real' fire in the top end of the fuel to
prevent the flame going out, even though it was ostensibly working in a
gassifying mode.  The reason for this is that there are holes all the way up
the side of the fire grate/container.  There is primary and secondary
combustion at all fuel levels.  As the fuel level dropped, so did the
combustion.  When everything was turned to charcoal, the fire simply
switched over seamlessly to a charcoal burning mode which continued until it
went out.

So, I am convinced that if you want a relatively low heat from the standard
stove, you can top light it and avoid the little bit of initial smoke that
emerges when the fuel is getting heated up.  It requires a starter mix to
get it going, and it does not have the capacity to be fired up quickly.

Bottom lighting in the same grate provides a little smoke initially until
the secondary hot air kicks in (30 to 90 seconds) and gives a lot more power
initially which is required to heat up the food and pot.  This is a
significant point.  Stoves don't just burn for our entertainment - they have
to work for a living.  We need a high heat for about 20 minutes and then a
low heat for 45 to 120 minutes.  The present arrangement seems to provide
that facility.

A subjective comparison of the Juntos and Basintuthu burners in the same
baking stove was made.  It showed me that the gassifying stove is not all
that smoke-free because at the end of the burn, there is actually a lot of
smoke.  They are very sensitive to drafts and wind.  An open flame must be
used in order to relight a gassifying stove.  When you see smoke pouring
out, it is not immediately clear whether the fire has gone out or the fuel
has charcoaled completely.  There is nearly no hope of burning the charcoal
as the air supply is so necessarily limited.

I learned that the Basintuthu grate can be top lit and is very clean from
beginning to end, but this process limits the initial power output and
requires 'starter' fuel.  When all the fuel is charcoaled, it continues to
burn without any intervention.

Bottom lighting creates some smoke to begin with and more each time fuel is
added (until it heats up the surface).  It has a power output profile that
matches the cooking requirements and requires no starter fuel other than
paper or twigs.  The fire is very stable in a windy environment because it
self-lights immediately because the flaming stage is next to the coals.

The fact there was a chimney on the stove seemed to help both burners.

Conclusion:  I still can't find a reason to build a gassifying stove, open
as I am to the general idea.  Tom's creation is very compact but needs a
fan.  Perhaps a 'wick' is required to control heat, air movement, and flame
position in an unpowered gassifying stove.

Regards
Crispin


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