[Stoves] Jatropha fruit as fuel?

[Bjarne Laustsen]

Dear Crispin

The secondary air enter into the combustion through 3 rows of holes in 
the bottom part of the internal chimney in the top part of the stove. We 
have designed this internal chimney to have a height allowing the gasses 
to burn without going over the top of the stove. So the flame will not 
reach the pot if the stove is operated in the right way.

We have earlier tried to bring in the secondary air closer to the fuel 
bed, however it was not very successful. For me to see it is necessary 
to have a separation of of the fuel bed and the burning of the volume 
where the gasses are burnt if you operate gasification stove, else it 
does not work satisfactory.

The burning of the gases in the internal chimney gives heat enough to 
keep the pellets hot enough to release the gasses so that is not a problem.

A problem with this separation of the two is that in strong winds the 
flames can be blown out, if this happens the stove stops operating and a 
lot of smoke will develop. This is not a big problem here as most 
households cook in sheltered places, so we have not got complains on 
that. The stove can also get started again if a light match are dropped 
down into the internal chimney, this will get the gases to burn again.

Yours
Bjarne Laustsen



On 1/24/2013 5:04 PM, Crispin Pemberton-Pigott wrote:
> Dear Bjarne
>
> It is now clear - there are two sections of the stove - a gas making unit
> and a mixing/burning unit.
>
> I am still missing one critical piece of information: where does the
> secondary air enter the upper unit? It seems to have all the basic parts in
> place.
>
> There is a feature, not in the positive sense, that man gasifiers have which
> is to separate the gas burning from the fuel bed. There is no essential
> reason for doing this. It actually introduces two new problems that should
> not be there which are: separating the radiated heat from the underside of
> the flame from fuel bed and the addition of the problems related to the
> flame going out and not re-lighting.
>
> Thus, where you add the secondary air is critical. It can prevent both
> problems. It would be unfortunate if you were spending money and effort to
> create a problem that should not be there.
>
> I did not realise without the photos that you had a removable upper section.
> The photos helped a lot in clearing that up. If the secondary air were
> pushed into the gas at the top of the fuel containing section and the plate
> with the triangular holes were not present, what happens? If there was the
> same top round disk placed at the top if the fuel container - or better, at
> the bottom of the upper unit so it is removable - it would push the
> secondary air into the gas near enough to the fuel to help keep it hot. The
> 'disk' could have any of a number of complex shapes to promote mixing, but
> the point is that the secondary air should not be added near the top because
> it means the flames will be running against the pot spoiling the CO and PM
> burn. That is why I am asking about where (am perhaps how) the secondary air
> is introduced.
>
> The stove looks quite strong.
>
> Regards
> Crispin
>
>
> Dear Crispin
> Here is some pictures of the Jiko Bomba casification cookstove.
> The first shows the two part of the stove with pellet as fuel in the firebox
> before fire is lit.
> Second show the stove burning.
> The third the same, in the end of the gasification.
> The forth shows the charcoal stage where the pellets remains as glowing
> carbon. A pot can be put on top of the bottom part of the stove, there are
> three supports for that.
>
> Yours
> Bjarne Laustsen
>
>
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