Hi Alex,<div><br></div><div>I experience that if there is the right amount of secondary air the flame above the pile is sustained during the switch from burning wood to burning bio-char even though the bottom of the pile is not yet glowing orange. Maybe you're right that the tar is burning later when the bottom has fully caught fire that gives the blue flame a reddish tinge. Good idea!</div>
<div><br></div><div>Ron: Maybe we have to burn the bio-char to get above 45% thermal efficiency which is Tier 4 in the IWA metrics? I think it's great that a TLUD can be tuned to either save or burn the bio-char to meet the needs of the consumer, say urban vs rural?</div>
<div><br></div><div>Best,</div><div><br></div><div>Dean<br><br><div class="gmail_quote">On Sun, Sep 23, 2012 at 6:29 PM, Alex English <span dir="ltr"><<a href="mailto:english@kingston.net" target="_blank">english@kingston.net</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<div>Hi Dean,<br>
I'm a bit confused by your first sentence. You seem to be
suggesting that there is a blue flame before the bottom is bright
orange. <br>
<br>
Tell me if this makes any sense.<br>
<br>
In a TLUD the bio-char doesn't start to burn until the pyrolysis
front reaches the bottom. At that time the bottom is glowing
bright orange and char oxidation is taking place. The hot CO2
formed at the bottom then may reduce to CO as it passes hot carbon
above the bottom layer. This CO can then burn with additional air
in a blue flame above.<br>
<br>
This is somewhat stove dependent but there can be some tar
condensation on the fuel chamber walls during pyrolysis. During
the char burning phase and perhaps in this case at the end when
the top of the char pile is radiant orange, this layer of tar
could re-volatize and mix with the CO to form a higher energy
flame with a reddish component. It would also be helpful if we
knew what the excess air values were during these phases.<br>
<br>
My two sense,<br>
<br>
Alex<br>
<br>
On 23/09/2012 8:10 PM, Dean Still wrote:<br>
</div>
<blockquote type="cite">Hi Stovers!
<div><br>
</div>
<div>I've been noticing a shift from blue flames above the burning
bio-char in a TLUD to purple flames nearer the end of the burn
when the bottom of the pile is glowing bright orange. I suppose
that the blue flame is caused by burning CO but I wonder why the
purple forms after the blue? The blue self sustaining flame
doesn't heat the water in the pot as well as the purple flame
phase although the pile of bio-char is fully ignited at that
time and may account for the more rapid rise in water
temperature.</div>
<div><br>
</div>
<div>Any ideas?</div>
<div><br>
</div>
<div>Best,</div>
<div><br>
</div>
<div>Dean</div>
<br>
<fieldset></fieldset>
<br>
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