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<p>Andrew,</p>
<p>Thank you for this response! It is very helpful for me. <br>
</p>
<p>Yes, we would need more experience with the stones to get a
better feel for how it works. As is, my response to Dr. Larson's
statement is hypothesis, which hopefully will be corrected if
needed.</p>
<p>I also recall another question Dr. Larson raised with me some
time ago, wondering why the migratory pyrolytic front produces so
much CO. Reduction of CO2 into CO could add some understanding to
this. There is a lot of hot charcoal available to do this. The
mpf may be producing CO2, which is reduced to CO by the hot
charcoal. You appear to have helped answer this question for me
as well.<br>
</p>
<p>Kirk H.<br>
</p>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">On 11/13/2019 1:57 PM,
<a class="moz-txt-link-abbreviated" href="mailto:ajheggie@gmail.com">ajheggie@gmail.com</a> wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAPSaZeYsXX5p+wUcVMLfPrPgXmcSn4arvy3a3gAvKZEv5dBauw@mail.gmail.com">
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<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Mon, 11 Nov 2019 at
17:36, Harris, Kirk <<a
href="mailto:gkharris316@comcast.net" target="_blank"
moz-do-not-send="true">gkharris316@comcast.net</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div bgcolor="#FFFFFF">Also, the char which falls to the
ground between the rocks will produce CO, which has air
to burn just below and directly inside the charcoal fuel
stack, helping to keep it very hot. There may be other
advantageous chemical reactions which have to do with
reduction, or the interaction of water vapor, which I
know very little about. Perhaps some or you, like maybe
Crispin, could help with this question.
<div>
<div><br>
</div>
</div>
</div>
</blockquote>
<div><br>
</div>
<div>Crispin must be busy; I'm loathe to comment on Kevin's
work with stones without seeing a cook actually cooking an
everyday meal with charcoal. My experience with cooking
with charcoal is on barbecues and I'm not very competent
at it.</div>
<div><br>
</div>
<div>When I look at char burning in my wood burning, space
heating, stove once all the volatiles have flamed off and
I am just left with a bed of char I note that when the bed
is thin it glows red and there is no discernible flame, if
the bed is thick it still glows red but a blue flame
dances on the top. This fits well with the perceived
wisdom that oxygen molecules dissociate on contact with
hot char and combine to give out a lot of heat and carbon
dioxide, no flame is involved. My thoughts are below and I
welcome comments either way.<br>
</div>
<div><br>
</div>
<div>Spread thinly the char will radiate heat and the
exhaust gases of CO2 and N2 give rise to convected heat.</div>
<div><br>
</div>
<div>As the bed gets thicker less heat can escape and the
particles of char mutually radiate thus less heat is lost
to the outside and the bed becomes hotter and in the
absence of oxygen the endothermic reduction of CO2 to CO
occurs, this cools the bed but the CO given off can then
ignite into the blue CO flame once it contacts secondary
air above the bed.</div>
<div><br>
</div>
<div>The late Dr. Tom Reed suggested that if the char bed
were twenty char particles thick mostly all the char would
be converted to CO.</div>
<div><br>
</div>
<div>So we have conditions in a thin bed where the
temperatures are low and little CO is produced and in a
thick bed contained in a combustion chamber where
predominantly CO is produced. The reduction of CO2 to CO
largely occurs when temperatures are above 800C<br>
</div>
<div><br>
</div>
<div>Most of the time with charcoal stoves we have a mixture
of conditions between these two extremes.</div>
<div><br>
</div>
<div>I'm not sure how the stones might modify conditions to
push the balance either way. If the char is distributed
around the stones then they will interfere with mutual
radiation and possibly lower the temperature leading to
less CO, if they act as a grate, forming a plenum under
the fire then more air will be directed under the fire. <br>
</div>
<div><br>
</div>
<div>I can see that there will be a condition where the
balance of Nitrogen, CO2 and CO is such that the CO will
not ignite even when it meets air as it will be too dilute
in the nitrogen and carbon dioxide mixture. Apart from
being potentially dangerous this represents a lost of heat
from the stove.</div>
<div><br>
</div>
<div>Andrew<br>
</div>
<div> </div>
</div>
</div>
</div>
<br>
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