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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;mso-fareast-language:EN-US'>Dear Kirk<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'>This is the sort of detailed analysis that really helps the whole field of advanced stoves. I really appreciate your taking the time to put it into writing.<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'>Method three, turned upside down, is a downdraft stove with preheated secondary air and it is a very good way to burn biomass, especially pellets which are predictable. There is no need to elevate the fuel because gravity handles that. I can recommend that anyone trying it use a wire grate, not bars. This is a development of the BLDD stoves from the SeTAR Centre where considerable success has been achieved in reducing PM emissions burning semi-bituminous coals and again in Mongolia burning wet lignite, both with extremely low emissions. <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'>Method 2 – using flamelets to maintain the main fire is a useful idea that can be added to many stoves to overcome some debilitating shortfalls (ie make them practical devices). <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'>Can I assume, based on your report, that you do not own a combustion analyser? You have long ago reached the stage where you need one to be able to make better prototypes and to be able to make more generalised statements. Some of the things said in the document are only correct in certain cases. In nearly all stove layouts, if there is air entering from below and exiting the top, the excess air level is too high to get really good results save in narrow circumstances (low variability). If you want to have high turndown, you have to control the EA in order to have a flame remain viable. <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'>In the case of the flamelets, part of the reason for your success is that the flamelets are compensating for too much excess air in a turned down condition. If the EA was lower, the flamelets would perhaps be ‘less necessary’. <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'>You described having up to three controllable air sources. What I have been suggesting is that the control of the secondary air can be made automatic if the bottom-in-top-out architecture is abandoned in favour of downdrafted preheating. You are correct, you need three controls, but if the structure is correct, that happens automatically because the heat inside controls the amount of air entering. With a bottom-to-top air path, there is nearly no hope of getting that to happen automatically. <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'>With the downdraft layout, there is a lot to be gained in terms of automatic control because all air is downdrafted to the fire chamber. A combination would be downdrafting secondary air, possible the pilot flame air as well, in the amounts needed to cover the range of power envisaged. The draft calculator available on the Stoves website can assist with this while only having a thermocouple to measure gas temps with. You divide the stove into sections and enter the temps are the top and bottom of each and it will calculate the total draft. You can either check the draft of something that works well, or predict what temps or heights you need in order to generate the draft necessary to run the stove at that 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'>I really encourage you to get or borrow a combustion analyser and read the article in Boiling Point on how to use and calculate the necessary numbers that provide guidance. <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><o:p> </o:p></p><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Crispin,</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"'>Attached is the document which introduces the turn-down methods I have been looking at. </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"'>My comparison is that all three stoves, the Peco Pe, Vesto, and Prime stove introduce air lower in the reactor from holes in the reactor wall, directing air at the char. The Method 2 arrangment introduces the air high in the reactor, just under (2.5 cm) the secondary air entrance. This air combusts wood gas forming a pilot flame just under the secondary flame. The way it works is that the pilot flame supports the secondary flame, keeping it hot and maintaining flame presence which enables the secondary flame to survive turn-down. The functions of the two methods, blowing air on the char vs. forming this pilot flame are very different. Method 2 at first seems unlikely to work. When I first saw it, I was surprised and upset because I could not see how it could work. It happened by chance. I was testing Method 1 to see what was the best sequence for adjusting the three controls to lower the flame. I tried several sequences. Then I tried opening the secondary air control and then reducing the early secondary air to form a small flame (this small flame acted as the pilot flame). I reduced the primary air. To my surprise and shock, the secondary flame reduced to a strong medium sized flame. Usually the secondary flame becomes unstable and produces smoke before an early secondary flame appears at the char. I reduced the primary further and the secondary flame reduced even further, still no smoke. I kept reducing it until the small secondary flame finally became unstable. I was very upset because I had been working on Method 1, producing an early secondary flame at the char for over a year and here was a stable and small secondary flame. I felt like my work was a waste if the secondary flame can be stable during turn-down. In time I realized that this was a seperate method for turn-down, and it became Method 2. Methods 3 and 4 were found later in a similar manner, by chance while doing tests on Method 1. I did not predict or plan these methods, I only found them by chance. I found Method 1 by chance also, while doing tests with spinning the air forming a vortex, and I noted the spinning air sometimes descended into the stove and kept the flame alive even when I shut the primary air off. I saw that the flame could be kept alive with air from above and this led to Method 1.</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"'>The four methods are shown in the attached document. I will be at stove camp at Aprovecho in July and will demonstrate all four methods then.</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"'>Thank you for your interest,</span><o:p></o:p></p></div><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Respectfully,</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"'>Kirk Harris</span><o:p></o:p></p></div><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Santa Rosa, CA. USA</span><o:p></o:p></p></div></div></body></html>