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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Thanks Dale.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">For the reasons you give, I expect the upper limit of the efficiency will be dominated by the excess air level. It could be easily demonstrated by placing something over the fuel entrance chute to
limit the total air flow for any given power. Watching the O2 level, progressively reduce the air volume entering the chute.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">As the flow reduces, the EA level will reduce to some point at which there is an obvious increase in smoke. That will depend on the architecture so there is no magic number but probably by the time
O2 reaches 7% for an EA value of 50%.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Although the type of combustion is different, the Kyrgyzstan version KG4.2 of the Model 4 coal pyrolyser has this same problem with air and the hopper.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Unlike a downdraft stove with a ‘restrictor plate’ type cover (with an adequate hole in it) the KG4.2 closes the hopper completely and has all the air enter from underneath the grate. The upper portion
of the hopper is full of unburnable gases (not enough air) and combustion is restricted to the lowest portion of the hopper. There is an air control door on the air supply.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">If one wants to refuel the hopper, the air control door is first closed, the hopper door opened very slightly (1 or 2 mm) and all the smoke is drafted down into the hopper and burns in the fire.
After about 30 seconds the hopper is cleared of gases and it can be opened without contaminating the room.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">This is so effective as a technique for keeping the room clean that Prof Soorenbaev was able to identify those homes he was surveying (with micro-PEMS) that were not implementing the instructions
properly, and Ulan sent the trainers back for another visit.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">If you need help on how to do this, have a look at the
<a href="http://www.newdawnengineering.com/website/library/Stoves/Kyrgyzstan/KG%20Model4-Coal/">
drawings</a> or write. Also check the TJ4.0 (artisan) version. There are photos at both locations.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">One more thing: as the EA drops the heat transfer efficiency will rise, probably leaking around the high 30’s. At some point the emissions will be at a minimum. That minimum only applies to that
particular power level, unfortunately.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Regards<br>
Crispin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span lang="EN-US">I can address some of these questions.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">With the right balance of flow passage sizes and the correct dimensions, the flame and smoke are almost always swept down the feed chute and into the fire. The only exceptions are if there is a strong wind from the wrong
direction, or if the wood is burning right at the inlet to the fuel chute. It’s rather spectacular to watch fire and smoke very close to the chute inlet; it looks like they should be escaping from the stove, but they are sucked down into the stove.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Early designs of the stove has much shorter pot supports, restricting the flow and causing a lot of fire to come out the fuel chute. I think there is a photo of this in the students’ report. So, if you don’t get the
dimensions right, the stove performs poorly. <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">The flow passages are large at every point, so I expect there is indeed a lot of excess air. Efficiency is typically about 20%, not horrible but not great. I’m reluctant to make the fuel chute smaller because it would
restrict the size of fuel that could be used. I’m reluctant to make the pot support gap smaller because that’s likely to lead to more smoke. A smaller riser diameter would mean less power. There’s probably a way to vary the dimensions to get less excess
air without sacrificing something else, but I don’t see how at this point. <o:p>
</o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Dale<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> Stoves [<a href="mailto:stoves-bounces@lists.bioenergylists.org">mailto:stoves-bounces@lists.bioenergylists.org</a>]
<b>On Behalf Of </b>Crispin Pemberton-Pigott<br>
<b>Sent:</b> Wednesday, May 17, 2017 11:04 AM<br>
<b>To:</b> Andreatta, Dale A. <<a href="mailto:stoves@lists.bioenergylists.org">stoves@lists.bioenergylists.org</a>>; Discussion of biomass cooking stoves <<a href="mailto:stoves@lists.bioenergylists.org">stoves@lists.bioenergylists.org</a>><br>
<b>Cc:</b> <a href="mailto:gerding.28@osu.edu">gerding.28@osu.edu</a>; <a href="mailto:lackey.69@osu.edu">
lackey.69@osu.edu</a>; McTurner, Sam <<a href="mailto:mcturner.4@buckeyemail.osu.edu">mcturner.4@buckeyemail.osu.edu</a>>;
<a href="mailto:haemmerle.12@osu.edu">haemmerle.12@osu.edu</a>; <a href="mailto:sharkey.50@osu.edu">
sharkey.50@osu.edu</a><br>
<b>Subject:</b> Re: [Stoves] Downfeed burner student project<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D">Dear Dale<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D">Another great experiment from you. You always have something substantial to report. <o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D">'Back in the day', this type of stove (shown in the Village Technology Handbook) was being tried at Aprovecho in 1982. David Hancock (the famous) was there
