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Post by DCish on Jan 1, 2019 10:04:52 GMT -8
Whew. I continue to be only able to experiment in fits and spurts, and every time I come back to it, there has been so much development that my own ideas of what I want to try have to catch up! My next core idea picks up from where I left off with my Walker Core Variation and builds on it with inspiration from Peter's Double Shoebox (DSR) and Vortex's " Ancient Aryan" style afterburner. My goal is still to get to a design that I am comfortable bringing in the house to feed the dead-end bell bench that I already built. I'm opening this thread now despite having not started testing things yet, because I have fallen into discussing aspects of it with Trevor on his Vortex stove page, and didn't want to get too off-topic from what he is doing there. If all goes well, I'll have something to show in the course of the next few weeks. The basic idea is a standard batch box, but side loaded, and with a slot in the top facing away from the "front" such that the Vortex is visible as gases flow away from the front, do a 180* turn, come back toward the front, then exit to the right to flow into the bench. Should be fun... |
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Post by Vortex on Jan 1, 2019 16:06:12 GMT -8
Well done Brian, I look forward to following your progress  imgur.com is one of the best free image hosting sites now, and I like Vimeo for video hosting: vimeo.comEDIT: Vimeo is now a scam - avoid. The only benefit of having the flame come towards the glass I can see is it quickly burns off any smoke residue from the startup phase, but the downside is it seems to gradually etch the surface of the glass and makes it slightly opaque. So will be interesting to see what difference that makes to yours. I have definitely noticed the soot accumulation during startup. I have toyed with the idea of adding an air wash as is generally done with stove door glass, which could possibly be the source of secondary air, now that I think about it, since for me my glass will be before the slot, not after it. But that is for a later phase when I get to working on doors. Also, my current plan, based in part on the space constraints, is to have a bypass that exits out of the back of the firebox itself, but I would also hope that it would minimize the initial afterburner window soot accumulation problem. I am also hoping that by having the vortex directed away from the glass it might stay cooler and minimize etching over time. An airwash secondary air setup sounds like it might be a good idea for the design you have in mind. Though I found in my experiments alot of secondary air from the rear of the port seemed to push the jet of flame forward, and impede the formation of the double vortex. I tried a lot of different ways of injecting heated secondary air, and found that the stove burned just as well without any, but that could be because my firebox is a lot shorter, and a lot of primary air seems to go straight up over the fire and up out through the port. Best secondary air position I found in my arrangement was a small amount in from either side at the front inside edges of the port, which produced a good double vortex with nicely defined spirals. I'm not sure about a bypass straight out the back of the firebox. I find the hotter the afterburner the better it runs. Think of it like priming an old kerosene pressure stove. When you shut your damper you'd be subjecting the cold afterburner glass to sudden intense heat, which could theoretically cause as much damage from the thermal shock, than as if it was in the flame path the whole time, as then at least the heat gradually increases. |
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Post by DCish on Jan 1, 2019 19:18:29 GMT -8
imgur.com is one of the best free image hosting sites now, and I like Vimeo for video hosting: vimeo.com Thanks for the tips, I'll check them out. Played a bit tonight (post to come)... I see what you mean. I think I have some experimenting to do before I'll have it right. Good point. It has to heat up sometime. I may be just as well off being sure that I put enough small stuff in so that it gets good and bright good and quick, and let everything come up to temp together. My flu path should allow a bypass in a similar position to yours, so that should work just fine. We'll see how things develop. |
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Post by DCish on Jan 2, 2019 13:05:59 GMT -8
