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<body class='hmmessage'><div dir='ltr'>Very interesting Julian.<br><br>Have you registered (or noticed) any mixing improvement with this prototype over the non counter-current ones? I suppose better mixing shoud be noticed as higher temperatures registered. Have you measured anything like this?<br><br>Marc<br><br><div><hr id="stopSpelling">From: jock@jockgill.com<br>Date: Mon, 25 Jan 2016 20:04:58 -0500<br>To: stoves@lists.bioenergylists.org<br>Subject: Re: [Stoves] Riser Height and a 'Counter-Current' Woodgas Burner - YouTube Vid<br><br><div>Julian,</div><div id="ecxAppleMailSignature"><br></div><div id="ecxAppleMailSignature">Interesting video. </div><div id="ecxAppleMailSignature"><br></div><div id="ecxAppleMailSignature">1. I would try this with a flame retention disc rather than a central hole. I view central holes above fuel bed as a fundamental error. I know central holes are the given wisdom, but I view them as the source of problems that can not be overcome. They are a barrier to better achievements.</div><div id="ecxAppleMailSignature"><br></div><div id="ecxAppleMailSignature">2. I would strive for the maximum amount of blue flame. I did not see any in your video. People want to cook with blue flames. Aspirational.</div><div id="ecxAppleMailSignature"><br></div><div id="ecxAppleMailSignature">3. Perhaps an hour glass type device might work? Could be asymmetrical?</div><div id="ecxAppleMailSignature"><br></div><div id="ecxAppleMailSignature">Cheers,</div><div id="ecxAppleMailSignature"><br></div><div id="ecxAppleMailSignature">Jock<br><br><div><div style="font-family:UICTFontTextStyleBody;">Jock Gill</div><div style="font-family:UICTFontTextStyleBody;">P. O. Box 3</div><div style="font-family:UICTFontTextStyleBody;">Peacham, VT 05862</div></div><div style="font-family:UICTFontTextStyleBody;"><br></div><div><a href="https://plus.google.com/_/notifications/emlink?emr=02164940119180120523&emid=CIn6jOiavboCFcgLTAodARYAAA&path=/102260924343967128597/op/u&dt=1383089746165&ub=50" style="font-weight:bold;background-color:rgba(255, 255, 255, 0);" target="_blank"><font color="#000000">google.com/+JockGill</font></a></div><div><br></div>Extract CO2 from the atmosphere!</div><div><br>On Jan 25, 2016, at 7:10 PM, Julien Winter <<a href="mailto:winter.julien@gmail.com">winter.julien@gmail.com</a>> wrote:<br><br></div><blockquote><div><div dir="ltr">
<p class="ecxMsoNormal">Hi all;</p><p class="ecxMsoNormal"><br></p><p class="ecxMsoNormal">I have posted a video on YouTube on Riser Height and a 'Counter-Current' burner that continues on the theme of discussions earlier this month about premixed flames.<br></p>
<p class="ecxMsoNormal"> </p>
<p class="ecxMsoNormal"><a href="https://youtu.be/KzYUzJPM3eQ" target="_blank">https://youtu.be/KzYUzJPM3eQ</a></p>
<p class="ecxMsoNormal"> </p>
<p class="ecxMsoNormal">The purpose of this video is to demonstrate the importance
of riser height on the function of a natural draft, top-lit updraft gasifier
using the “Counter-Current Woodgas Burner” (CCWB).<span style=""> </span>Riser height affects the flow rate of both
primary and secondary air, and the degree of turbulent mixing of woodgas with
secondary air.<span style=""> </span>Increasing riser height creates
greater buoyancy forces that can improve the efficiency of stove combustion,
and stove responsiveness for the operator, but it can lead to excessive secondary
air, and excessive turbulence under some conditions.</p>
<p class="ecxMsoNormal"> </p>
<p class="ecxMsoNormal">With a true counter-current burner, the fuel gas and
oxidizer gas collide head-on.<span style=""> </span>This is
more-or-less what happens with the CCWB, because a downward laminar flow of
secondary air is sent against the upward flow of woodgas.<span style=""> </span>However, it is not a perfect counter-current
burner, because a lot of the secondary air is pulled sideways by the buoyancy
force created in the gas flame.</p>
<p class="ecxMsoNormal"> </p>
<p class="ecxMsoNormal">The main objective of the CCWB is to get a much turbulent
mixing of secondary air and woodgas at the base of the gas flame as
possible.<span style=""> </span>We are trying to approach an
ideal of a pre-mixed flame at somewhat above (to be determined) the
stoichiometric requirement for oxygen.</p>
<p class="ecxMsoNormal"> </p>
<p class="ecxMsoNormal">The second objective of the CCWB is to locate the base of the
flame over the fuel bed char.<span style=""> </span>Some
secondary air supports glowing char, and sustains a higher temperature in the
fuel bed, from the ignition front up to the top of the char, than would be
obtained if the secondary air and the gas flame were located at some distance
above the fuel bed.<span style=""> </span>Glowing char
can help with cracking of tars, and provide heat to assist in the piloting of gas
ignition.<span style=""> </span>This helps maintain woodgas
flame stability at low gasification rates.</p>
<p class="ecxMsoNormal"> </p>
<p class="ecxMsoNormal">Some modifications of the CCWB have been tried, but did not
show much benefit.<span style=""> </span>(1) A ring of small air
holes (of various numbers and diameters) in the sidewall of the reactor were
positioned just below the inner riser.<span style="">
</span>It was thought that these holes would provide small flamelets that would
keep the gas flame from extinguishing at very low gasification rates.<span style=""> </span>It was found that these holes didn’t help,
and functioned more to diminish the role of the counter-current air flow. (2)<span style=""> </span>Various fins were made at the bottom of the
internal riser to see if they would increase turbulence.<span style=""> </span>Fins were found to be unnecessary.</p>
<p class="ecxMsoNormal"> </p>
<p class="ecxMsoNormal">The stoves in this video are prototypes.<span style=""> </span>They are working hypotheses that need
scientific stove testing to optimize their geometry, and validate the
counter-current approach. To become working stoves, they need a regulator for
primary air, an insulated external riser, and mechanism to transfer the heat to
the pot or other object of work.</p><p class="ecxMsoNormal"><br></p>
<p class="ecxMsoNormal">If the CCWB can be shown to improve combustion efficiency on
diverse biomass fuels, and over a wide range of gasification rates, that would
be good, because it is a very easy burner to build.</p><p class="ecxMsoNormal"><br></p><p class="ecxMsoNormal">Cheers,</p><p class="ecxMsoNormal">Julien.<br></p>
<br clear="all"><br>-- <br><div class="ecxgmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr">Julien Winter<br>Cobourg, ON, CANADA<br></div></div></div></div></div></div>
</div>
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