[Stoves] pre-mix of wood-smoke with air? and how?

[Boll, Martin Dr.]

Dear Paul,
Excuse me for answering late. I had a problem in my computer. It ran so slow
that I thought a virus was the problem, but - seen after solving it, it was
a self-made cable-problem. As far as I can understand/(better)guess, I made
a re-entry of information and I succeeded by that, to slow the
computing-speed down at least to 1/100 or slower! -I hope, by telling that
you will never make this problem in your system.-

To answer to the different points of your posting, I need once more a lot of
words. 
I want to draw your attention to the fact, I realized to be important to
remind me as well, that there are two "nozzles" in a propane/butane gas
burners, and even in the burners which are connected to "community"
gas-distribution, which have low-pressure.
The first nozzle is inside an air-sucking-tube, which makes a pre-mixture.
The second nozzle(or nozzles) are the circle of burner-holes on top.
-Which are so small, not to draw back the flame!-
The premixed gas/air mixture is able make a draw-back of the flame to the
first injector-nozzle. This makes a roaring noise, -you certainly know-,
with the consequence, if one hears it, the gas-feed must be turned off, for
not to destroy the burner by heat.
So it is not a question of real _high_ pressure to be able to make those two
steps one after the other. 
The camping burners worked in former days with a gas-pressure of 50millibar,
but the modern burners here in Germany work on 30millibar.

The other main-point weather such a two-step mixture (1.by injection-pump
2.by jet-turbulence in the at least burning flame.)is necessary or not will
depend a lot of the fuel.
When the fuel is very high caloric, there must be more air to burn, and I
guess in my simple mind, that this can be a reason to make these two steps.
As Alexis Belonios Woodgas-burner does not have such two-stage-mixing, I
think it is possibly the reason of less need of air per volume woodgas in
comparison with propane/butane.
When you wrote, that the pressure of the wood-gas-stream of that stove is
not high -and so the turbulence could be low-(I don't know the number) then
my guessing could be true.

The concentration-plate of your T-LUD: 
Did you think to set two, three or four of them in row, and give the air,
-coming from the side- the chance to enter in each space between the
concentration-plated and stream to the centre?

A time ago I thought a step further:
To set tubes with holes between these concentration-plates, in order to suck
air to the centre, because of the higher smoke-speed in the tubes, which
makes (consequently) a lower pressure. 
But at least I omitted this idea because of the lack of simplicity, which I
guess to reach in another way. But that would lead to a different
stove-concept and other discussion.
Whatever gas and its however burner, I think a re-ignition
device/construction in this will be helpful, if not at least necessary.

My experiments with out-streaming woodgas out of a 2 to3mm hole and
self-blow-out are not actually. It was just in my mind to give an example of
the difficulties I suspect to come.
For further experiments of woodgas-burning I think it will be helpful to
adapt those old-fashioned gas-burners to woodgas-habits (actual missing the
right word!!)
That is, what I wanted to know first. And out of that I wanted to derive, if
there is a good possibility for good burning by natural draft or better by
forced air.

Martin



> -----Ursprüngliche Nachricht-----
> Von: Paul S. Anderson [mailto:psanders at ilstu.edu]
> Gesendet: Dienstag, 28. August 2007 04:51
> An: Discussion of biomass cooking stoves; Boll,Martin Dr.
> Cc: stoves at listserv.repp.org
> Betreff: Re: [Stoves] pre-mix of wood-smoke with air? and how?
> 
> Dear Martin,
> 
> Your message was long, yes.  But with some relevant points.
> 
> Quoting "Boll, Martin Dr." <boll.bn at t-online.de>:
> >
> > In fact I saw simple woodgas, (without air) streaming out of a hole of a
> can
> > approx 2 or 3mm diameter, that I could not ignite, because of blowing
> out
> > the igniting flame. Therefore I think there had to be used a
> "Prallplatte"
> > (=baffle?) to have somewhere inbetween the nozzle and the baffle the
> right
> > speed to form a stable flame or/and to re-ignite. (
> 
> I suspect that this was with a forced-air TLUD.  (Natural draft does not
> get
> such movement, at least not for very long or unless there is some
> extra-special
> chimney).
> 
> You are raising a good point.
> 
> I learned from Tom Reed (and others) about the need to constrict the
> flow of the
> gases so that there was sufficient speed and therefore more turbulance.
> But I
> only did it with a natural draft TLUD, the Champion Stove that has a
> "concentrator disk" with a 3-inch (7.5 cm) hole in the middle.  BUT this
> is at
> or above the entry of the secondary air that comes in under that disk, so
> in
> effect that stove has some "early mixing".  I believe the flame is
> actually
> below the hole when the gas volume is low, but could be slightly above
> the hole
> when the gas volume is high.  I never tried to put a short tube/cylinder
> vertically on top of the hole.  Such a cylinder might confine the mix of
> air
> and gases enough to get some of the mixing that you are discussing, that
> is,
> before the actual location of the flame.  With hindsight now, a 2 or 3
> cm mixer
> (or "flame-delay") might have a good impact.
> 
> > Isn't the premixing by butane-burners the reason for clean burning?
> (Snip/edit)
> > ...propane/butane ... has to be (??) pre-mixed to burn
> > without soot by burning in a low pressure-jet/nozzles?
> 
> I have no experience nor studies about this, but I became aware of it a
> week ago
> when I cannibalized a discarded natural-gas stove for pot supports, etc.
> I
> noticed the pre-mixer and I am thinking about it concerning my Lily
> alcohol
> burner.
> 
> > As far as I have seen Alexis Belonios pictures, the burning-gasses are
> moved
> > with much more pressure. I think/guess/feel the pressure made by a fan
> > produces a comparable pressure that makes the jets of a propane/butane
> > camping-stove-burner. But take this with the famous corn of salt: If the
> > flame-speed is far less, the jet has to be slower. Possibly is the lower
> > caloric-worth of woodgas helpful to burn the jet with lower pressure/mix
> > completely.
> 
> I believe that Belonio does NOT have much pressure, certainly not anything
> similar to the pressure of propane/butane tanks.  Those gases are under
> much
> higher pressure (I think) and the gases are released via very small
> openings
> and can cause entrainment of the air to enter and be mixed.  That is not
> the
> case with the pyro-gases.
> 
> However, you have observed "woodgas, (without air) streaming out of a
> hole of a
> can > approx 2 or 3mm diameter, that I could not ignite, because of
> blowing out
> > the igniting flame.
> THAT is good.  But I feel sure that forced primary air is needed.  That
> stream
> of gases should be your starting point.
> 
> First, simply place a metal mesh (perhaps 1 mm openings) over the
> streaming
> gases and then try to ignite.  The mesh causes turbulance in the flow AND
> can
> be a "flame holder" if hot enough.
> 
> Second.  How much can you entrain (confine) to the mixing tube WITH some
> secondary air, and still have NO flame in the tube?  But you also want to
> be
> able to ignite (with control) that mix when it leaves the mixing tube.
> IF that
> gives you a better (cleaner, more controllable) secondary combustion, then
> you
> have a very important result.  We can solve the easier problems later
> about
> keeping that mixing tube hot enough to prevent condensation.
> 
> Sounds interesting.  You have caused me to re-think my earlier comments.
> 
> Said slightly differently, those of us working on the gasifier stoves are
> now
> able to make the gases reasonably well.  Quite possibly the future
> progress
> could be more focused on how to combust those gases better than we do at
> present.
> 
> Paul
>