Found a round tuit on New Year's day, so I built and tested a prototype. Here's what it looked like...       Nice fire fountain right from the outset  1) This video is from immediately after lighting. Bamboo kindling w. ~1" Oak splits. Quick fire fountain despite wet brick that has been sitting out in the rain. Sides and bottom of afterburner are insulating firebrick. Burn box sides are of dense firebrick. 2) Heating up / soot forming. Clearly the slot is a bit off center, the left vortex being more open than the one on the right. I can't decide which I like better. 3) More soot accumulation despite strong burn. I'm thinking this has something to do with how cold and wet the bricks were at the start, but can't say for sure. 4) Coming up to temp, fire waning, but window clearing 5) High burn. I think I added some more fuel here, and I think this is where I started playing with the air a bit. By now the bricks are probably dry in high heat areas. And the second window on the right is starting to clear of soot. Note how, typical of high burn events, the flame front moves further down the afterburner channel. 6) Top of burn. Much of the afterburner chamber is glowing red, though it is difficult to make out in the video. Flames are taking on that light blueish, reddish, translucent look that seems to be associated with high afterburner temps. Soot continuing to burn off. 7) I think this is where I begin tweaking the secondary air. Before this, the secondary air flap was closed almost entirely, and a 2" x 2" opening in the top right of the firebox let in secondary air (the top left of what would be the "door" on a standard batch box). 8) More secondary air fiddling. Flipping secondary air flap open and closed. With full open, the initial vortex disappears and the flame front gets pushed way down the afterburner channel. Outdoor temps are around 40*F, so... that's how it behaves without preheated air... 9) Primary air fiddling. Dedicated primary air slot was roughly 1/2" wide by 4" tall, in addition to numerous cracks in the dry stacked bricks. I had tuned secondary air to about 1/4" x 2" at the slot under the glass by that time, and it seemed to hold up well when changes were made to primary air flow. Not that these dimensions mean anything in relation to a standard, since there are so many cracks in the walls... 10) Larger Log re-fuel. After flames died down to just coals, I added a larger log (4" x 5" split). It coasted along like this for a long time (I went in for dinner and checked later and it was still doing this, more or less). The window didn't soot back up at all, and neither did the afterburner chamber. For as long as flame continued to pass through the port, the points of flame contact continued to glow faintly red (though that's hard to see in this video), indicating that temps remained fairly high, and exhaust gasses were invisible and odorless. This is the sort of burn condition that makes me wonder if perhaps a tighter afterburner chamber after the slot would be desirable. I wonder if perhaps the less space the flame has to keep heated, the longer high temps can be maintained throughout the burn. Makes me wish I had a flu gas analyzer... Morning after pics: Whole stove view  Inside the main burn box. Note that only the dark black by the entrance is from last night's burn. The majority of the rest of the discoloration is from other uses of the bricks...  View of primary afterburner and secondary afterburner windows. I suspect that the secondary glass collected more ash because it was out of the main gas flow - the chimney pulls flu gases up a brick before the glass. However, I find it interesting that, even so, there was enough heat to burn off much of the soot that had accumulated during the initial burn. Still a toasty part of the burn path. As I look at this pic, I'm tempted to do another burn with this same setup, only with 1/16" to 1/8" gaps at the left and right sides of the primary afterburner window. Might be a way to test the air-wash-as-secondary-air idea.  Slot and main afterburner chamber. No soot, but a significant amount of ash plastered to the roof above the slot!  Return path of afterburner. Discovered that there was a 1" x 3" gap in the back of the stove the entire time due to sloppy brick stacking! Er, tertiary air anyone?  Ok, that should do it. Whew, takes twice as long to write it all up than it does to actually do it! |
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Post by DCish on Jan 2, 2019 21:28:20 GMT -8
Just finished editing my last post to include pics and vids from last night's burn. Enjoy! |
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Post by Dan (Upstate NY, USA) on Jan 3, 2019 0:28:01 GMT -8
Cool, I like seeing the soot in video 7 (due to probably wood shifting) in the second window accumulate on the glass and then burn off.
If you had a Testo on it that probably would have been a CO spike.
