[Stoves] ***SPAM*** Fwd: [Biochar] Clean burning of wood gas

[Harris, Kirk]

All,

There was a recent discussion on the biochar list about turbulence in 
the mixing of wood gas and air for burning.  Ron Larson stated that this 
also belongs on the stoves discussion list.  The below and the 
attachment describe my disagreements with turbulence for mixing in a 
TLUD and describes my hypothesis for a better mixing system.  It is the 
the same system used in the 3 hour TLUD stove I described in an earlier 
contribution.

I had a very difficult time when I started working on the Wonderwerk 
TLUD test stoves ~5 years ago.  I realized how little I knew about the 
processes going on inside the TLUD that make it work.  I wondered about 
pressures, temperatures, velocities, and mixing and tried to learn what 
I could.  No papers that I found covered what I felt I needed to improve 
the stove designs.  I began to look into what makes a stove do what it 
does.  First I attempted to figure out why the flame goes up through the 
stove.  This landed me on buoyancy.  My high school physics taught me 
that buoyancy had to do with a boat in water.  That had to be extended 
to understand how buoyancy works in a TLUD, or any wood or gas stove.  I 
developed theories which changed and improved over time, and are still 
changing.  Buoyancy lowers the pressure inside the stove to below 
atmospheric air pressure.  That is what brings the primary and secondary 
air into the stove, the air follows the pressure gradient from higher 
pressure outside to lower pressure inside.  Once I accepted that 
buoyancy was moving the gasses I began realizing that the moving gasses 
had an effect on the pressure variations in the stove through such 
things as the Venturi effect, back pressure up stream of a restriction 
in the flow path, and directional impact pressure.  Then ideas began 
presenting themselves as to how these pressure variations could be used 
to improve mixing.  This lead me to notice a mixing technique in the 
Peco Pe and Champion TLUDs.  At the upper edge of the fuel chamber the 
wood gas meets the secondary air.  The full _*pressure difference*_ 
between the outside atmospheric air and the lower buoyancy provided gas 
pressure inside the stove was pushing the gasses together.  Since gasses 
are permeable, they could merge, and the mixing here is excellent, 
molecule to molecule.  The flame is smooth, laminar, without turbulence, 
and yet it was a good mix.  However it looked to me that this mixing was 
not optimized since the air could not reach the gas at the center of the 
gas column.  I set about to design a burner which would optimize this 
mixing system.  That is how I arrived at a mixing system that does not 
use turbulence.  I tried a number of designs, including the Wonderwerk 
stove that was tested at Lawrence Berkley National Lab, which was quite 
clean at moderate power levels.  No design seemed to solve all the 
problems.  I wanted it to be simple and cheap to build, and to be able 
to turn the power level up without the burn getting dirty.  I was 
assisting Dean Still at Aprovecho with a different experimental design, 
and after I left to come home, Dean continued his experiments.  He found 
a way of cleaning up the flame without making the burner complex.  He 
told me about it, and I thought through it.  I realized that his design 
fit the pressure theories that I was developing.  I adapted his idea to 
the TLUD-ND stove and it seems to work.  It is simple, and the power 
level can be turned up quite high before it begins smoking.  In fact it 
can tolerate some forced primary air increasing the power level very 
high.  It can also be turned down to a stable low flame.  See the 
attachment for a description of this mixing technique.

Respectfully,

Kirk H.

On 12/27/2020 8:54 PM, Norm Baker wrote:
> Kirk;
>
> I cannot imagine how your stove does not need turbulence for complete 
> combustion.
>
> The simple fact that the flames are exiting the top indicates at least 
> some turbulence and there
> has to be turbulence just to mix the woodgas or pyrogas with oxygen.
>
> Please explain. Very interested.
>
> Norm
>
> PS How's my cat doing???
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