Actually, this thread started somewhere in the large Vortex thread. Here's a link to those posts. donkey32.proboards.com/post/34900/thread Trevor placed a link back to this thread at the page where the last relevant post is.
OK, yesterday I did two burns, more or less in succession. The first one started from cold looked quite good. A full load of willow branches, moisture content 12%. Lit on top with a handful of small pieces very dry pine.
The top box doesn't look much different, just that it's done in CFB with a shelf out of cast refractory. The exit port is not on the shelf but in the ceiling right against the rear wall. It seems the afterburner space in Trevor's drawings is twice as wide as it's high. The lower part of the top box is 180 mm wide and 90 mm high. The space above the shelf should be 218 mm wide and 58 mm high. I couldn't realize that in the confined space, so it's 180x70 mm which is the same csa-wise. In this implementation the size of the exit port is 180x32 mm. All still within reasonable tolerances, I'd say.
It came on very slow again but once the O² dropped below 20% it became progressively more fierce. The video below is around the full burn.
My Testo threw up an old problem: the temperature reading didn't work well, it went up and down and too low. As a consequence, efficiency numbers are foolishly high. But here's the diagram.
Averages of this burn: 11.8 % O², 666 ppm CO. Not bad for a first iteration, not bad at all. It ran without a hitch using the DSR2's air frame, without the floor channel of course.
Last Edit: Apr 12, 2021 8:01:20 GMT -8 by peterberg
Peter, if I may ask a question about your motivation, what is it about the Vortex design elements that interests you? Are you trying it to verify the design parameters in a different configuration, or do you perhaps see some beneficial features compared to the DSR2?
I'm not trying to judge any better or worse, just comparing and contrasting to better my understanding. It looks like the Vortex saves on depth of design by stacking the afterburner on top, and the flaming vortex sure looks amazing! Perhaps the port over the firebox also has benefits of flames and gas following a natural upward path.
Peter, if I may ask a question about your motivation, what is it about the Vortex design elements that interests you? Are you trying it to verify the design parameters in a different configuration, or do you perhaps see some beneficial features compared to the DSR2?
The Vortex core is painfully slow (in my setup) to start the afterburner flame as compared to the regular batchrocket and DSR2, so that's a negative point. On the plus side, the view of the double vortex is spectacular, lots of people would like that. Both DSR2 and Vortex are able to run quite long on one single batch and aren't prone to overfuelling due to the restricted end port. Since the DSR1/Vortex port is in the ceiling, it's virtually impossible to block it or stick something in it. This aspect means it is more fool proof. And last but not least: the Vortex core is much shorter in depth. It would be nice to find ways to speed up the cold start. Most of my experiments are driven by curiousity and since I am retired I have lots of time on my hands. Time is money, all time is mine so I am very rich.
Perhaps the port over the firebox also has benefits of flames and gas following a natural upward path.
Yes and no, yes there's less chance of smoke coming out of the front when the door is open. And no, the double vortex in a regular batchrocket can be formed within 3 minutes despite the fact it is a horizontal path.
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?
Last Edit: Oct 7, 2020 11:35:26 GMT -8 by peterberg
Peter, if I may ask a question about your motivation, what is it about the Vortex design elements that interests you? Are you trying it to verify the design parameters in a different configuration, or do you perhaps see some beneficial features compared to the DSR2?
The Vortex core is painfully slow (in my setup) to start the afterburner flame as compared to the regular batchrocket and DSR2, so that's a negative point. On the plus side, the view of the double vortex is spectacular, lots of people would like that. Both DSR2 and Vortex are able to run quite long on one single batch and aren't prone to overfuelling due to the restricted end port. Since the DSR1/Vortex port is in the ceiling, it's virtually impossible to block it or stick something in it. This aspect means it is more fool proof. And last but not least: the Vortex core is much shorter in depth. It would be nice to find ways to speed up the cold start. Most of my experiments are driven by curiousity and since I am retired I have lots of time on my hands. Time is money, all time is mine so I am very rich.
Perhaps the port over the firebox also has benefits of flames and gas following a natural upward path.
Yes and no, yes there's less chance of smoke coming out of the front when the door is open. And no, the double vortex in a regular batchrocket can be formed within 3 minutes despite the fact it is a horizontal path.
Peter, The slow start you are seeing in your setup does not normally happen in my 6" or 4" Vortex core, so there must be some difference that is causing that. It can be caused by too slow a fire, too much air, fire too far from port, too strong a draft, or a cold afterburner, so you should be able to solve that issue.
Today I fired it again to show it to a friend of me. Didn't have the Testo meauring it, I'm contemplating what to try next.
#1 slow start, yes #2 too much air, not likely #3 fire too far from the port, no #4 too strong draft, the draft limiter took care of that $5 cold afterburner, yes totally
It started quicker now, less logs (2.5 kg) and more kindling. Ram's horns running for approx. an hour uninterrupted. That leaves the cold afterburner as the main cause.
Next experiment: placing an object on the shelf and maybe at the ceiling as a stumbling block. If and when that seems to work opening up the exit port a bit at the time. Separate from that, shifting the shelf a bit forward, maybe that is on top of the list. All this will take some time, my workshop will get too hot in the situation of doing one run every day. Unless it starts freezing within a week but that would be very, very, very unlikely.