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Post by Vortex on Jan 3, 2019 8:18:56 GMT -8
Wow, Brian you've been busy! Well done. It'll take a few fires to properly dry out all those bricks, it'll dampen the efficiency and cause some more sooting up of your glass till then, so all considered that looks really promising. I recommend sealing up the cracks in your bricks a bit better, and getting a piece of corrugated metal sheet to put over the top when your not using it, I found that kept it nice and dry once the bricks had dried out: www.vftshop.com/images/others/Stove/vsaab1.jpgThe opening on your switchback from the primary to secondary top chamber is about 116% CSA. With no mass and just a straight up chimney I found it needed a restriction there to create some back pressure, somewhere between 75-90% CSA. That really helped keep the double vortex in the afterburner. Even with a huge mass on it and a tight 180 degree turn out of the afterburner, I still only have a 1 CSA gap there. Your primary top chamber looks slightly too narrow, and as you said it's a little off centre. Also having the switchback so close to the end of the port makes it tug at one side of the double vortex distorting it. That's what led me to change to an up-and-over switchback instead of a sideways one. You can see it in my video from when I tried a side exit (the chamber was a bit to high as well so that didn't help): vimeo.com/309312491The flyash on the ceiling is normal. At first I thought my CFB was bulging down, but it was just an accumulation of ash stuck to the roof. It never seems to get more than about 1/8 inch thick before it falls off in bits. The flyash cleans off the glass easy enough, I use a baby-wipe every couple of days. When the flames are streaming around into the secondary top chamber, try giving it a bit more primary air. I find that the more restricted the primary air is the farther the flames travel out of the afterburner, (except in the coaling phase). And too much primary air causes the vortex to just form a T shape above the port without the spirals. |
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Post by satamax on Jan 3, 2019 22:47:33 GMT -8
Note how, typical of high burn events, the flame front moves further down the afterburner channel. Nice looking rig. In my idea, a second venturi before the second afterburner chamber could be a good idea. Mind you, i understand fuck all to DSR  The flame front going further away from the port, i think, is because the draft is soo strong that it pulls it away. |
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Post by peterberg on Jan 4, 2019 1:56:53 GMT -8
To me, the most interesting aspect is the port orientation relative to the firebox. The double vortex can be established in almost any direction, we know that already. The crux of the thing seems to be the direction of the port relative to the afterburn channel/tunnel/riser or whatever.
May I remind you of the fact that my measured experiments showed a smaller channel didn't necessary burn cleaner? Rather the contrary, even a flat and wide channel where the double vortex made a fine show wasn't very good at that. Having it as a square cross section and larger than the expected system size, coupled with a secondary air provision in the far end of the port itself yielded the best results. I tried the front end and the top box as well to feed the secondary air in but it didn't cut the cake.
Some core concepts seems to be better in combusting black soot than others. And vice versa, when CO was brought to a minimum the exhaust could be smelled. Just now and then the configuration was in such a balance all carbon residue was combusted. Reaching this stage means the produced heat markedly increased for the same amount of fuel. Trevor have experienced this as well I believe, his iteration of the double shoebox could achieve even better results to my opinion. No gas analizer means you are going by eye, ear and nose only which is often wrong as I experienced quite some years ago.
Your port seems to be quite large, is it about 60% of chimney size?
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graham
Junior Member
Posts: 74
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Post by graham on Jan 4, 2019 13:38:49 GMT -8
What exactly is the definition for the ancient Aryan afterburner?
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Post by Vortex on Jan 5, 2019 2:47:31 GMT -8
docbb posted this in 2013 donkey32.proboards.com/thread/815/ancient-stoves?page=1&scrollTo=7405 it inspired me to want to try a port in the top rear of my vortex firebox. In respect to the original builder who called his video "Furnace of the Ancient Aryan's" I used the name Aryan Afterburner for the insulated top chamber. Basically it's a port in the ceiling into a heavily insulated chamber designed to spin the gasses up into a double vortex with as much of the 3 T's as possible.
