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<p class="MsoNormal">I can address some of these questions.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Dale<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><b>From:</b> Stoves [mailto:stoves-bounces@lists.bioenergylists.org]
<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. <stoves@lists.bioenergylists.org>; Discussion of biomass cooking stoves <stoves@lists.bioenergylists.org><br>
<b>Cc:</b> gerding.28@osu.edu; lackey.69@osu.edu; McTurner, Sam <mcturner.4@buckeyemail.osu.edu>; haemmerle.12@osu.edu; sharkey.50@osu.edu<br>
<b>Subject:</b> Re: [Stoves] Downfeed burner student project<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="background:white"><span 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 style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span 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 style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span 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 style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span 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 style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span 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 style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span 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 style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span 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 style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span 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 style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span 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 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 style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span 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">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></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">A picture is attached, as well as their final presentation. A link to a short video is:<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal"><a href="http://www.youtube.com/watch?v=VJcnp5lE_fg">www.youtube.com/watch?v=VJcnp5lE_fg</a><o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">The “l” above is a lower case letter ell. <o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">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></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">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></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">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></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">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></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Dale Andreatta<o:p></o:p></p>
<p class="MsoNormal"><a href="mailto:dandreatta@sealimited.com">dandreatta@sealimited.com</a><o:p></o:p></p>
<p class="MsoNormal">Mechanical Engineer and Adjunct Professor<o:p></o:p></p>
<p class="MsoNormal">The Ohio State University<o:p></o:p></p>
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