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<div class="moz-cite-prefix">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.<br>
<br>
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.<br>
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.<br>
<br>
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.<br>
<br>
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%.<br>
<br>
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.....<br>
....but I burnt the food and went hungry:(<br>
<br>
Alex<br>
<br>
<br>
<br>
<br>
On 14/04/2013 5:18 PM, Lanny Henson wrote:<br>
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<div><font size="4">A response from Alex English! made my day.</font></div>
<div><font size="4">Fan powered TLUDS have a nice short flame
height, are they not clean burning?</font></div>
<div><font size="4">Lanny</font></div>
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<div style="FONT: 10pt arial">----- Original Message ----- </div>
<div style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color:
black"><b>From:</b> <a moz-do-not-send="true"
title="english@kingston.net"
href="mailto:english@kingston.net">Alex English</a> </div>
<div style="FONT: 10pt arial"><b>To:</b> <a
moz-do-not-send="true"
title="stoves@lists.bioenergylists.org"
href="mailto:stoves@lists.bioenergylists.org">Discussion of
biomass cooking stoves</a> </div>
<div style="FONT: 10pt arial"><b>Sent:</b> Sunday, April 14,
2013 2:25 PM</div>
<div style="FONT: 10pt arial"><b>Subject:</b> Re: [Stoves]
Airflow For Biomass Fired Appliances- Natural Draft Stoves</div>
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<div class="moz-cite-prefix">Lanny,<br>
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. <br>
<br>
However, don't believe all tall tails :)<br>
Alex<br>
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