[Stoves] TLUD pellets stove with a venturi burner.

Roberto Poehlmann roberto.poehlmann at gmail.com
Thu Oct 8 15:59:59 MDT 2015

Hi Paul, comments below

"Roberto and Kirk and all,

Sorry for addressing a previous message to Kirk instead of to you. So now
my congratulations go to you for some very nice work!!!
RP> thanks and no problem!

"I like to see the whole configuration, as you have shown.   That is very
important, and some results are only evident when several components are
functioning together.

At the same time I tend to divide the configuration into components to see
them separately.   Please correct me if I do not have them well
understood.   Some components are:

1.  You have a concentrator disk/ring/top.   What is different is that
you do NOT have any secondary air entering under the concentrator.
Interesting.   So the gas flow is concentrated, but without any (or
without much) flaming of pyrolytic gases.    As it passes through the
constriction and enters more open space, that is a form of the Venturi
effect.   Improvements using cones or other shapes are possible.
RP> Correct. The idea of the tube was taken looking small gasification
stoves. Some have a very nice blue flame. I only maintain the burner
diameter, and put a bigger combustion chamber below.
The idea of the cone come looking the expansion effect on some burners and
venturi devices.

I have more ideas to apply and test. For example, i tried with additional
secondary air holes at the top of the combustion chambers, in th perimeter

"2. You have secondary air entering laterally above the concentrator,
and you are getting a good flame."

RP> Yes. I found that the two rows of holes are optimal for this diameter
and size tube.

"3.  When I see blue flames, I immediately suspect considerable
char-gasification (without pyrolysis).   Please confirm that you have raw
biomass being pyrolyzed while you have the blue flame."

RP> There are no considerable char-gasification. The gases are released
because the pyrolysis of pellets. At low power you can have a good bluish

When the pyrolysis stage ends and start the char-gasification stage, the
color of the flame turn to bluish-heavenly, and the flames only start at
the tube level. In this stage, there are no flames starting at the
secondary holes located in the cone. I put 2 new photos of this flame at
the char-gasification stage. I don't know why there are no flames starting
at the cone level.

"4.  Chimney:   If the chimney is BEFORE (that is, usually below) the
pot, I like to call that a riser or an internal chimney, to distinguish
it from a commonly called chimney that is drafting AFTER the pot."

RP> It is an internal chimney, before the pot. If you put an internal
chimney after the cone an before the pot, you can increase the power
without a tall flame. The pot or kettle have no soot after one cooking

"5.  In either case, increasing the chimney will increase the natural
draft, which causes negative pressure (sucking) to PULL the gases along
(usually upward).   One force of pulling that is impacting two
"pullable" elements:  the primary air (that impacts the creation of the
combustible gases) and the secondary air (that impacts the combustion of
those gases).

6. How that one pull is divided between the two entries of air is a

critical issue in TLUD stoves (and other stoves also).   If BOTH primary
and secondary air are basically unrestricted (we know there are channels
and holes and fuel blocking, etc, but basically unrestricted), the
system tries to reach an equilibrium.   But if it pulls more on primary,
it will make more gases and those gases will need more oxygen (more
secondary air) that might need to be from the surrounding air, such as
when a tall tongue of flame needs more air than what can come in through
the stoves manufactured secondary air holes/slots/etc.

7.  So that is why it is so important to have a way to control
(restrict) the primary air.   That is, when a tall chimney is sucking
strongly, most of that sucking will be available and used to bring in
secondary air through the intended secondary air entry holes.   Strong
secondary air entry will cause the flame to be LOWER, which is good
because of better mixing and so that the pot can be closer to much more
of the flame (and not suspended up high above a tall tongue of flame
that can cause soot deposits)."

RP> Agree. Using a chimney, and with independent primary and secondary
controls, you can optimize the flame and the power of the stove. I
found that a good sealing at the primary air control is very critical
issue. Without a good sealing, i cannot obtain a good flame.

"I suspect that many readers already knew what is written above. (and
some that did not know it still do not know it because they do not read
such long messages..:-) ..).   Sorry, I got carried away."

Roberto Poehlmann
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