<font color="#333399"><font><font face="tahoma,sans-serif"><b>It could be burning of hydrogen. At that temperatures probably you are getting some syngas and purple is a combination of red and blue (reddish flame is characteristic of hydrogen).</b></font></font></font><div>
<font color="#333399"><font><font face="tahoma,sans-serif"><b><br></b></font></font></font></div><div><font color="#333399"><font><font face="tahoma,sans-serif"><b>Cheers.</b></font></font></font></div><div><font color="#333399"><font><font face="tahoma,sans-serif"><b><br>
</b></font></font></font></div><div><font color="#333399"><font><font face="tahoma,sans-serif"><b>Anil</b></font></font></font></div><div><font color="#333399"><font><font face="tahoma,sans-serif"><b><br></b></font></font></font><br>
<div class="gmail_quote">On Mon, Sep 24, 2012 at 7:29 PM, Crispin Pemberton-Pigott <span dir="ltr"><<a href="mailto:crispinpigott@gmail.com" target="_blank">crispinpigott@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div lang="EN-CA" link="blue" vlink="purple"><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Dear Dean<u></u><u></u></span></p><p class="MsoNormal">
<span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">I think it has something to so with the rate of the pyrolysis of the final portion of the fuel. When the zone reaches the bottom, and there is metal there, the pyrolysis rate of the final portion of fuel is at a higher rate than any equal mass during the rest of the burn.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">As a result, the composition of the gas changes because the reaction rate is different. There is no fuel below the ‘final bit’ to absorb heat (esp from drying the fuel below) and also there is no rising moisture from the fuel below. Hot water vapour is highly reactive and changes the gas composition by changing the reaction speed.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">I have also notice the change in colour and have a few photos. Do you suppose it can be used as an indicator to the cook that the ‘end is near’?<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Early fire, highest moisture level<u></u><u></u></span></p>
<p class="MsoNormal"><img width="416" height="447" src="cid:image001.jpg@01CD9A3B.4458A320"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u><u></u></span></p><p class="MsoNormal">
<span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Middle fire, constant moisture level<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><img width="416" height="422" src="cid:image002.jpg@01CD9A3B.4458A320"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u><u></u></span></p><p class="MsoNormal">
<span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Late fire, low moisture level, highest pyrolysation rate, higher carbon burning portion<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><img width="416" height="434" src="cid:image003.jpg@01CD9A3B.4458A320"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u><u></u></span></p>
<p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Notice that the purple flame is always there, and it is always at the point of secondary air entry. This indicates that is may be more related to the carbon burn (CO) than any of the speculation above. The overall impression is influenced by the bright white emissions from particles. As the volatiles are burned away, there are very few particles and the white disappears (or yellow if it is not a very hot fire). Thus the ‘change in colour’ might be more because the PM disappeared along with the light, than the presence of a new colour. The impression on the eyes would be the same in both cases.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Best regards<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Crispin<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal">Hi Stovers!<u></u><u></u></p><div><p class="MsoNormal"><u></u> <u></u></p></div><div><p class="MsoNormal">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.<u></u><u></u></p>
</div><div><p class="MsoNormal"><u></u> <u></u></p></div><div><p class="MsoNormal">Any ideas?<u></u><u></u></p></div><div><p class="MsoNormal"><u></u> <u></u></p></div><div><p class="MsoNormal">Best,<u></u><u></u></p></div>
<div><p class="MsoNormal"><u></u> <u></u></p></div><div><p class="MsoNormal">Dean<u></u><u></u></p></div></div></div><br>_______________________________________________<br>
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