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Post by Jura on Oct 15, 2020 0:56:23 GMT -8
.... Not bad at all, good enough for the new norm and way better than the present. Ugh...That's a really huge piece of a good news. I can not wait to set up this core ...but still need Santa Clause to bring me a TESTO ;-) |
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fuegos
Full Member
not out of the woods yet
Posts: 177
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Post by fuegos on Oct 15, 2020 2:48:27 GMT -8
"This core seems to be suited best for a smaller cooking range or a mass-less heater, running less powerful but over a longer time span"
this is really exciting news for me. I live in a well insulated cabin 650 M up in the mountains & the wide range in outside temperatures means any system that stores heat could be very tricky to use.Last night was about 0 c the previous afternoon reached 22 & we woke up to the cabin at 17 c so a very small fire , literally a few sticks burned in the box stove quickly heated the space up to 21 c .I'm looking forwards to seeing the plans on the final build.Thanks to all involved for putting in the work and sharing.
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Post by satamax on Oct 16, 2020 23:55:42 GMT -8
I have a question about an aerodynamic aspect of venturi ports. All of those ports have been built as straight openings, the front is just as wide as the rear end. Imagine one would sculpt it a bit, one of the sides a little bit wider than the other. Which side would that be then, front facing the firebox or rear facing the afterburner? The ceiling of the firebox where the port is situated is CFB material so I could use a sharp knife to make it a bit wider on one side. Which side would be most likely to speed up the gas stream? Peter, if you want your turbulence to be still there. I would say front, front and front. Basically the port isn't a venturi per se, but a "sharp orifice" Remember this one? youtu.be/KS-GSLrkf30I think the depression on the back edge of the port is more important than the front overpressure. Here is what happens in the sharp orifice as we use it. I think.  The trailing edge of the port should not be touched, to allow for the maximum turbulence to be achieved behind the "wall" Underpressure create turbulence in that case. I think. |
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Post by satamax on Oct 17, 2020 0:06:26 GMT -8
I would shape the leading edge as a very flat rounded funnel. Keeping at least 2/3rds of the usual 5 cm brick thickness. So the path of gases on the side with red lines, would crash into the edge of the other side of the port. Increasing turbulence. If you see what i mean.
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Post by Karl L on Oct 17, 2020 0:13:35 GMT -8
One thing to suggest Max is right is the Coanda effect.
I think that if you widen the exit side of the port then the Coanda effect will cause the 'jet' of gasses to widen, because will 'stick' to the port walls. If you narrow the port exit then the opposite might occur.
I am guessing that the wider jet won't form the rams horn vortices so well as a narrow jet.
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Post by satamax on Oct 17, 2020 0:18:33 GMT -8
One thing to suggest Max is right is the Coanda effect. I think that if you widen the exit side of the port then the Coanda effect will cause the 'jet' of gasses to widen, because will 'stick' to the port walls. If you narrow the port exit then the opposite might occur. I am guessing that the wider jet won't form the rams horn vortices so well as a narrow jet. Mitigated by the laminar flow deceleration if the port is too small. |
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furno
New Member
Posts: 23
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Post by furno on Oct 17, 2020 2:18:22 GMT -8
I would shape the leading edge as a very flat rounded funnel. Keeping at least 2/3rds of the usual 5 cm brick thickness. So the path of gases on the side with red lines, would crash into the edge of the other side of the port. Increasing turbulence. If you see what i mean. This design is actually used in some gas burners. A vortex forms behind the sharp edge of the port, which ignites the mixture immediately after the port. If you look at the port after a fire, soot burns out behind the edge of the port. This indicates a local high temperature. I made such a port in my firebox.  [rus] Такая конструкция действительно используется в некоторых газовых горелках. За острым срезом порта образуется вихрь, котрый поджигает смесь сразу за портом. Если посмотреть на порт после пожара, то за кромкой порта сажа выгорает Это говорит о локальной высокой температуре. Я сделал в своей топке такой порт. |
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Post by peterberg on Oct 17, 2020 6:34:04 GMT -8
satamax, fact is that I've built it up in bits and pieces, no large enough pieces anymore. Just right after I chamfered the front end only, flames entered the port from below visably quicker and the stream seemed to be wider as well. Which could mean the current port need to be narrower on top, instead of wider on the firebox side.
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Post by peterberg on Oct 18, 2020 8:16:17 GMT -8
Hmmm... I've got a mail to call in my Testo for recalibration. Most of the time this will take a couple of weeks before I'll have it returned. I think I'll try to hack into the core as it is in order to implement the port with slightly slanted sides in the coming days. And run a couple of tests using that configuration.
