<div dir="ltr"><div class="gmail_default" style="font-size:small">Crispin,</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">Thanks for your always helpful advice.</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">For widespread adoption, we sometimes must sacrifice efficiency for simplicity. With the cooking hole, that probably means using bricks without curves.</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">The cooking hole is new and I hope others test variations. Here is a <a href="https://drive.google.com/file/d/1Wn-wudQ_5InNPaKrSi6MtJS2rUvjeaKi/view?usp=sharing">video</a> of one cooking hole heating two cookpots. We found it was smoky without the hole between the bottom bricks, </div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">As a reminder, the cooking hole is a 22x22x24 hole in the ground. The fuel is piled up so the top is 10 cm above ground. Sticks and maize stalks are stacked in a criss cross manner to allow air to flow within the fuel pile. The pile is lit on top. It burns down without tending for 30-90 minutes without adding fuel. Water in both pots boils in about 15 minutes and simmers for the rest of the 30-90 minutes. I am told that the visible smoke is much less than from firewood in unmodified three stone cookstoves.</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small"><img src="cid:ii_l5ws2dr51" alt="Youtube Photo.jpg" width="280" height="210" style="margin-right: 0px;"><br></div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">I think custom bricks that are not fired in a kiln ("unburnt bricks") will harden while cooking meals. We are testing this and I'm optimistic. Ripple Africa has found that their unburnt bricks harden while cooking. And our custom bricks that line the cooking hole are starting to harden. Using custom, unburnt bricks to support cookpots will allow us to determine the best dimensions and just distribute molds. Our networks make the distribution of molds in Africa and local production of the custom bricks easy. It sounds like they should be about 10 cm high so that two bricks will elevate the cookpot 10 cm above the top of the fuel pile.</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">Kevin</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Jul 22, 2022 at 6:16 PM Crispin Pemberton-Pigott <<a href="mailto:crispinpigott@outlook.com">crispinpigott@outlook.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<div name="BB10" id="gmail-m_3435013736166534654BB10_response_div_BBPPID" dir="auto" style="width:100%">Dear Kevin</div>
<div name="BB10" id="gmail-m_3435013736166534654BB10_response_div_BBPPID" dir="auto" style="width:100%"><br>
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<div name="BB10" id="gmail-m_3435013736166534654BB10_response_div_BBPPID" dir="auto" style="width:100%">I looked into this when developing the Vesto and there are two answers. One is the correct height (minimum?) Above the fire to get good draft to pull air into the fire at a high enough
velocity to get good mixing, and the flame space needed to complete combustion. </div>
<div name="BB10" id="gmail-m_3435013736166534654BB10_response_div_BBPPID" dir="auto" style="width:100%"><br>
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<div name="BB10" id="gmail-m_3435013736166534654BB10_response_div_BBPPID" dir="auto" style="width:100%">For wood, I found the vertical space needed is at least 100 mm, with a preference for 110 mm, and for charcoal 50 mm with preference for 60 mm. </div>
<div name="BB10" id="gmail-m_3435013736166534654BB10_response_div_BBPPID" dir="auto" style="width:100%"><br>
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<div name="BB10" id="gmail-m_3435013736166534654BB10_response_div_BBPPID" dir="auto" style="width:100%">You drawing shows two parallel rows of bricks. This should be two semi-circles in order to limit drawing in useless air. Cooling the flame with unnecessary excess air is a major cause
of PM with wood stoves and CO in charcoal stoves. </div>
<div name="BB10" id="gmail-m_3435013736166534654BB10_response_div_BBPPID" dir="auto" style="width:100%"><br>
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<div name="BB10" id="gmail-m_3435013736166534654BB10_response_div_BBPPID" dir="auto" style="width:100%">Having a fuel hole and an air hole is important, closing everything else if possible. Putting a stone/pebble grate as you have been, is a great help. That allows incoming air to burn
the accumulating char, raising the combustion temperature. That of course reduces all emissions from incomplete combustion. </div>
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<div name="BB10" id="gmail-m_3435013736166534654response_div_spacer_BBPPID" dir="auto" style="width:100%">Sheltering a fire on three sides is so-o much better than two parallel walls. So if they have bricks, even mud bricks as are common in the Eastern Cape, the result can be pretty
good. </div>
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<div name="BB10" id="gmail-m_3435013736166534654response_div_spacer_BBPPID" dir="auto" style="width:100%">As a general rule, put the air entrance at the back bottom, opposite the fuel entrance, not on the same side as per rocket stove. It will keep the flame centered and away from the
walls. That plus >100 mm flame space will give a reasonable result. </div>
<div name="BB10" id="gmail-m_3435013736166534654response_div_spacer_BBPPID" dir="auto" style="width:100%"><br>
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<div name="BB10" id="gmail-m_3435013736166534654response_div_spacer_BBPPID" dir="auto" style="width:100%">Keep up your good work!</div>
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<div name="BB10" id="gmail-m_3435013736166534654response_div_spacer_BBPPID" dir="auto" style="width:100%">Regards </div>
<div name="BB10" id="gmail-m_3435013736166534654response_div_spacer_BBPPID" dir="auto" style="width:100%">Crispin </div>
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<div id="gmail-m_3435013736166534654from"><b>From:</b> <a href="mailto:kmclean56@gmail.com" target="_blank">kmclean56@gmail.com</a></div>
<div id="gmail-m_3435013736166534654sent"><b>Sent:</b> July 22, 2022 9:41 AM</div>
<div id="gmail-m_3435013736166534654to"><b>To:</b> <a href="mailto:stoves@lists.bioenergylists.org" target="_blank">stoves@lists.bioenergylists.org</a></div>
<div id="gmail-m_3435013736166534654reply_to"><b>Reply to:</b> <a href="mailto:stoves@lists.bioenergylists.org" target="_blank">stoves@lists.bioenergylists.org</a></div>
<div id="gmail-m_3435013736166534654subject"><b>Subject:</b> [Stoves] Space between biomass fuel and cookpot in an open-fire cookstove</div>
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<div class="gmail_default" style="font-size:small">What is the minimum distance from the top of the fuel to the bottom of the cookpot? I've heard that 8 cm is the minimum to get the best combustion.</div>
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<div class="gmail_default" style="font-size:small">We are training cooks to use common bricks to elevate two cookpots over one cooking hole. I want to make sure the cookpots are high enough.</div>
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