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</o:shapelayout></xml><![endif]--></head><body lang=EN-CA link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>Dear Julien<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>Relevant to the previous message from me is your comment:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><div><div><div><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>“</span>The burst of wood gas that we often see just before the end of primary pyrolysis is because we are beginning to get char oxidation at the grate. I have measured a sharp increase in temperature 5 cm above the grate (sometimes rising from 750 °C to 1000 °C) when that happens. The rise in temperature accelerates pyrolysis of the residual raw fuel.<span style='color:#1F497D'>”<o:p></o:p></span></p><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>The bottom layer has no air restriction below it and the char tends to burn. That plus the lack of moisture and endothermic volatiles in the fuel that is <i>not</i> below the last layer means the burn rate in the first few layers rises.<o:p></o:p></span></p><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>You can demonstrate the influence of the moisture on this process – the more moisture, the closer the heat gets to the plate before the flash burn starts. The effect is less noticeable with TLUD’s that do not rely on the fuel to restrict the airflow. This was noticed in testing at the YDD Lab in Yogyakarta. Some stoves have the fire expire without much smoke at all (if any) at the end. Others have a clear flash. Those with very well controlled primary air and no easy way for air to evade the controller (by entering from a hole above then flowing downwards through the char, for example) either have no puff or it is small.<o:p></o:p></span></p><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Crispin<o:p></o:p></span></p><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p></div><p class=MsoNormal>Cheers,<o:p></o:p></p></div><p class=MsoNormal>Julien.<o:p></o:p></p><div><div><div><div><div><p class=MsoNormal><br> <br clear=all><o:p></o:p></p><div><div><p class=MsoNormal><br>-- <o:p></o:p></p><div><div><div><div><div><div><p class=MsoNormal>Julien Winter<br>Cobourg, ON, CANADA<o:p></o:p></p></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></body></html>