[Stoves] Down with Fantasy-draft stoves

[alex english]

Andrew,
If you are curious you can 'freeze' theTLUD process at any point by setting
the a TLUD in a pan of water that shuts off the air and wicks water into
the raw pellets in the bottom of the fuel chamber. They will swell and wick
all the way up to the Migrating Pyrolysis Front . The Torrefied layer and
the char above will not swell. A careful excavation of the fuel will reveal
all. When I did  this with the 18 inch diameter chamber I found a
horizontal layer of an inch, or a bit  less, of pellets in transition from
raw pellet to torrified pellet to charred pellet.  Misting the outside of
the stove will can also give clear impression of a planar descent of the
MPF.

With very dry fuel like wood  pellet very little primary air is required.
That primary air  can be introduced above the fuel with the secondary air
and drop down and spread out below the
pyrolysis front.  If introduced tangentially the cooler fresh air
centrifuges to the outside edge of a round chamber and the flame tornados
up the middle. A layer of fresh air one millimeter thick descending around
the edge of a fuel chamber would be enough. Not a lot of control but this
resembles what many people have used this sort in other contexts. With
fussy fuel quality and placement it behaves in the steady top down way that
a TLUD does with a little extra char burning.

Alex



On Wed, Mar 28, 2018 at 1:58 PM, Andrew Heggie <aj.heggie at gmail.com> wrote:

> On 27 March 2018 at 23:25, alex english <aenglish444 at gmail.com> wrote:
> > Andrew,
> > Setting aside the solid fuel variables, I conceive of the gasses self
> > stratifying with what ever their temperature/density properties dictate.
> > With wide fuel chambers and low velocities/momentum you might see that
> the
> > coolest of the hot gasses, which are the second most dense gasses in the
> > chamber, will spread out sideways as a cap over the fresh un-reacted air
> > that is laying/rising under the MPF.  Again, I see the cool fresh air as
> > being pulled down by gravity (even as gravity is forcing more into the
> > chamber) as opposed to being pulled up even though it is in fact rising
> to
> > replace its own transformation in to new less dense compounds with in the
> > MPF.
> >
> > There are perhaps more than a few additional variables  associated with
> the
> > chamber and burner configuration that I am not considering.
> >
> > Does this description answer your question, or make any sense to you?
>
> Yes the description makes sense  but in the absence of being able to
> probe a wide bed for temperature I don't know. I had conjectured that
> the middle would remain hotter, as the outer lost heat to the walls
> and on a wide bed the middle would start moving downward faster. Then
> it might expand out sideways and the outer parts might act as normal
> bottom lit updraught fires.
>
> The trouble with me was impatience as I would need over a season to
> dry my material to below 15% (the equilibrium moisture content in
> winter here in UK}. So I dried my small scale experiments in the oven
> but large scale experiments were with material tht was probably too
> wet. I had a brief period with our prototype small scale dryer but
> didn't make the best of it at the time and now don't have the
> facility.
>
> Also with the bigger material (I was after making lumpwood charcoal
> rather than biochar in those days before we heard about terra preta)
> there was danger of burning debris slipping down between the lumps. I
> saw this with my early burns when I arranged the fuel sticks
> vertically, if a burning particle fell to the bottom it kindled a
> simple updraught fire which inevitably smoked badly.
>
> Andrew
>
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