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</o:shapelayout></xml><![endif]--></head><body lang=EN-CA link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Dear Otto<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='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:#1F497D'>></span><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>Is such a stove to complicatied or expencive for the low income households of Africa?<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Tahoma","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'>A stove with preheated primary necessarily means controlling the air. If the stove has a door, or a system of down-drafting the primary air in a preheater (usually made of metal) then it is possible. With no control, any amount of air can access the fire so fuel moisture will be a problem.<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'>The simplest method I know of is to put a metal shell around a combustion chamber. That is not complicated and is accessible to low income families.<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='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>If you put a natural draft gasifier in an enclosure to get the primary air prehated using dry fuel, I would guess that you could use fuel of higher moisture content, later on. <o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Tahoma","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'>Yes, you have to start the fire with kindling. If in the case of the Peko Pe the fuel it directly ignited, and it was wet, it would mean putting some other fuel on too first to get the top layer dried.<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'>All the natural draft gasifiers that I have ever seen are controlled-air stoves, either by design of the air holes, or by the fuel ad how it admits air because of how it packs into the chamber.<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='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>I understand that very dry fuel might burn so fast, that PM might enter the indoor air.<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Tahoma","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'>That is true if the primary air is allowed to enter freely, or if the combustion chamber => air supply has a positive feedback character. For example if you have a self-heating retort where the fire heats the fuel more, making a bigger fire, heating the fuel more, that is going to be a problem because it is self-accelerating. At some point it will run out of primary or secondary air. Whatever the device, either dry fuel or wet fuel will cause a problem if it cannot be adjusted.<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'>Thus designing for the available fuel is important. You can’t develop a stove using dry fuel and expect it to perform predictable with wet fuel. There are many examples of that in the field, unfortunately. Stoves that have <i>some</i> form of air control are able to burn wet and dry fuel on condition that enough wet fuel can be put into the chamber at once. You need to have more fuel involved if it is wet – a physically larger fire. If the chamber is designed for dry wood it can be much smaller, doesn’t need much air preheating, and needs better excess air control, and can outperform any wet fuel stove.<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:10.0pt;font-family:"Tahoma","sans-serif"'>I also think a fan driven gasifier might speed up that process and make it even worse?<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Tahoma","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'>A fan is just a power driven chimney so include fans and chimneys. Does increasing the draft make combustion worse? Depends on the stove! A fan is no panacea, that is for sure. <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></div></body></html>