[Stoves] In praise of kerosene

Crispin Pemberton-Pigott crispinpigott at gmail.com
Sun May 12 17:50:57 CDT 2013


Dear Friends

 

For anyone having trouble top lighting any small fuel particles I can attest
to the following:

 

Place the fuel in the usual manner into the chamber and create a conical
depression in the very centre. If you want to use kerosene, either soak it
into small pieces of wood, or place (pour) the two or so capfuls you will
need almost entirely into the centre of the conical depression, making sure
that most of it soaks into the middle and dribbles down the centre. It takes
time to evaporate and places the flame in the low centre (which is idea).
If using the soaked wood (baby finger sized) put it mostly in the centre of
the depression as well.

 

Ignite it at the centre point. The flames will be reasonably restricted to
the centre. Because of the conical shape of the fuel pile, the flames in the
centre will tend to light the whole surface of the fuel much better than if
it has a flame rising away from a flat surface.

 

For the liquid fuel (usually paraffin but it could be wax) the concentration
in the centre means that a flame accelerated by the easily burned fuel is
always in a position to do the most heating. Having a huge rapid fire rise
from the whole surface does not do nearly as good a job as having a
continuous fire at the bottom of a conical depression heating its sides.

 

Further - if you have secondary air control, close it before starting the
fire so as much air as possible is drawn through the fuel bed during the
critical ignition period. Fire follows air. If the air is from below, the
fire will develop 'into the fuel bed' much more easily than if there is heat
applied from above and air from the side. This is critical to getting a fire
started with a minimum of time and flaming agent.

 

If you have controllable primary air, you should therefore keep it open
fully during the ignition phase. Once the fire is definitely going well,
close the primary air and open the secondary. It should jump into the
pyrolysing mode and burn the available gases. 

 

The power level is of course set by control of the primary air. Any stove
that is going to perform will should be capable of turning off the primary
air completely at will. In some cases the secondary air does not need to be
controlled at all except in the very beginning.

 

The recently developed Anglo Supra Nova (ASN) uses a lighting cone that
allows for top-lighting the charcoal and uses the cone to bypass (block,
actually) the secondary air ports. This forces all air to come through the
fuel bed, resulting in a TLUD ignition during the early stages of the fire.
The smoke is thus negligible. Primary air is fully open during ignition.

 

The removal of the cone after perhaps 5 minutes simultaneously opens the
airflow through the secondary air holes and immediately reduces the primary
air draw. For this reason (draft power is split between primary and
secondary) it is difficult to light an ASN without a cone (well, more
difficult in that it takes longer).

 

I have just received a couple of reports from Laos where the ASN has been
copied by SNV with, apparently, so much success they are rolling it out over
a wider area. I expect to hear something from GERES in the near future about
that as well. The technologies were both demonstrated to small audiences at
the GERES lab in Phnom Penh during the GACC conference in March. 

 

The stove technology was developed by the WB-CSI programme working at YDD
(Yayasan Dian Desa) in Yogyakarta in Oct-Dec 2012 and test marketed in early
2013. The lighting cone was developed with Peter Coughlin in Maputo and New
Dawn Engineering. It is used in its current format/profile to light the POCA
stove. They are now produced near Borobadur and in Yogyakarta.

 

The lighting cone has been tested successfully on several completely
different types of stoves including with damp wood where it dramatically
lower smoke emissions into the kitchen area on Sumba Island, Indonesia. It
can be used on any TLUD as a draft-inducer and I recommend everyone give it
a try. To be most successful, the outside diameter of the cone's bottom
should be slightly smaller than the inside diameter of the pyrolysation
chamber, and should extend down far enough to pass (bypass/block) the
secondary air entrances. Again, the reason for doing this is to pull all air
in the very beginning upwards through the fuel bed. This causes the fire to
develop rapidly downwards producing the essential pyrolysis zone much faster
than is possible by leaving it on its own. 

 

As this is a lighting technique and a 'draft booster' is it not clear how to
assess this as part of a stove function. I suggest that the written
instructions that come with a stove include references to the conical
depression, the placement of the ignition materials and the lighting cone so
testers will use them. It is a significant element of a clean, fast and hot
start to a TLUD.

 

In the case of TLUD stoves with chimneys, it is usually not necessary to
provide a cone, only to close secondary and open primary air ports during
the first few minutes. For all space heating stoves that have a chimney, the
placing of a heat exchanger after the cooking area, usually a box-like
structure tacked on the side of the combustion area, should have an open
bypass (that cannot be closed) to assist the development of draft early in
the fire. A suggested dimension for such a bypass is 40mm to 50mm square.
Once the fire develops, this 'leak' is not significant and ensures the
chimney is work well at all scales of firepower. As the gas volume
increases, it simply pushes into the heat exchanger. The GTZ 7 series stove
uses this approach and is one of the reasons for its rapid and clean
lighting cycle (about 10-12 minutes long for 8 kW).  Complete drawings of
that stove are available in the Library at New Dawn Engineering .com.  

 

The heat exchanger can be made slightly larger to compensate for this heat
'bleed' into the chimney resulting in the same target efficiency (say,
80-85%) but with a stable chimney draw, absent a fan. The function of this
design detail is to produce the same effect as having a lighting cone. 

 

Attached: Lighting an Anglo Supra Nova (which has preheated secondary air
and fully controllable primary air) using only wood and a lighting cone. The
cone must not be placed immediately on the wood fire - let it get going a
little then ease the cone onto it to ensure the draft does not blow out the
fire. During the ignition sequence, the emissions look like the third photo
which really does have a roaring TLUD fire inside it!

 

Regards

Crispin

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