[Stoves] Cross-Current Woodgas Burner with Air Inlet Tubes Angled 45° Downwards - YouTube Vid

[Julien Winter]

Hi folks;

I have posted another vid.

Cross-Current Woodgas Burner with Air Inlet Tubes Angled 45° Downwards

https://youtu.be/QmnUgj75TF0

This video is a brief introduction to work in progress.  The main objective
is to design woodgas burners that (1) cause good mixing of air and woodgas
over the top of the fuel bed char, or at least at the base of the gas
flame; (2) create a flat flame that retains heat, as opposed to a tall
conical flame that can cool off at its edges resulting in incomplete
combustion (e.g., of soot).

The burners in this video were designed to give horizontal space for
woodgas flame expansion so they are 1.2 to 1.3 times wider than the
circumference of the TLUD reactor.  (If they are wider, they produce smoke
at low gasification rates.)

There is an experimental series of five burners with 8, 12, 16, 20, and 24
tubes.  Only the 8 and 20 hole burners are being tested at the moment.   It
is expected that the burners with 20 and 24 tubes will be the most
efficient, and produce the lowest polluting emissions.  The reason for
including burners with fewer tubes is to document the reduction in burner
performance as tube number decreases.   If this tubular design is adopted,
it is expected that some stove-builders may want to use fewer holes,
because the burners will be easier and cheaper to make.  We need to prove
why this is a bad idea.

On the metal burner, there is a narrow deflector ring inside the riser that
functions to prevent vertical flamelets going up the riser walls.
Curiously, there can be both a horizontal and vertical flamelet originating
from a single air hole.  The vertical flamelets are cooled off by the riser
walls, and emit soot.  The deflector ring also prevents unburnt woodgas
from escaping up between air holes.   This problem increases as the space
between holes increases.   The trials in this video showed that a deflector
ring should also be fitted to the burners with tubular air holes.

The burners with conical tubes are made with cones with edges that radiate
out from the central, vertical axis of the burners when tubes are
horizontal.   The purpose of the conical shape is to reduce air friction
along the sidewalls of the tubes.  The tubes create a laminar flow of air
that is pointed inwards, and at a 45° angle downwards.  In the present
experiment, the horizontal diameter of tube at the air outlet and the space
between outlets is kept the same.  That means that as the number of air
tubes decreases, the total area for the ingress of secondary air increases.

The burners with conical tubes are made of refractory cement (Imperial
Manufacturing Group, Richibucto, NB, Canada) and perlite in a 1:2 volume
ratio.   The use of perlite is going outside of the manufacturer’s design
parameters, and I don’t yet know if this recipe is durable.  The reason for
using perlite was to reduce the weight, because the stove will be run on a
weight-scale.  A burners weigh about six kilograms.   The surfaces of the
burners were coated with refractory cement paste to create smoother
surfaces.

The burners in these videos were sized to work on larger diameter TLUDs (18
cm) burning rough fuel, so the flame structures are coarser than with small
TLUDs designed for only pellet fuels.  The present prototypes don’t preheat
the secondary air.  They should also be operated out of the wind, because
gusts will cause secondary air intake to increase on the windward side.
If burners like these are operated out in the open, the secondary air
intakes should be shielded.

Thanks to Crispin P.-P. for his advice on the “artificial pot” placed on
top of the burners’ risers to prevent downdrafting of ambient air.

Now I need to read over the exellent comments from the previous vid. and
reply.

Cheers,
Julien.


-- 
Julien Winter
Cobourg, ON, CANADA
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