I forgot to say, the other thing I would try is making the exit port larger. Just as none or too big an exit port leads to overfuelling, to small an exit port makes it run slow - underfuel. The size seems to be determined by the strength of the draft of the chimney and mass.
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?
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?
Direct link: www.cell.com/heliyon/fulltext/S2405-8440(18)37416-4 As far as I can tell all these nozzles are round instead of rectangular. And there is not as much space after the venturi in our afterburner I think.
Direct link: www.cell.com/heliyon/fulltext/S2405-8440(18)37416-4 As far as I can tell all these nozzles are round instead of rectangular. And there is not as much space after the venturi in our afterburner I think.
yes and yes, shapes do differ and so do spaces, but:
1 - isn't it possible that some similarity still exists, no matter of port shape? with some approximation at least?
2 - they say in the article that "The length of the nozzle did not have as much of an effect on the performance as the shape of the nozzle right before and after the throat" - so the afterburner's inner space shouldn't matter very much, no?
I forgot to say, the other thing I would try is making the exit port larger. Just as none or too big an exit port leads to overfuelling, to small an exit port makes it run slow - underfuel. The size seems to be determined by the strength of the draft of the chimney and mass.
You named the space above the triangular ridge on top of the shelf as the exit port. While I'm calling the exhaust opening out of the core into the bell by that same name. To add to the confusion: the side opening (to your oven?) you are naming the exit is also a restriction since it isn't as large as the chimney, csa-wise. According to your drawings and assuming your chimney is 150 mm in diameter.
What I built just now doesn't sport your exit port, the exit (or exhaust) is the only restriction (105% of port size) and is on top at the far back. No overfuelling uptil now when started cold so it works as planned. What I am planning to test next is making the bell a bit smaller so chimney temperatures would be higher. Cutting the top barrel 25 cm shorter might be cancelling the slow start. A ridge on the shelf like the Vortex core or ceiling like the DSR2 is also on my list. In combination with a widened exhaust port/opening at the top as an option.
I showed the experimental core to a friend yesterday. It happened to be a windy day, accompanied by strong gusts. My house is not ideally situated with an appartment block near by, so sometimes a gust of wind can be blown into the chimney. The small core behaved similar to the DSR2 in that respect: the flames of the vortex became subdued for a moment and stretched out all the way to the exhaust end. Suddenly stronger draft caused the opposite effect, the vortex became brighter and more compact, no flames at all over the shelf. This behaviour is counter-intuitive I would say, have you experienced similar behaviour Trevor?
Last Edit: Oct 9, 2020 8:03:23 GMT -8 by peterberg
I have an anti down draft chimney cap and a draft regulator set to it's most sensitive setting, so I now only get that behavior when it is very strong gusty winds, but it happened a lot before as I'm right on the edge of the Atlantic ocean where it's very windy.
It does seem counter intuitive, but I believe it forms a brighter more compact vortex because the sudden increase in draft is translated into faster spin of the vortex. Whereas the blowback stall causes a slower gas stream which doesn't have the energy to spin the vortex up, so it moves straight through the afterburner and into the top chamber with very little spin. Does that make sense?
Apologies for the naming confusion. My original exit port (that I've later referred to as the exit) is an integral part of the stove design and difficult for me to remove completely, so when I wanted to move the position of the exit port I set it to the maximum size and made another one on top of the afterburner shelf with the triangular piece, so I tend to forget the original's still there. The important thing seems to be the amount of resistance to gas flow in the system, (as you saw from the gusty wind, an increase or decrease makes a big difference) There seems to be a relationship between the strength of the draft and the exit port size. I moved the exit port closer to the afterburner because that seems to keep the flame in the afterburner better and so gave lower carbon monoxide.
The port is basically a laminar nozzle (like on a fountain), most of the mixing being done by the turbulence of the vortex. I've thought about trying out a port that was wider at one end. As I understand it the width of the port relative to the afterburner chamber determines the spin of the vortex. Too narrow and there isn't enough wood-gas to produce a vortex in the afterburner - too wide and there isn't enough room to produce the vortex. So I think a slight difference in width would produce a vortex with slightly more spin on one end than the other. An extreme example can be seen in my test of a round shaped port (where the middle is very wide and the ends are very narrow), the vortex forms points in the middle:
My Testo threw up an old problem: the temperature reading didn't work well, it went up and down and too low. As a consequence, efficiency numbers are foolishly high. But here's the diagram.
I had the same issue with my new testo. I tried all sorts to figure out what was causing it; cleaned all the contacts between the thermocouple and the probe, old probe on new testo, new probe on old testo, etc. What finally fixed it was, putting the thermocouple from inside that useless probe that comes with the solid-fuel adapter kit, into the normal probe from my new testo, hasn't done it since. Hopefully that's some help.
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Donkey: rockinon, place them on some other web hosting service and link them here.
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atrii: How can I see these photos Donkey?
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Donkey: atrii When the images are properly linked, they will be visible.
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dvawolk: For images i use "Greenshot" app - i can print screen part or whole of my screen and upload them directly to imgur throught the context menu. Works very well and fast for me...
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lightworker: Hi beppe:
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