[Stoves] Jatropha fruit as fuel?

[Crispin Pemberton-Pigott]

Dear Bjarne

>You can find more information on our stove on this link: www.treetanz.com
<http://www.treetanz.com/> 

The pellet burning stove is exactly the type of device that would benefit
from a few of the lessons learned during the development of the Vesto and
now the Anglo SupraNova. I encourage you to follow the development as it
progresses. Cecil just engaged the GERES people in Phnom Penh and we like
their LS (?) stove as a base.

The Anglo (Angloh) Supra is used quite widely in the sub-continent and has
the right layout for easy improvement.

I include one picture only here of the SupraNova - unfired clay in this
photo:



Which shows the basic concept. The Secondary air is provided to the gases
just above the fuel and there is sufficient space between the fuel and the
pot to allow the flame to (mostly) complete burning. Flames should (ideally)
never touch a pot. Although the stove is burning charcoal, it can easily
burn biomass pellets.

Looking at the stove on your website, there are easily added features that
will increase the combustion efficiency:

Bring the air into the combustion region immediately above the fuel,
horizontally if possible (not on an upward angle). This you can do by
cutting slots in the top wall of the fuel chamber and closing the secondary
airway at the top, forcing the air inwards. You could instead leave a
ring-gap instead of slots at the top of the chamber wall. The air gap should
be about 4 to 5mm high between the top of the chamber wall and the ring.
Radius the outside edge of the chamber wall but not the inside one. Leave it
sharp and flat. This is the approach used in the POCA and a couple of other
stoves.

Raise the pot but not by increasing the pot rest height, raise the whole
outer shell but not the inner chamber. The pot rest should be no more than
8mm high.

Use the primary air holes to control the power you want and then adjust the
secondary air gap to give about 100% excess air when running at full power.
That is an O2 level in the exiting gases of 10 to 11%. It should not be less
than 7% at any time.

In the photo above, the holes are too large. If you go with the 'holes'
approach there is a balance to be achieved between the number and the area
of each. The diameter of the chamber is involved.

I am interested to hear if you try these modifications. You may notice a
hotter burning centre region with more radiation that before, especially
early in the burn. The lighting cone will of course make ignition rapid (and
much less initial smoke).

Regards

Crispin

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