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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 Sarbagya<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'>Interesting questions as always.<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><p class=MsoNormal><b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>></span></b>However, one conclusion I obtained was that secondary air if not pre-heated would have the tendency to put off the fire by blowing in cold air. <o:p></o:p></p></div><div><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Quite true especially of the environment has high excess air (EA).<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p></div><div><p class=MsoNormal><span style='color:#1F497D'>></span>What is the role of secondary air for wood burning stoves ? <span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Secondary combustion always takes place, it is just that by staging it carefully (in two or three sections) the fuel burn rate can be controlled better and a wider range of moisture and fuel sources can be used. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>It is not that difficult to burn any particular fuel cleanly under constant conditions. But real stoves have varying conditions.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>></span>Is there an optimum gap for the secondary air to travel between the jackets of the combustion chamber before ejecting out into the combustion chamber ? <span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Definitely not. The flow should be ‘adequate’ and the capacity to flow should be slightly higher than the actual flow, that’s all. Remember that flowing air, even if rising while being heated, requires energy. That energy can be concentrated on the inlet to produce a high velocity jet of air rather than a continuous dribble. The higher velocity jet can penetrate into O2-starved gases (list from a TLUD) thus mixing and burning everything well. Things that do not work well with small stoves over a range of conditions include large diameter round gas paths (like 250mm dia) and wide, thin gas paths like 300 wide, 40mm deep. It is difficult to get a clean burn at different burn rates. As cooking stoves pretty much all require power control it means these two approaches are problematic.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>></span>How does this effect the performance of the cookstove ? <span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>What effect?<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>></span>I know a few cookstoves which have secondary air concept included and which seemed to decrease the CO and PM up to some extent. <o:p></o:p></p></div><div><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Even if it is not apparently there, there is secondary combustion (and tertiary combustion) taking place in all flames.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> <o:p></o:p></span></p></div><div><p class=MsoNormal><span style='color:#1F497D'>></span>What is the role of secondary air for charcoal burning stoves ? <span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>It is used to burn the evaporated volatiles (charcoal has lots) and to burn the CO to CO2. It is not uncommon in a charcoal fire (a very hot one) to have CO2 turn back into CO. That CO needs to burned without cooling the gases. If it is cooled to much (which is common with charcoal stoves that have large air holes and no preheating to speak of) the CO remains unburned and is lost. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Many people, writing in many articles, think that charcoal fires ‘make a lot of CO’ – that charcoal is inherently ‘CO-making’. There is nothing special about charcoal. It is just that the stove burning it was not well designed. Most charcoal stoves are not well designed and do not burn the carbon effectively. It is as simple as that. People attribute to the fuel a problem with the stove design. It happens all the time.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>></span>"<span class=apple-style-span><span style='font-family:"Calibri","sans-serif";color:#444444'>Secondary air is necessary to burn charcoal in a low O2 environment at a high temperature." How does this </span></span><span class=apple-style-span><span style='font-family:"Calibri","sans-serif";color:#1F497D'>a</span></span><span class=apple-style-span><span style='font-family:"Calibri","sans-serif";color:#444444'>ffect the performance of the charcoal cookstove?</span></span><o:p></o:p></p></div><div><p class=MsoNormal><span class=apple-style-span><span style='font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>First make the CO and then burn it. It is a good fuel with high energy. Even at a CO/CO2 ratio of 2%, there is a great deal of heat lost to the CO leaving unburned.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Regards<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Crispin<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p></div></div></body></html>