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Post by DCish on Jan 5, 2019 8:24:03 GMT -8
The opening on your switchback from the primary to secondary top chamber is about 116% CSA. With no mass and just a straight up chimney I found it needed a restriction there to create some back pressure, somewhere between 75-90% CSA. That really helped keep the double vortex in the afterburner. Even with a huge mass on it and a tight 180 degree turn out of the afterburner, I still only have a 1 CSA gap there. I recall seeing this in your thread. I'm starting a list of things to alter in future runs, I'll add this in. I was already planning on playing with port width, but I may have to add the "up and over" transition as a something to play with as well. This is interesting, I'll play with these a bit and see what I see. Many thanks for your thoughts! |
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Post by DCish on Jan 5, 2019 8:39:59 GMT -8
Nice looking rig. In my idea, a second venturi before the second afterburner chamber could be a good idea. I'll add this to my list of things to play with, could be interesting to see what it does. Vortex already noted 75-90% restriction as being helpful, but I wonder what a "port" shape might do as far as flame shaping in the return segment This is one of the more curious things I have observed in various configurations. In video 8 there is a strong vortex until I open the secondary air which blows straight into the end of the port. After that there are still flames entering the port, but then the primary afterburner area is often empty of flame, which re-ignites later at the next 90* turn. In this particular case I suspect it has something to do with the fact that the cold secondary air puts out the flame until it mixes in and comes up to temp, then reignites because the burn chamber has retained enough heat. However, I seem to recall having had this happen at times when I wasn't introducing cold secondary air, so I don't know if there might be something else going on at other times. |
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Post by DCish on Jan 5, 2019 10:44:37 GMT -8
To me, the most interesting aspect is the port orientation relative to the firebox. The double vortex can be established in almost any direction, we know that already. The crux of the thing seems to be the direction of the port relative to the afterburn channel/tunnel/riser or whatever. Yes, that sounds about right to me. Yes, I do recall your writeup of this, and I don't doubt your data. I guess I am wondering about how things are taking place at various parts of the burn that ultimately accumulate into the final data picture. Your cores are optimized for quick, straight burns. One of the things that drew me to the Walker core is that he likes to keep the burn going for longer periods. His flame path immediately after the wood gasifier box (or whatever that should properly be called) is relatively narrow and relatively long, with a 90* turn in it, followed by some other turbulence-inducing elements, and he reports good testo results. This is where I got the idea that a tighter space immediately following the wood box may contribute to keeping temps up under lower burn conditions, and thus contribute to cleaner burn at various burn levels. In your cores, low burn conditions are a relatively small portion of the total picture, so optimizing for that wouldn't make much difference, and if changing one element to help at lower burn levels ends up messing up the balance required for high burn efficiency, it would ruin the total picture and be useless. Something else I am excited about from your exploration of the DSR is that it showed that the vortex itself isn't some sort of holy grail -- that its presence in the standard batch box does not "cause" complete combustion, it is simply the byproduct of a series of elements that, taken together, result in reliably good combustion. This leads me to think that it may be possible to set up a fire path that is aesthetically pleasing, and to play with any of a number of elements and ultimately arrive at something that fits certain space constraints, is aesthetically pleasing, and still gives good efficiency numbers. Trevor's experimentation with a slight restriction immediately after the initial afterburner area seems to have encouraging results in this direction. Fascinating. I am curious about the conditions where CO was minimal but exhaust smell was present. I am guessing from my own experience that a good hot burn, even with an over-abundance of air, would be how soot is combusted, but I'm not so clear on the conditions that result in low CO. Perhaps it would be that same hot burn, but with secondary air cut to the point that it began to pick up some odor (meaning that particulate matter is increased)? Yes, I am all too aware of the limitations of the human senses! Trevor, do you have a gas analyzer? If not, how did you go about tuning your stove? That the vortex-inducing DSR design you implemented reduced your fuel consumption so significantly means you got something right somehow... Yes, I originally had an "L"-shaped piece of insulating firebrick that I had used to form the port, but it broke while I was assembling things this time around. I decided to leave the broken bit out to play with how it behaves with cold, direct-into-port secondary air. The width is 2" and length was 8.75" for a total of 17 cubic inches, so your estimate is dead on at 60%. I plan to wedge that 2" chunk back in during the next run and see how that changes things. |
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Post by Vortex on Jan 5, 2019 12:19:11 GMT -8
Trevor, do you have a gas analyzer? If not, how did you go about tuning your stove? That the vortex-inducing DSR design you implemented reduced your fuel consumption so significantly means you got something right somehow... No I don't, I use the afterburner window and heat output. Being able to see the secondary combustion happening really helps me see what's going on and how any changes affect it. I'm actually more interested in the ascetics of a beautiful fire experience than getting the last few extra percent efficiency. |
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