for a year working on it. Two things come to mind from his description of its inherent design issues. <o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D">One is that the fire tends to burn back into the fuel feed area with predictable consequences. This is enhanced at low power. How has this been addressed
in the latest work? David addressed it by inventing the Rocket Stove as we know it now, something affirmed by both David and Larry W, with horizontal feeding. <o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D">The then head of Aprovecho Ianto Evans addressed it by going to a vertical feed with high power only, basically, in his Rocket Mass Heaterý, still being
promoted especially by the Cob House community. The smoke and flames are 'held in' by the high air velocity. <o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D">Next is the question of excess air. ýIf you have managed to keep all the smoke and fire in the combustion area, has this been done at the cost of increasing
the excess air level? What is the O2 concentration in the exhaust?<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D">An inherent problem with the standard Rocket Stove dimensions as recommended is a high EA level with low gas temperature, limiting the maximum cooking efficiency.<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D">As you have very good low power operation I am interested to know how these issues have been addressed. A lot of people could benefit from new solutions. <o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D">Thanks<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D">Crispin <o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span lang="EN-US" style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:"Times New Roman",serif">ý<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">A number of people around the world have been working on downfeed rocket stoves, stoves with fuel chutes sloped at about 45 degrees but not vertical. I believe this is a excellent basic design. I’ve worked with the
InStove downfeed burners for institutional stoves and was very impressed. Recently, a group of students at The Ohio State University worked on a project for a family size downfeed stove.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">A picture is attached, as well as their final presentation. A link to a short video is:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><a href="http://www.youtube.com/watch?v=VJcnp5lE_fg">www.youtube.com/watch?v=VJcnp5lE_fg</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">The “l” above is a lower case letter ell.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Like the normal rocket stove with horizontal fuel feed, the stove is easy to light, the fire is concentrated so that the smoke had a good chance of being consumed in the fire, the insulation keeps the heat in, allowing
for good combustion of wet wood and easy rekindling of the fire when it gets weak. The downfeed burner is an improvement, I believe, because it’s easy to see the fire and because the fuel sometimes self-feeds as the tips of the sticks burn away. (This depends
highly on the shape of the wood; I would hesitate to call a downfeed burner a self-feeding stove, but sometimes it self feeds.) I did a test recently where I simmered a pot with a lid for over an hour without touching the stove at all. Two sticks of about
5 cm diameter burned and to end, self-feeding occasionally, and even when they didn’t the fire burned strongly and was pulling down the chute. Of course, simmering with a lid is much easier than without.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">The students’ stove has a large diameter riser, 15 cm, which leads to high power but perhaps lower efficiency. Time to boil 5 liters was about 20 minutes for the students, but I’ve been pushing the stove harder and getting
11-15 minutes. I think more people want high power than high efficiency, so I pushed the students to use the larger riser. Smoke seems to be minimal unless the fire is large, about like any other stove.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">The students developed a unique skirt design, designed to be ideal for a large pot, but workable for any pot, with or without handles. The fuel chute is rather large, and works for wood up to 6 cm in diameter. Again,
I pushed them to have a large fuel chute and we are perhaps sacrificing a little efficiency for usability, being able to burn larger wood.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Between tests with the InStove unit and with my students’ work, the downfeed burner seems to be very good at burning wet wood, though more tests need to be done. I intend to do these tests in the summer, and will report
my findings by ETHOS-time. I’ll also try some design changes, starting with a cone-shaped pot support and a different type of skirt. I expect to be ready to report on all this by ETHOS-time.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Dale Andreatta<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><a href="mailto:dandreatta@sealimited.com">dandreatta@sealimited.com</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Mechanical Engineer and Adjunct Professor<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">The Ohio State University<o:p></o:p></span></p>
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