[Stoves] About "inverted flames" ......was Re: Trials on TLUD gas burners

Mon May 5 11:32:53 CDT 2014

Dear Paul 

At some point Alexis changed from or was it to a premixed flame. A premixed
flame is like what you get from a standard gas stove which entrains air in
the gas in the long tube leading to the round burner. 

If the flame is premixed it is shorter.

You might write to Alexis to ask what the present configuration is. I know
that he has too much excess air in the current models and it was caused by
the switch from one to the other - I just can't remember at this time which
it was. The burner was created for, I think, an unmixed flame and he
switched to premixed. That means the air supply for the flame should have
been reduced the amount added in the premixing, leaving the flame in a high
EA condition reducing the temperature and heat transfer efficiency.

Alexis demonstrated the new one at the Bangkok meeting for the GACC Roadmap.

Regards

Crispin

Stovers,

I have left below the previous discussion by Ron and me.   And I thank him
for his thoughtful comments.   

 But to keep things short, here is a reply to some issues raised (much
snipped and with order sometimes changed:

1.  Ron wrote: 

I think the diffusion process is substantially similar, in both normal and
"inverted" flames. 

Are there other TLUD photos around I can look at, that show the flame
appearing between secondary air holes - not over them?

Inverted flames are conical just like regular flames.   Looking downward at
them, the parts that are over and below the air coming in are the thinnest
and the flame can appear to be absent.   But it certainly is there.
Meanwhile, the parts of the flame on the two sides of the cone are seen as
much more yellow because of looking downward through side-wall of the cone,
which can appear to be "thicker."  AND, because the sidewall flames of two
adjacent inverted cones are close together, the flames are joined and appear
to be attached to the walls of the fuel canister.  

2.  Paul A. Wrote:  

 In the TLUD gasifiers, the secondary air holes are sufficiently close
together that the inverted flames are filling the space between the
apertures of the incoming gas (which is actually air).

I should have written ".... the incoming NON-combustible gas (which is
actually air). "      Sorry for the confusion.   The INVERTED flame is still
the mixing of two gases (air and combustible gas), but with the air in the
center of the cone.

3.  Alexis Belonio's most known stoves are with "natural flames" with the
combustible gases being injected vertically into a zone of air, with his
burners looking much like a regular burner of gas fuel.   But Alexis was
discussing with me the inverted flame situation, so my comment was correct
when I wrote: 

And also, Alexis Belonio was advocating in January 2014 at the Aprovecho
Open House about some form of spreading the gases that need to reach the
secondary air that is coming in from the sides.  

Paul

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

On 5/3/2014 2:34 PM, Ronal W. Larson wrote:

***** change of topic ***********

I comment on Ron's statement: 

By looking closely, counterintuitively, the flames seem attached  NOT over
the gas apertures, but rather between them.  I think this is true in all
cases but can't see the case C "attachment" points.  Except in private
dialogs with Paul O, I have not seen this stated before in print  - and
don't know if it should be encouraged or discouraged.  

I think this has been considerably discussed or at least observed.  

[RWL:  If anyone can provide a link, that would be much appreciated.  Paul
Olivier and I never found a write-up - and it still baffles me.  Are there
other TLUD photos around I can look at, that show the flame appearing
between secondary air holes - not over them?

It relates to the phenomenon of the "inverted flame" in which the air enters
a zone of combustible gases instead of the combustible gases entering a zone
of air (which is the case of common gas burners on stoves.  

[RWL:  Well,  I think there is another explanation.  Paul Olivier has his
gas flamelets enter into air - not the "inverted flame", which I agree is or
could be substantially different.  But the Olivier/Belonio flamelets (very
short - not the typical long flames of most TLUDs) look remarkably similar
to small match or candle flames.  I think the diffusion process is
substantially similar, in both normal and "inverted" flames.  I think the
results obtained by Jim Jetter showing low particulates and CO with many
TLUD tests indicate the regular and inverted flames can't be widely
different.  The emissions are arguably superior with TLUDs - and (maybe)
independent of whether these flames seem to originate from over or between
holes.

In the TLUD gasifiers, the secondary air holes are sufficiently close
together that the inverted flames are filling the space between the
apertures of the incoming gas (which is actually air).

[RWL:  As noted above, I mostly operated with a continuous circumferential
narrow slit - and never saw this - which is why I used "counterintuitively"
Has anyone ever seen this with a natural gas multi-hole burner?  My
discussions with Paul Olivier centered on the importance of radiation -
possibly coupled with the fact that pyrolysis gases have a chemistry (not
try for methane) which gives you a smaller number of reaction particles at
the end than going in.  Makes for a helpful pressure difference.  (This
holds for whether there is gas entering air or air entering gas.)

Re the last clause ("which is actually air") needs more discussion.  There
has to be some gas there in order to have a flame.  If there were still
eight input ports, but appreciably smaller, would we see the same thing?
Does it have to do with a big air speed through the input ports?

I think there is a doctoral thesis lurking in here somewhere.   There may be
some optimum of hole diameters, spacings, shapes, separations, etc - to get
the best flames (better "flamelets").

Ron

Paul A.

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

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