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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 Marc<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'>The primary problem is that side-fed stick burning stoves typically have no primary air control. Unless the air is brought under control, there is no easy way to address the issue of excessive excess air (if that is a permissible phrase).<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'>The approach taken with the traditional Keren stove which is being improved by GERES and YDD in Indonesia (very popular clay product) is to limit the airflow using the pot-stove clearance. This sets a limit on the total air flow without making any improvement to the way secondary air is added – and it literally costs nothing to implement. The pot becomes part of the combustion chamber, basically.<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'>Adding jetted (fan as per U Colorado experiments or natural draft) to a fire that already has too much air is going to increase PM and CO under some power conditions. The solution is to limit the ingress of air. <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'>Making a stove taller to create the draft needed for useful secondary injection only adds to this requirement, though it can create the necessary mixing. Secondary air should only be added to a stove that is running short of air, and the designer should deliberately create the conditions in the chamber where there is such a shortage. That is why the TLUD gasifiers are so clean – there is almost no way to get excess air into the primary gas output. In a way it is accidental. When secondary air is added, presto: good burning conditions with low EA.<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'>A fire running with an open door is begging for there to be too much excess air. The Rocketworx stove (which is a bit of a misnomer because it is not a true ‘rocket stove’ as usually defined) addresses this quite well. It has no air control door, but achieves the purpose anyway by departing significantly from the recommended Rocket Stove dimension set. It also has preheated secondary air and a small amount of tertiary or finishing air. And the result is still a low enough excess air level at high power.<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'>As a result, the combustion seems pretty good and the fire-to-pot heat transfer efficiency can exceed 40%. For an ‘uncontrolled’ stove (nothing to adjust) this is quite high. The key is control over the excess air level.<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'>That said, I have seen test results for a liquid fuel stove with a 72% heat transfer efficiency at both high and low power. That is unusually good. It too is ‘uncontrolled’ save for the evaporator handle that sets the power level. As a result, the CO level is very low at all powers. A really good gasifier should be in that range, in my view. <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'>Regards<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'>Crispin<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'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'> Stoves [mailto:stoves-bounces@lists.bioenergylists.org] <b>On Behalf Of </b>Marquitusus<br><b>Sent:</b> Friday, May 22, 2015 08:54<br><b>To:</b> stoves@lists.bioenergylists.org<br><b>Subject:</b> [Stoves] Secondary air in Rocket Stoves?<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'>Hi to all,<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'><o:p> </o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'>In the ETHOS 2015 Dean Still's presentation he states that:<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'><o:p> </o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'>"<i>In a Rocket stove only forced air mixing results in almost complete combustion. Strong jets of air are needed to fully mix the air, flame, smoke, and gas. Adding a chimney to a Rocket stove doesn’t result in the forceful jets that create adequate mixing. Adding height to the Rocket combustion chamber, while giving more time for combustion to occur, also draws in more cold air that results in more wood being burnt</i>."<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'><o:p> </o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'>I was wondering if this "forced air mixing" should came from natural draft. For example, at some distance above the combustion zone, we can make some holes in the chimney allowing secondary air to enter and mix with the hot gases, creating a secondary combustion zone. Maybe we can put a "concentrator ring" above the holes like in a TLUD to create some turbulence.<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'><o:p> </o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'>This done, we can also increase the chimney height without the problem of "drawing more cold air that results in more wood being burnt", as part of the increased draft suction will be used to pull the secondary air inside the chimney.<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'><o:p> </o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'>With this tall chimney, hot gases can have more "mixing, time and temperature" to achieve the desired complete combustion.<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'><o:p> </o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'>Anyone tried something like this?<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'><o:p> </o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'>Some questions arising:<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'>- What distance above the primary burning zone should we put the secondary air?<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'>- What number and size should be secondary air holes? (we can take experience from TLUDs)<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'>- What size should be the concentrator ring? (we can take experience from TLUDs)<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'>- What height should be the chimney after the concentrator ring?<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'><o:p> </o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'><o:p> </o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'>Marc<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:"Calibri",sans-serif'><o:p> </o:p></span></p></div></div></div></body></html>