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</o:shapelayout></xml><![endif]--></head><body bgcolor=white 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 Rajan<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'>I watched the demonstration of the stove in use and it looks very nice in terms of materials used and execution.<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'>I have some comments which may help you and others wanting to build this layout of stick-burning 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:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>The grate is similar to the Rocket Stove ‘fuel shelf’ but has the advantage of limiting to some extent the amount of primary air getting to the fuel. This is supplemented by the fact that the grate keeps the hot coals that inevitably fall off the end of the sticks up in the air, not letting them drop to the bottom of the combustion 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><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>The amount of waste charcoal produce is reduced with the grate. The Namibian Tsotso stove uses a similar approach though the grate is not removable. <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 Rocket-type stoves can be improved by adding this type of grate. There are two sources of air in these stoves: the air passing past (under) the far end of the sticks that are burning and the air that enters through the hole into which the fuel is passed. There is a balance needed to get a clean burn.<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'>When you have 3 sticks inserted, you are getting a reasonable burn and a premised flame, basically. Air enters the grate holes vertically and pyrolyses the fuel and the gases are burned above using secondary air that enters with the fuel.<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 point that some secondary air is passing through the grate is correct and it is indeed preheated by the coals burning on it. As you can see, the flames are not ‘finished’ by the time they hit the pot so there is some improvement that can be made in terms of height. Giving more flame space will increase the draft (which affects how much air enters the grate holes) so balance is needed through experimentation. <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 interesting part was your demonstration that when you put in 5 sticks the stove starts to smoke even without a pot (the pot already creates smoke because the flames are touching it). Note, everyone looking at the video, that the fire changes from having a premixed flame to a diffusion flame and there is a change in colour as a result.<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'>This is not the fault of the extra fuel. It is cause by a lack of secondary air which is having to enter through the space where the fuel goes in, and now that space is partially blocked by the additional fuel. The more fuel you add, the more secondary air you need, and the less you get because it is progressively blocked by the fuel. The video clearly shows the two different flame types and the comment is that the ‘flame changes colour’. It has gone from a whole wood burning premixed flame to a wood gasifying diffusion flame because the primary air supply is fixed and the secondary air supply has been reduced.<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'>Reducing the total amount of air in the chamber as also increased the temperature in there! This further accelerates the production of wood gas creating even worse combustion conditions. When the pot is on, the flame has no chance to find oxygen around the top of the combustion chamber (which is the problem of a diffusion flame – the gases are trying to diffuse into the air and find O2). As a result the fire becomes smoky and the CO will rise dramatically. It is a choked fire unable to breathe. The effect is quite reversible as the operator shows.<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'>So the lesson is that the secondary air supply has to be maintained while balancing the burn rate by decreasing the primary air supply to compensate for the increased gas production rate. In general, it is wise to use a grate (probably with fewer total holes) and a drop-down door to close as much air as possible entering with the fuel, then provide secondary air through holes inside the chamber. It is possible to get a balanced combustion at a range of power levels without getting high excess air in the low power condition.<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'>Thanks so much Rajan for sharing the video. It is helpful to show a stove misbehaving as well as working properly.<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 style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0mm 0mm 0mm'><p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> rajan_jiby@dataone.in [mailto:rajan_jiby@dataone.in] <br><b>Sent:</b> Sunday, September 09, 2012 7:24 AM<br><b>To:</b> stoves@lists.bioenergylists.org<br><b>Cc:</b> Paul S. Anderson; Crispin Pemberton-Pigott; mukundan; Sujatha Srini; sudhakar mukundan; vijayaganapathi<br><b>Subject:</b> Wood Stove Demo - Video<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Dear All,</span><o:p></o:p></p></div><div><p class=MsoNormal> <o:p></o:p></p></div><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Here is a demo video of the Servals wood stove attached to the blog.</span><o:p></o:p></p></div><div><p class=MsoNormal><br><a href="http://servalsgroup.blogspot.in/2012/01/servals-modified-natural-draft-wood.html">http://servalsgroup.blogspot.in/2012/01/servals-modified-natural-draft-wood.html</a><o:p></o:p></p></div><div><p class=MsoNormal> <o:p></o:p></p></div><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Regards,</span><o:p></o:p></p></div><div><p class=MsoNormal> <o:p></o:p></p></div><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Rajan</span><o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div></div></body></html>