[Stoves] Fwd: Rapid mixing

Thu Sep 29 21:00:06 CDT 2016

Ronal,

The video shows the flame in the funnel at the bottom and the circle of the
6 inch pipe at the top. If they were in the same plane then the flame would
be interpreted as 3 inches wide. But they aren't. |The flame is closer to
5+ inches wide.

I won't reveal my motivations until I succeed.... other than to say they
are totally frivolous and of no particular interest to this list. Glad to
know that there is incidental interest though:)

Alex

On Thu, Sep 29, 2016 at 9:04 PM, Ronal W. Larson <rongretlarson at comcast.net>
wrote:

> Alex, cc list adding Paul Olivier (not usually on this list)
>
> 1.  Nice new test.  I am unaware of anyone else who has demonstrated
> premixing (except see below on one).  Really good to see any work along
> these lines.
>
> 2.  Some comments:
> a.  It seems the flame diameter never exceeded about 3 inches.  I think
> the flame doesn’t expand out to fill the full 6” max diameter because the
> pressure inside the flame is lower than outside.  Lower because the number
> of particles goes down with both CO and H2.  Ex:  2 H2 + O2 .>> 2 H2O  (3
> molecules goes to 2);  same for the CO equation 2 CO + O2 >> 2 CO2.
> b.  It would be nice to see more in the vertical direction.  Perhaps doing
> this with a glass cone or a set of small observational holes might give
> some more insights.  I can conceive that your flame gets smaller in
> diameter as it rises (because all flames seem to do so).
> c.   There should be some data around on flame speed for TLUD-type gases.
> This 3” flame diameter number could be a way of learning more on the gas
> constituency.  That is - why not a 2” or 4” flame when viewed from above?
> d.   There might be less than full mixing in your geometry;  putting in
> some barriers ( a few inches of mineral wool?) to vary the time (or
> geometry) for mixing distances might be interesting.  I remember reading
> once of variations in the length of Bunsen burners (which is different
> because   CH4  + 2 O2 >> CO2 + 2 H2O give equality of 3 on each side.
> As an aside:  with the LPG gases, propane (C3H8) and butane (C4H10), you
> have more particles after combustion.  It looks like you could repeat this
> pyrolysis gas experiment with these three other gases - and we might learn
> something.  (Remembering there would be temperature differences that would
> make it difficult to draw conclusions.)
> e.  Can you say a bit on the secondary air inlet.  What total area?  Any
> chance there is, or could be, a swirl?  (to give more time for
> pre-mixing).  Similar would be seeing the effect of changing the length of
> the riser, before getting to the flame.
> f.  If you had a 3” (or more) riser pipe diameter instead of 2”, would the
> flame have appeared at the secondary air holes?
> g.   Not sure what you would learn from this, but what if the 2” riser
> suddenly expanded to 4” (no cone).   My guess is that the short video would
> look about the same - about a 3” diameter flame as viewed from above.
> Another way of saying this is that the upward flowing pyrolysis gases flare
> out, and happen to be the right velocity when they are about a 3” diameter.
>  (but you are avoiding eddies with your geometry.)
> h.  This last rambling thought makes me ask whether you can now (or soon)
> change both the primary and secondary air quantities?  I think there is a
> possibility of some interesting changes.  For instance, if you don’t have
> enough secondary, then the needed combustion air will have to flow downward
> in the cone.  If you have a lot more secondary than you need (or could
> change its temperature), then maybe the 3” flame diameter would presumably
> change a little.
> i.  Same for primary air variations.  As you point out there should be a
> change of gas composition that might tell us something new.  At the present
> time, you have a fuel bed of 12” diameter.  What is the fuel-bed height,
> and can you say more on the pellet (if pellet) size?  How long to go
> through a run?  If you are saving the char - how much?
>
> 3. What led you to try this experiment?  (Were you expecting the very nice
> looking flame - and why?)
>
> 4.  Pre-mixing could be advantageous for cooking (being such a nice
> looking flame) for health reasons (assuming you are dropping the count of
> 2.5 micron particulates).  Have you tried to see what sort of “plaque”
> might be left on a cold surface above the flame?
> Another advantage for cook stoves is that you could get multiple burners
> going.  (And it should be easy with smaller pipets each burner)
>
> 5.  Paul Olivier and I talked over some TLUD experiments with pre-mixing
> several years ago  (very different geometry).  He didn’t like the results -
> so I am adding him to this message for comments.
>
> Thanks for the sharing - and (in advance) for any answer to my too-many
> questions above.  Questions on your few sentences below are all covered
> above.
>
> Ron
>
>
>
>
> On Sep 29, 2016, at 3:37 PM, alex english <aenglish444 at gmail.com> wrote:
>
>
> Crispin,
> I don't know about the chemistry in the reaction zone, except that I would
> expect more hydrocarbon "tars" to remain with the char at lower
> temperatures.
>
> I am not currently tooled for combustion gas analysis. When I was, this
> flame would test at <100ppm CO and 8~10% CO2.
>
> Secondary air was not preheated beyond incidental ambient heat from the
> stove. it would be easy to get significant controllable preheat off the hot
> edge of the funnel.
>
> Alex
>
> On Sep 29, 2016 1:01 PM, "Crispin Pemberton-Pigott" <
> crispinpigott at outlook.com> wrote:
>
> Thanks alex
>
>
>
> If you run a higher superficial velocity I would expect to see the flame
> turn more to the blue, but it is already blue. Is it possible the H and all
> what we would normally see in the ‘flaming pyrolysis’ is taking place
> inside the bed? That would be pretty hot, no so?
>
>
>
> Very interesting. Great video. What’s the CO/CO2 ratio in that condition?
>
>
>
> When the premixed air is added, what is the temperature going in? Harold
> thinks we should investigate that. I agree. I’ll ask Riaz at CAU.
>
>
>
> Crispin
>
>
>
>
>
>
>
> No, but it is produced with a pyrolysis front at a temperature (500c ish)
> at the low end of normal for a TLUDs filled with wood pellets. There are
> some unanswered ( or demonstrated) questions here. To match burn rate with
> a higher py-fr-tp I need to use a smaller fuel chamber and increase the
> superficial velocity. This will perhaps produce a different gas
> composition. We'll see...
>
> Alex
>
>
>
> On Sep 29, 2016 9:00 AM, "Crispin Pemberton-Pigott" <
> crispinpigott at outlook.com> wrote:
>
> Dear Alex
>
>
>
> is that flame produced late in the pyrolysis? ‎By that I means in a carbon
> 'evaporating' stage.
>
>
>
> Thanks
>
> Crispin
>
>
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