[Stoves] Briquette ignition in a Vesto Junior

[Rok Oblak]

Thanks Crispin, for comments and photos!

An additional comment regarding the gap around the briquette - At later
stages of burning the briquette partially shrinks and starts to burn from
the outside as well, this helps to burn faster in that stage which is
really important as briquettes give loads of CO in late stage and burn less
powerful. The gap around is a simple feature helping the briquette to burn
equally at all stages

Agree on the center hole and gaps, referring to scandinavian burning logs,
it can be dense and long! Its exactly what you're saying, that it helps to
ignite the next briquette in line. If you obsere the flame in the briquette
hole, it is visualy always present if there are 2 briquettes or more, but
sometimes it goes out if theres a single briquette; its much harder to
sustain a constant fire with only one briquette, especially if briquettes
are of bad quality

Interesting thought on lifting the pot and how the user might not find that
being a problem. Some cooks really have hands of stone and are not sensible
to heat as much as you'd think.. They have to hold the pot anyways if
mixing vigorously like for nsima, so lifting really should not e a big
deal. But maybe a more useful feature of side feed i forgot to mention is
the visual contact with fire - do you find this being a problem in some
stoves?

Rok

On Friday, August 3, 2012, Crispin Pemberton-Pigott <crispinpigott at gmail.com>
wrote:
> 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:
>
> </mail/u/0/s/?view=att&th=138eddb53711bc58&attid=0.0.1&disp=emb&zw&atsh=1>
>
>
>
> Stove body (not all internals shown)
>
> </mail/u/0/s/?view=att&th=138eddb53711bc58&attid=0.0.2&disp=emb&zw&atsh=1>
>
>
>
> A user of a Vesto Junior
>
>
>
> </mail/u/0/s/?view=att&th=138eddb53711bc58&attid=0.0.3&disp=emb&zw&atsh=1>
>
> 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
>
>

-- 
*Rok Oblak, MAA Design*

rok.stoves at gmail.com
www.holeyroket.com

Gregorciceva ulica 5
4224 Gorenja vas
Slovenia
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