[Stoves] Briquette ignition in a Vesto Junior

Fri Aug 3 13:58:44 CDT 2012

Dear Rok

Good to hear from you and thanks for providing measurements. Numbers inform.

>I've experimented with top-feed briquettes quite a bit and figured out a
few points:
- the gap around the briquette as you've also found out, needs to be there,
around 3-5mm all around, if not, there's some kind of a choking smoke coming
out at sides and the fire doesn't seem to progress well

I agree but hold that there are several ways to burn the same fuel,
including having no gap. The short version is that it has to do with what is
happening on the outside. The photos are shown looking straight down and
there is a small provision for primary air in the outside of the briquette.
The need for it is later in the fire when the charcoal is burning as the
primary/secondary air split changes when the fuel is pyrolysed. You are
correct, however, under certain conditions.

>- i think its better to have more shorter briquettes than one or two long
ones, as the gap between the briquettes provides an extra air-pocket that
seems to help the fire going 

If the centre hole is large enough (basically, exactly the right size) you
can burn a very long briquette. I think the reason for your observation is
that the hottest briquette is able to pyrolyse more completely before
developing a fire in the next in line. If the fuel is really dense they have
to be even smaller (vertically).

>.from 3-5cm to 10-12cm, but stayed with around 5-7 cm

George is on that upper range at 7.5 cm.

>- now comparing the top or side-feed, i found quite a few reasons to
proceed with the latter, side feed: 

You are using a bottom-fed updraft tipped on its side (side fed crossdraft)
and that has some advantages. The stove in question is portable even when
the fire is running and I think there are safety advantages with a fully
contained fire. 

>.when you insert a briquette from the top on an existing fire, there is a
much bigger fluctuation in fire volume,

Agreed.

> higher CO emissions and you have to lift the pot while doing it.

I always work about pot lifting. I found that the people who complain about
it the most are stove designers, not users. J They don't like it
theoretically but skilled users are able to do amazing things. I have heard
about a 2 hours burn in a Vesto without touching it. 30-45 minutes is
common. The problem is overestimated in my experience.

> The major difference is that with the top feed, the cold briquette mass is
instantly all exposed to the fire, while in side-feed the briquette burns
inside-out, starting through the hole, which gives a much steadier flame
volume and way less smoke and CO emissions, also the briquette is always
inserted where the fire is the coldest - from the side. 

That is a major difference and it depends on what the user wants. There are
many cooks who want a string flame-low flame-strong flame. It is easy to
mediate that with the number of stacked briquettes. For example you can have
the remainder of one plus a new one, or three new ones. The power is thus
controllable to a certain extent. I foresee people dropping in briquettes
made of completely different materials to get the burn they want. 

>Top feed was my first briquette stove in Malawi, with 16cm briquettes outer
diameter and cca 5cm hole. What did work much better than, was keeping the
fire going and manipulating the steady volume with few wood-sticks from
underneath, 

I remember that. It was a combination of fuel wood and briquettes. That is a
perfectly reasonable approach if both fuels are available. I believe that
one can make a stove to suit the fuel, even when it is difficult to burn the
fuel.

>.Also it was easier to persuade local people for using briquettes as it was
an easy-learning curve. 

I completely agree. George is working with people who have to buy their fuel
wood so there is a huge motivation to save. He will report shortly on the
savings. The money side of the cooking is a significant factor in adoption
of odd fuels or stoves.

>I haven't gone in this direction yet, but i'm sure that with some
air-supply regulations, it would be possible to improve the top-fed stove as
well! 

The key is to be able to burn multiple fuels. The Vesto Junior is a really
good charcoal stove which is perfect for some meals. It is being used with
wood and with briquettes, in both cases providing an economic benefit.

>I would be happy to hear about how the locals are satisfied with the stove
you're posting about and if the fire volume fluctuations is not a big
problem for them! 

George will report that.

>Would be also great if you could post some photos of the whole stove body

Here: (nothing unusual)

Combustion chamber:

Stove body (not all internals shown)

A user of a Vesto Junior

There is too much wood in the combustion chamber - that extra fuel makes it
smoke but increases power (a lot) so people do it anyway.  The fuel should
not be above the rows of secondary air entrance holes. There used to be a
standard plastic grip on the wire handle. You can just see a double top lip.
The inner part is all the innards you can see. It is sitting on that groove
and is removable.

Regards

Crispin

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