[Stoves] TLUD pellets stove with a venturi burner. Pictures of a cooking cycle.

Tue Oct 13 20:29:07 CDT 2015

Roberto,
I may have missed this detail, but what is the diameter or area of the fuel
chamber?
Alex

On Tue, Oct 13, 2015 at 8:31 PM, Roberto Poehlmann <
roberto.poehlmann at gmail.com> wrote:

> Dear Alex, thanks for your comments. Below some commentaries.
>
> "Roberto,
> I like what you have done. A stable blue flame is interesting. Do you
> think you are getting a bit of premix happening with you lowest secondary
> holes?
> I have two theories about the colour. One is a combination of premix and
> excess air. The other is that at low turn down, low superficial velocities,
> you get peak bed temperatures down around 500C or even lower at the sides
> of the chamber or maybe even inside the pellet. I think there might be a
> different mix of gasses at these temperatures that make it easier to burn
> without forming soot that turns the flame yellow/orange. Perhaps a lower
> C/H ratio.
> When I add a logs to a bed of coals in my stove, with the primary air
> shut, I see dancing blue flames for quite a while before they turn yellow."
>
> RP> Alex, i have tried to premix the gases before burning it, but without
> much success. With this burner, you see flames emerging from every holes,
> so, i think there is not a premix flame. At the first row of holes, the
> flames forms a plane (completly blue) with vertices starting at every 8
> holes.
>
> About excess air, maybe it is the cause of the blue flame generation, I
> don't know. But, to contradict that, at the first rows of holes, you can
> see blue flames starting at every holes, where there is excess of smoke.
> Maybe, when the flame disappears at the top of the burner, there is an
> exccess air. I cannot determine if i had or not excess air. I only can see
> the flames, smell the gases and put the eyes at the exhaust gases to
> determine if i have or not a good flame.
>
> My next step, as Crispin says once, is to measure the exhaust gases with
> the adequate equipment, to optimize the stove.
>
> Another thing i discover, is that a certain conditions, the flame start at
> the base of the cone and not inside the tube. The reason i thing, is that
> the velocity of the "premix" gases at the tube is greater than the flame
> velocity, and when the premix gases reach the cone, velocity decreases,
> sufficiently to stabilize the flame. I see this phenomenon two or three
> times, and i have no idea how to reproduce it. Maybe is a way to have a
> premix flame.
>
> About the idea of the low superficial velocity, maybe is one of the
> reasons to produce a blue flame, i don't know (again). If you suddently
> close the primary air control at normal operation in a TLUD stove, the
> flames turns more yellow/orange, and if you open the primary air control
> again after a few of seconds, the flames turns completly blue, before it
> stabilizes again. ¿Why?
>
> "I had a choked exit on some of my TLUD burners, cone in to secondary air
> and cone out. I called them venturi burners because of the look but I
> abandoned the name because I felt it was all chimney-effect.  I'd like to
> see you have control of the secondary air on the cylinder portion.
>
> If you get a combustion test done, don't be surprised if the best result
> is with a flame with yellow tips.
>
> Nice work.
> Alex"
>
> RP> Thanks Alex. Maybe the mos important factor is the chimney effect as
> you say, and the venturi effect is not as important. What i see is that the
> cone helps to widen the flame. Without the cone, the flames transforms it
> in a tall flame, so the shape of the burner (tube and cone combination)
> helps to maintain the flames near the surface of the cone (venturi effect?,
> sudden expansion effect?).
>
> Here is a link to a series of photos and videos of a cooking cycle
> executed yesterday. Every picture have the time printed in it, to see the
> evolution of the cycle and flames behavior.
>
> https://www.dropbox.com/sh/0ltk3o6pbzanz90/AAAUWrVtNho7ITuBa3eoyR3na?dl=0
>
> I have burned 3 kg of pellet.
>
> At 13:51, i started the fire with the 2 primary air control fully open and
> the 3 secondary air controls fully close.
>
> At 13:59, i closed the primary air controls, and fully open the 3
> secondary air controls.
>
> At 14:02, i remove the chimney, to lower the gasification rates to see
> what happens.
>
> At 14:04 i put the chimney
>
> At 14 29, i remove the chimney, to lower the power or gasification rates
> again.
>
> At 15:17 i put the chimney again.
>
> At 16:02, i fully open the primary air controls, and close two of the
> secondary air controls
>
> Between 16:03 and 16:08, started the char gasification stage.
>
> At 16:26 , i close more the only open secondary air control.
>
> At 17:06, the flame extinguish
>
> At 17:07 i can ignite again the stove.
>
> At 17:13 the flame extinguish again.
>
> The char and ash left weight 230 grams.
>
> The pyrolisis stage last 2 hours and 10 minutes aprox. The gasification
> stage last 1 hour more aprox., before the first flameout.
>
> If i put a more taller chimney, maybe i can have 30 to 45 minutes more
> with flames.
>
> With this prototype, i am very satisfied with the results, and fullfill my
> requirements of an outdoors cookstove and patio heater with natural draft
> with pellets.
>
> I can see that to lower the power with a chimney, i need to have a more
> sealed primary air control. My goal is to reach the 0,5 kg/hour rates. That
> is, 6 hours with 3 kg of pellets.
>
> Greetings
>
> Roberto Poehlmann
>
> Valdivia, Chile
>
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