<div><div>Crispin, those refractory tubes are " heat riser tubes" they are used on the openings to a sand mold to hold extra liquid metal. As the metal cools and contracts in the mold they allow extra metal to flow in so no air gaps appear in the casting. They have to hold heat longer than the mold so the metal in them is the last to solidify. - Dan Dimiduk. </div><div><br/></div><div><i><font style="color:#333333">Sent from my Verizon 4G LTE Droid</font></i></div></div><div class="elided-text">On Mar 17, 2019 6:52 PM, Crispin Pemberton-Pigott <crispinpigott@outlook.com> wrote:<br type='attribution'><blockquote class="quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<div style="width:100%">Dear Aaron</div>
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<div style="width:100%">First I must correct any impression about fuel chamber size. Read carefully, I think I didn't refer to the chamber holding the fuel. </div>
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<div style="width:100%">You can view the fuel chamber thus: the diameter gives an area which gives the power you want. The height of the chamber gives the burn duration. </div>
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<div style="width:100%">The actual numbers will change with the fuel but once you have the fuel selected and a power + duration for one set of dimensions, you can calculate the size you need. It is not quite
linear, because the outside of the fuel bulk will behave slightly differently from the middle. </div>
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<div style="width:100%">About your observation concerning the material finish when the stainless is reflective, it picks up the infrared radiation very poorly, reflecting it back into the gas stream. Once
it is tarnished, it absorbs far better. That raises the temperature of the shell and drops the combustion temperature quite a lot. </div>
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<div style="width:100%">This is a valuable lesson. If you have a ceramic liner (which doesn't have to be very insulating) it will get very hot and the surface, heated by the IR, will glow. This sends the
energy back to the gas and the other side, rinse, repeat. </div>
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<div style="width:100%">So having a reflective surface, or a glowing ceramic surface, or a glowing insulated surface, keeps the heat in. That in turn keeps the temperature up. Result: super-clean burn. If
you see no orange or yellow or red, there are essentially no particles. Just gases. </div>
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<div style="width:100%">Obviously if you have more air in there than you need, the temperature will drop, which is the same as the surface tarnishing. It is very likely that as you play with the amount of
secondary air, you will find the sweet spot. Once found it will be reproducible anytime you like (for that fuel and moisture). </div>
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<div style="width:100%">With no instrumentation at all, you can judge using you naked eyeballs in the exhaust stream well above the fire if there are more or fewer particles. First check for no smell.
Smell goes first. If no smell, then try your eyes. If no smell and nothing bothers your eyes, it is extremely clean. </div>
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<div style="width:100%">Even coal can be tested this way. Perfectly burned it doesn't smell of anything. Kerosene seems to have characteristic lingering odour. </div>
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<div style="width:100%">Your ND unit with the secondary chimney looks really close to optimal. Just play with the diameter and the secondary air volume. A vortex deliberately created is fine but requires
a much talked and smaller pipe. I have created vortices inside a 50mm pipe in which the flame persisted for more than 600mm. The cleanest result for CO was at a very low excess air level: 35%. This is possible because the turbulence was massive and the heat
loss from the pipe was quite low (stainless steel pipe). </div>
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<div style="width:100%">There are 4" diameter refractory tubes used I think by blacksmiths in the US. I have seen them advertised. Maybe they are for foundries. They make a perfect chimney to wrap with
sheet metal. Maybe try to find two. </div>
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<div style="width:100%">Lastly, something that can help keep the combustion temperature up is preheating the secondary air. There are multiple ways of doing that. In the KG4 stoves the air if pulled through
AA bed of red hot Cole getting a pre-heat of 800 C which really helps the CO burnout. You can't get that temperature with metal. It's kind of a cute trick. </div>
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<div style="width:100%">Regarding the fans: you can block the inlet of such a fan easily. The fan doesn't mind. It uses less power then partially blocked. Alternatively, vent some air to the side, or use
a controller of current or voltage. </div>
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<div style="width:100%">Regards </div>
<div style="width:100%">Crispin </div>
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<p dir="ltr">www.newdawnengineering.com</p>
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<div><b>From:</b> wingleaaron@gmail.com</div>
<div><b>Sent:</b> March 17, 2019 4:43 PM</div>
<div><b>To:</b> stoves@lists.bioenergylists.org</div>
<div><b>Reply to:</b> stoves@lists.bioenergylists.org</div>
<div><b>Subject:</b> Re: [Stoves] A Premix Burner</div>
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<div>Thank you Crispin, </div>
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<div> I’ll try out your suggestions of a smaller Secondary burn chamber diameter as well as reducing the diameter of the fuel chamber for efficiency. That forced air stove is the only time I have experimented with a fan and I appreciate the
review of the flames in the Multiple stoves. Unfortunately I scrapped that FA stove last time I became fed up with TLUD stoves so I cannot experiment with lesser fan speeds until I can afford to rebuild it. ($65) The fan used was definitely way too big and
that thing was scary hot. One interesting observation I found was that the nearly 100% invisible Flame phenomena seemed to happen only when using a new and shiny stainless steel stock pot in ND mode. Once the stainless finish dulled, the invisible effect
never came back. That could be an effect of radiation or a catalyst reaction from the stainless steel. With a 4” diameter secondary Combustion chamber and no external riser in place I have also gotten nearly invisible flames as well, but not to the same extreme.
