[Stoves] T-LUD with central core: derived from Dung Berry Fireballs

[AJH]

On Tue, 31 Oct 2006 23:54:34 -0600, Paul S. Anderson wrote:

>1.  The core must not allow fire (via falling embers, etc) to fall to 
>the bottom
>and to cause a bottom-lit situation.

I see your intent here and for the sort of downward pyrolysis front
you are seeking to sustain this is entirely correct but I would like
to note that there is still a place for top lighting a fire that then
sustains itself in a bottom burning mode on grounds of clean starting.


>  Therefore, the core is mostly closed and
>rather small in diameter.  I envision a hollow metal tube perhaps 1 cm in
>diameter with perhaps two of 1/8th inch holes (about 3 mm) placed at 1 cm
>vertical spacing.  More holes can be added if needed.

You may well find such a part in the silencer of a small motor cycle.
Motor car silencers are generally >30mm but are perforated in this
way. Consider also making it with a woven wire mesh rolled into a tube
and held as a cylinder with metal rings, cut from tubing, at top and
bottom.
>
>2.  There is a clear passage for primary air to get to the bottom of the
>vertical hollow core.  If there is too much passage of air, the core might be
>partially closed at the top.  

We decided on much the same scenario when using our high temperature
dryer to circulate through chips and sawdust, it becomes a trade off
between how much heating you can pass through the walls of the tubing
by conduction against the cost of fan pressure to circulate it through
the whole mass. I decided that heat was cheaper than electricity for
the fans.

In the tlud device I think the tubes are only necessary to vent the
pyrolysis offgas to the secondary combustion area, the energy for
propagating the pyrolysis front is probably derived from radiation and
conduction between particles, convection is not a likely candidate as
the hot offgas is carried away from the front rapidly and replaced
with fresh air. Spacing these tubes to optimise how primary air will
diffuse through them to the pyrolysis front will be an interesting
experiment.
 
AJH