[Stoves] TLUD pellets stove with a venturi burner.

Thu Oct 8 09:02:01 CDT 2015

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!!!

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.     
(Continue)

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

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.

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.

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).

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.

************

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu
Skype: paultlud      Phone: +1-309-452-7072
Website:  www.drtlud.com

On 10/8/2015 7:00 AM, Roberto Poehlmann wrote:
> Hi Kirk,
>
> Maybe i have named the top of the combustion chamber with the wrong 
> word (concentrator ring). The combustion chamber has on top a 3 inch 
> hole, and no secondary holes inside the combustion chamber below the 
> concentrator ring.
> The 3 inch hole "concentrate" the smoke to the tube burner.
>
> When the primary air control is wide open, i can obtain a good flame 
> with a taller internal chimney to increase draft. Another way to 
> increase secondary air flow without a chimney is to add a fan.
> The experiment, with a taller chimney, also make me doubt about the 
> importance of the venturi effect versus the draft of a chimney. With a 
> normal TLUD burner (Peko Pe or Champion stove for example) you can 
> also have a short flame with a taller chimney.
>
> Another way, as you say, is to add more than one burner.
> I have made sometime ago, an experiment with 4 similar burners on top 
> of a 18 liter chamber. The problem i had, is that always a burner 
> draft "lose" vs a stronger draft of another burner. The weakest burner 
> acts like a primary air control, and i never had a "positive" draft 
> for all of the burners at the same time. If i restrict the weakest 
> burner, another burner take the place with negative draft.
>
> The solution is to put a fan at the primary air control, like Paul 
> Olivier did, or with the subdivision of the combustion chamber in 4 
> independent chambers, each with his own burner on top. All of the 4 
> independent chambers can "share" the same primary air control below.
>
> I have no equipment to test particulates or gases.  The equipment are 
> very expensive for me. I am not a stove constructor (yet). But i thing 
> the stove would have very good results. Maybe you, Julian or Crispin 
> can contruct this burner and make some measurments to test it.
> I have made some variations of the tube, with distinct sizes and holes 
> configurations, and i found this is the best configuration for now 
> (best looking flame).
>
> Thanks for the photos of the control valve. Maybe i will construct 
> something similar.
>
> Here are some photos of the same burner (tube and cone) and the same 
> beer barrel, in another similar configuration stove:
>
> https://www.dropbox.com/sh/af6b6gfihhw4psj/AAD6cuP8q4PMGTCDSMJqfXDGa?dl=0
>
> This is a video of this stove with a taller chimney:
>
> https://youtu.be/j6BfGrPsvt8
>
>
> Greetings
> Roberto Poehlmann
>
>
> "
> Roberto,
> Nice.  I would like to see test results for particulates.  It should be very clean.  It looks like it is loosely based on Crispins flame tube design with holes added in the tube where the Venturi low pressure area is.  The holes are at the bottom of the burner, so there is better draft and a good burning area above.  If I understand correctly Crispin is using the tube differently, to concentrate the heat and increase the dwell time for the flame in that hot environment.  His secondary air is all added before the flame tube.  Your design looks more compact and perhaps would be a better choice for a TLUD.
>
> There is a limit to how much gas the burner can handle.  When the foil is removed and more primary air is added the burner is overloaded with gas and a tall diffusion flame forms.  I have been trying to handle this problem by adding more mixing capability, and have had some improvment, but further work is needed.  The problem with the mixing tubes I am using is that along the edges of the combustor, the air exiting the tubes exits at an angle instead of straight out.  This holds the gasses below the burner along the edges, and adds to blowing them to the center, overloading the center of the mixer and wasting air at the edges of the combustor.  This would not be a problem with your design.  You might be able to use two or three of theses mixers side by side to gain a clean higher fire power.
>
> The concentrator ring is intended to mix the wood gas and air, and the Venturi mixer is intended to mix the wood gas and the air, so you have a duplicate mixing system.  I am not saying good or bad, just something I notice.
>
> I see Julian has expressed some doubts about the Venturi concept.  Good for him.  I would be very happy if someone with adiquate equipment and technical ability proved or disproved the TLUD Venturi concept, either way.  I perhaps will have to bite the bullet and buy a manometer with the ability to measure down to .001 inch of water column.  My rather primative home made manometer did show a slight pressure drop at the mixer, but not enough to get any measurments.  Our local college science department didn't seem to be interested.
>
> Attached are some photos of the primary control valve I am currently using very successfully.  It looks like something similar might work for you.
>
> Good work Roberto,
>
> Kirk
> "
>
>
>
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