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<div>As far as Paul’s Stove, which is way exciting to me, I love the design as it feels like a simple burner attached to a small disposable propane tank which I have used for many years of my life. I can’t see the flame really well, but it appears
to be using rice husks as fuel yet again but I would expect very good results for wood pellets and chips. I assume the forced air is only being used as primary air since there is a Secondary air Venturi injector just under the burner. If there is gas leakage
then too much primary air is being applied IMO. I’ve always shied away from FA TLUD but this stove makes a very strong argument for this design. I see no way to light this stove as a ND or at least it could be difficult but worth attempting. It looks simple
to use and I’m guessing it’s not finicky even for lighting. Thank you Paul, for sharing this design. </div>
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<div dir="ltr">On Sat, Mar 16, 2019 at 8:12 PM Crispin Pemberton-Pigott <<a href="mailto:crispinpigott@outlook.com">crispinpigott@outlook.com</a>> wrote:<br />
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<p>Dear Aaron<u></u><u></u></p>
<p><u></u> <u></u></p>
<p>Thank you for providing the video links and bringing your experiments to this discussion. There is always something to learn from these investigations.<u></u><u></u></p>
<p><u></u> <u></u></p>
<p>I am making some assumptions so please correct me if this is not the right sequence.
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<p><a href="https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2Fp_01Uy6sEl4&data=02%7C01%7C%7Cd0275137a97548fcb7c008d6ab19372c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636884522119552414&sdata=DDp1cgBvXeVZIngNzZP%2FAvNDiB3vWaf59%2FYqUu5jNic%3D&reserved=0">https://youtu.be/p_01Uy6sEl4</a><u></u><u></u></p>
<p>FA - Secondary Combustion Chamber <u></u><u></u></p>
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<p>The first video is the short, loud one “making char”. There is a lot of turbulence but still, it is possible to see some of the flame characteristics. The general appearance is that of translucence. This is a good sign of a clean burn.
The orange colour is caused by hot carbon particles with a short lifespan glowing as they evolve. The colour is from the glow of the particle, not the colour of the flame from combustion itself.<u></u><u></u></p>
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<p>At the top can be seem slightly orange flames coming out at high speed. These appear and disappear rapidly as they cook in the ambient air. A judge the flame to be extinguished by cooling before the gases have completed the burn. In that
case you can expect there is some particulate matter escaping before they finish oxidizing. In that case you will also have some CO. I would like to see the fan turned down then increased slowly to observe how that flame changes as the air supply is increased.
It is probably cleaner at lower fan speed. In general we can notice the flame is short of secondary air because it is still a diffusion flame as it hits the ambient air (still looking for oxygen).<u></u><u></u></p>
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<p><a href="https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2F25GRrEi9u74&data=02%7C01%7C%7Cd0275137a97548fcb7c008d6ab19372c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636884522119562425&sdata=eKNZsiXY1oKP5j9He6RYh4k%2F2mHhRZeaveaa826fZD0%3D&reserved=0">https://youtu.be/25GRrEi9u74</a><u></u><u></u></p>
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<p>ND-TLUD with Secondary Combustion Chamber<u></u><u></u></p>
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<p>>It’s been difficult to fully prevent backfiring if these stoves by sizing the openings properly but I do have at least 1 that works dependable. … The forced air version does not have backfire issues cause the primary burn chamber has
a bit of flame in it. <u></u><u></u></p>
<p><u></u> <u></u></p>
<p>There is an important difference between the oxy-acetylene flame and the producer gas flame which is the mixing ratio at which it will burn. Acetylene has a wide range over which it will burn and the flame varies. Producer gas is more
demanding about the air-fuel mix. “Natural gas has a very, very steep curve for flame speed. This is why the smallest primary air change makes so much difference in flame appearance.”<span style="font-family:'open sans' , serif;color:#3d3d3d">
<a href="https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fforum.heatinghelp.com%2Fdiscussion%2F86886%2Fflame-speed-question&data=02%7C01%7C%7Cd0275137a97548fcb7c008d6ab19372c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636884522119572430&sdata=ma486W8Aql2jQ0lI67izITPKC%2BfVs8iJ2cavx%2FYpSgE%3D&reserved=0">
Here</a>. </span>“Other factors affecting flame speed include the temp. of the fuel and primary air, burner temp., size/shape of burner or combustion c</p></div></div></div></div></blockquote></div></div></div></div></div></blockquote></div>