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Post by peterberg on Oct 19, 2020 7:59:57 GMT -8
The diagram below is of October 15th, nothing has been changed as compared to the one prior of that date. Except, the fuel was more tightly packed, also at the lowest level.  It came on very quick which is a good thing because the earlier the vortexes are spinning the cleaner the burn will be. That is to say, that is the intention. But somewhere halfway in the burn it took a wrong turn: it slowed down, the afterburner switched off and the CO line started to rise. Air visably couldn't reach the bigger pieces at the bottom, it burned only at the front end. That's a difference with the bog standard batchrocket which is sporting a much more pronounced cross draft. This happened to be not a good burn, sub-optimal at the very least. So I took some mental distance from these results and try to come to a decision what to do next. I didn't put the knife to the port just yet. The question that needs to be answered first: is this the direction I want this core to go? To some people, even the precise measurements of the port in any batchrocket is already complicated. Let alone a configuration that is leaning on precise angles and different dimensions of the port's leading and trailing edges. Before I do something drastic, I'll contemplate about it. Today I opened the bottom slit of the air frame a bit more and taped a bit more of the side slits. Two moderately large pieces at the bottom, lots of space around and between. Three pieces of the same size above that, thinner pieces next and kindling on top.  This happened to be more like it: it came on quick again but ran much more agressive. The O² line took a deep dive twice but the CO line barely reacted to these events. Average numbers: 12.2% O², 94.4% eff., 666 ppm CO, 76.8 ºC. Corrected for an O² level of 13% the CO average would be 625 ppm, less than half the level for the coming EU norm. Having more low front air and space around the pieces at the bottom seemed to help. For now, I postpone the different port implementation and try to find the solution in tuning the air supply. |
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Post by Vortex on Oct 19, 2020 8:40:13 GMT -8
Interesting how the O² dropped below 6% and the CO never even flinched, always goes vertical below 8% on mine. Your later air arrangement is closer to my setup, which has 10% air at the bottom and the other 10% fairly equally spread around all 4 sides. What's the threshold like you are using? I get best results with it between the full height and half height of the primary air inlet, higher seem to result in more CO. The lower air position probably compensates for the reduced cross flow.
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Post by peterberg on Oct 19, 2020 12:33:17 GMT -8
@trevor, my air setup doesn't use a threshold as such. All air is coming through the air frame after all. Before I start a new test I'll try to make some pictures of the diverse ways how air is coming in. My thought also, about the lower air position might compensate for the lack of cross flow.
So the CO level in your heater core goes haywire when O² drops below 8%. I was expecting exactly that when the O² dipped down to 5.8% and 5.5% within ten minutes. But it didn't much to my surprise, now I have to find out whether or not this behaviour is repeatable. During both those low points the vortexes were looking quite violent. Two maelstroms moving in the direction of the glass in short bursts, seemingly out of sync with each other.
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Post by Vortex on Oct 20, 2020 3:22:08 GMT -8
Only way I'd get the O2 that low is if there was an air leak somewhere in the mass, so hopefully you've discovered something new. The flow of gas in the port is very laminar, it tends to stay on the side of the firebox that it originated from, so you'll notice that quite often one side the vortex will be more pronounced than the other. Very occasionally you'll get a rich stream of wood-gas right in the middle of the firebox below the port, and it'll flip back and forth from one side to the other giving that pulsing side to side effect. Best video I think I have of that is an old one from my early experiments outside: vftshop.com/Video/williecoyote.mp4 |
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Post by satamax on Oct 20, 2020 3:54:20 GMT -8
satamax, fact is that I've built it up in bits and pieces, no large enough pieces anymore. Just right after I chamfered the front end only, flames entered the port from below visably quicker and the stream seemed to be wider as well. Which could mean the current port need to be narrower on top, instead of wider on the firebox side. Peter, My view, on the subject. Is, even if the port is funneled, or rounded in front, what happens, is you have a bigger surface area at the front, then the gases taken at that point get accelerated, when the "venturi" is narrowing. Like if you were blowing in reverse, in a trumpet bell front end. Or a funnel. Why i was advocating for a rounded profile, instead of funneled, is that the change of direction of the gases stream is always changing during it's progression against the port's sides. Thus, may be increasing the turbulence. Instead of a funnel shape. But not having those flow visualisation videos of funnels etc on youtube, means i can't verify my gut feeling. What i picture in my head, is gases led to crash into the opposite side of the port's edge. Increasing the turbulence on the "sharp orifice" rear end of the port. I have found some of those again. |
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Post by Vortex on Oct 20, 2020 6:28:00 GMT -8
This one was interesting. Laminar vs Turbulent flow:
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