Stovers,
This message was held in the Moderator's box, so I will resend it now.
Paul S. Anderson, PhD aka "Dr TLUD"
Email: [email protected] Skype: paultlud Phone: +1-309-452-7072
Website: www.drtlud.com
On 4/14/2013 9:49 PM, Paul Anderson wrote:
Dear Alex, Lanny, Dean and all,
We are learning things about short flames and flame color that should
have been learn years ago!!! Thank you both (and others) for getting
this information to us.
And Crispin has been telling us all along (and showing up with his
device at ETHOS etc) that a combustion analyzer is useful. We (the
generic we) need to get more serious.
And Dean wrote:
>The very hot yellow/white flames easily make black carbon.
>The less hot deeper yellow/red flames make less/no black carbon.
Notes:
1. Why isn't a combustion analyzer (as used for furnace work) part of
the standard equipment for stove testing, either for formal protocol
testing or for more simple testing at our workshops and factories?
2. Is this "turbulance" and "forced air" (flame height and color)
information telling us something about the "fan-jet" or "vortex"
stoves like Philips-FA and the Biolite and the RTI FA stove tested in
Kenya and others with STRONG forced air. The Kenya study (presented
by Mike Sage at GACC Forum) found that the emissions were not as low
as were hope for stoves with fans. Is it possible that the extra
turbulence of those stoves is actually working against their lowering
of emissions?
To me, this is BIG and I hope that CSU and Tami and Aprovecho and
testing centers can check on this with modeling and testing. (or is
this basic knowledge in some specialist fields? )
Be sure to read Alex's message below if you have not already done so.
Paul
Paul S. Anderson, PhD aka "Dr TLUD"
Email:[email protected] Skype: paultlud Phone: +1-309-452-7072
Website:www.drtlud.com
On 4/14/2013 8:59 PM, Alex English wrote:
Yes, in the stoves world TLUDs with fans are comparatively clean
burning. I'm just saying it doesn't necessarily follow that they are
at their best when their flame is shortest.
Any burner will have a range of emissions including a sweet spot
where it performs best. There are lots of variables to consider. Some
require better instrumentation.
For a TLUD with a fan, or a boiler with a fan, you can shorten the
flame with extra secondary air. As you know, if it isn't needed for
combustion then is robs heat, that may be needed for optimum
combustion. Yes long/tall flames can have sooty tips. So there are
potential trade offs. When I can see the flame and my combustion
analyser at the same time I have often seen that a long flame has
lower CO/CO2, less excess air and higher heat transfer efficiency.
Not enough air and it will be even longer with poorer emissions.
Flame colour is a clue, its the numbers that inform. Better mixing
from higher pressure blowers/fans can shift the range of flame
lengths shorter. Stated another way, the optimum flame length is
unlikely the shortest.
I'm being warmed by my ND pellet stove right now. After the secondary
air ports the flame travels horizontally through a 2.5 inch tube, 12"
long. For this firing rate the sweet spot is when the flame fingers
are shooting out six inches past the tube end. More secondary air
shortens it back inside the tube. Less secondary lengthens it and
turns it more orange and larger. CO/CO2 increases in both cases.
There will be no visual emissions from the chimney for any of these
scenarios. Real time PM and NOx numbers might enlighten this tale some.
I've seen a large chip boiler cut its CO in half improve 4% points
of thermal efficiency just by closing some secondary air ports. The
flame lengthened by roughly 25%.
Years ago when I was testing my Reed style fan TLUD on low power. It
had the smallest of flames but the flame didn't fill the chamber
cross section of the chamber below the pot. Some of the pyrolysis
products were sneeken past the flame and condensing brown (not soot)
on the pot. Less secondary air, a larger flame, and perhaps a
different geometry could have helped. The problem went away at higher
firing rates with a bigger and somewhat taller flame.....
....but I burnt the food and went hungry:(
Alex
On 14/04/2013 5:18 PM, Lanny Henson wrote:
A response from Alex English! made my day.
Fan powered TLUDS have a nice short flame height, are they not clean
burning?
Lanny
----- Original Message -----
*From:* Alex English <mailto:[email protected]>
*To:* Discussion of biomass cooking stoves
<mailto:[email protected]>
*Sent:* Sunday, April 14, 2013 2:25 PM
*Subject:* Re: [Stoves] Airflow For Biomass Fired Appliances-
Natural Draft Stoves
Lanny,
I understand the comment below but I think flame height can be
shortened with excessive excess air. The lowest emissions CO/CO2
and highest temperatures, at some power levels, in appliances
that I have tested has often been when there is a significantly
taller tail of flame.
However, don't believe all tall tails :)
Alex
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