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Post by drooster on Jan 5, 2019 14:04:32 GMT -8
... 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. Regarding the entry of secondary air into the port, could it be that the air has more of the ram's-horns to mix into being placed at the end of the port opposite to the exhaust? If so why does the normal batchbox not work better if secondary air is entered at the base of the port? (rather than middleish or top) Maybe the answer is in having no interference from the stack of wood? Just wondering the whys. |
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Post by Vortex on Jan 5, 2019 15:12:21 GMT -8
I was surprised how much the burning gases shied away from the heated secondary air. Maybe in a BB heatriser the heavier denser secondary air would sit at the bottom of the riser. Better to introduce it on top of the lighter burning gasses, then they're forced to mix.
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Post by peterberg on Jan 6, 2019 1:48:27 GMT -8
Regarding the entry of secondary air into the port, could it be that the air has more of the ram's-horns to mix into being placed at the end of the port opposite to the exhaust? If so why does the normal batchbox not work better if secondary air is entered at the base of the port? (rather than middleish or top) Maybe the answer is in having no interference from the stack of wood? Just wondering the whys. For a large part, the why's aren't as obvious. Experience is won by experiments and failures, theory comes later. First and foremost, the secondary air need to be heated up and injected in the area where the gases are speeded up because of the venturi. In a batch box that would be just before and sometimes in the port. Air injection in the riser itself has been tried by quite some people including myself but this didn't enhance combustion, rather the contrary. As it happens, I tried to inject air at the base of the port because it's the easiest but that didn't work at all. Next I made a couple of different systems that add air over the entire height of the port and that didn't satisfy me either. All done during the development of the floor p-channel. At some point I tried a vertical part only open at the top which worked better. Then I worked my way down to find out the shortest possible upright part and ended with the floor channel reaching halfway up the port. Conclusion would be that the top half of the port is the best location to add secondary air, as long it is hot. Cold air would cool the fire down, hampering combustion. That top half idea is also confirmed by Adiel Shnior in Israel, he had a heater core officially tested recently with very, very good results. His configuration sported a slit left and right inside the depth of the port in the top half. His air system is wide and spacious, air is heated up before it reaches the slits. In the slits itself velocity goes up due to the underpressure in the port so air is injected at speed although quite sparingly. Stacked fuel should allow some space in front of the port so air flow isn't hampered. Not much, 1/2" in a 6" system is enough. |
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Post by DCish on Jan 9, 2019 18:50:27 GMT -8
Two burns since last post.
Burn 1:
- Secondary air delivered via "air wash" in the form of a quarter inch gap on each side of the glass. Ultimately I tipped the glass in at the bottom to cut the flow in half with no apparent adverse impact on the burn. The flames didn't run away from the incoming air, but swirled around right up against the glass, so that seems to have potential as an air delivery point, though it would need to be pre-heated, of course.
- Restricted transition from 4.5" x 7" (86% of 6x6 square) to 4.5" x 5" (62% of 6x6 square, 80% of 6" round). This seemed to effectively encourage the burn to fill the primary afterburner area without choking it down - there was no pulsing at any point in the burn, even with an aggressive refuelling.
Burn 2:
- Added 2" upright secondary air delivered halfway up the slot at the back of the firebox.
- reduced transition from primary to secondary afterburner to 4.5"x4.5".
The thing behaved poorly, it was tough to get a clean burn, and in the course of playing around, even blocking the secondary air completely at the cleanest part of the burn (which was still barely clean) seemed to make no difference that I could observe. With most of the burn happening prior to the air injector except at the highest parts of the burn, the secondary air injector seemed unlikely to be contributing much at lower burn levels.
I don't know how big a role the reduced transition size made, but I suspect it was too small, possibly accounting for much of the bad behavior. I hope to run this with the throat back to 4.5 x 5", and again with the secondary air injected before the vortex.
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Post by Vortex on Jan 10, 2019 4:12:57 GMT -8
1st video looks good. Your 4.5" X 5" (22.5sq") restriction is around the same area as the 9" X 2.6" (23.4sq") which I found to be best on my outdoor setup. The air coming in around the top of the glass is disturbing your double vortex. Did you try closing that during the first burn so there was no secondary air?
Your second video looks like too much secondary air and too tight a restriction. If you can find a way I'd recommend trying a out small amount of heated secondary air in from either side at the front of the port (other end from your window), about 3/4" X 1/2" either side. I found that was the best of all the different configurations I tried, but even that didn't have a huge effect on it. My present setup has heated secondary air up through the ash trap, it mixes nicely with the gases before entering the port.
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Post by DCish on Jan 10, 2019 14:21:48 GMT -8
1st video looks good. Your 4.5" X 5" (22.5sq") restriction is around the same area as the 9" X 2.6" (23.4sq") which I found to be best on my outdoor setup. The air coming in around the top of the glass is disturbing your double vortex. Did you try closing that during the first burn so there was no secondary air? Thanks, I appreciate your input. I wasn't able to close the secondary air at all in the first burn because how I stacked the bricks had the top brick sticking out 1/4". I do concur that there is too much secondary air and too much restriction. I like the idea of playing with secondary air, but am having trouble visualizing your secondary air descriptions. Any chance you'd be able to sketch them and post them? I am particularly curious about how you supply secondary air through your ash trap -- I'm having trouble imagining how it doesn't end up adding to primary air and boosting gasification. On my last iteration of builds I supplied secondary air by opening a gap in the firebox roof one brick away from the slot and covering it with another brick to varying degrees. It seemed to work reasonably well, introducing extra air at the top of the burn box to be mingled, then mixed well in the turbulence of the slot. |
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Post by Vortex on Jan 10, 2019 15:58:49 GMT -8
This was the configuration that I found worked the best. My firebox roof/afterburner floor was made of 2 sheets of vermiculite board on top of each other. Top one had a gap at the front on both sides (where the dotted lines are). On top of the channels that the gap formed were 2 thin pieces of sheet steel: the steel glowed red hot, air came in from either side into the front of the port. (Picture is looking from above the port towards the front of the stove):  Another version involved putting thin pieces of steel between the 2 sheets of vermiculite board shown above, so there were thin gaps down both sides of the inside edges of the port. The board would glow when it got hot so heated the air coming in from the outside edges. I tried 1mm, 2mm and 3mm thick gaps. It worked alright but disturbed the vortex making it jiggle about. Yet another used a sheet of thin steel covering the whole floor of the afterburner chamber from the stove front, back to the front edge of the port. I again used 1mm, 2mm and 3mm thin pieces to hold it up and allow various amounts of air to flow in under it from the front of the stove, coming out in a line level with the front of the port. It didn't work as good as the original one pictured at the top. My 'secondary air' is a 38mm / 1-1/2" round hole in my ashbox door. The air comes in and is heated as it moves through the ashbox compartment then enters the firebox up through the 6" X 1-1/2" ash-trap slot, which is 12" directly below the port. Of course some of it gets used up in the firebox, but just as with the primary air, a lot just gets heated and mixed up with unburnt wood gases, and passes through the port into the afterburner and get burned there. The air up through the ash-trap is also excellent for burning up the charcoal quickly, it looks like a blacksmiths forge at times:  |
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Piet
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Post by Piet on Jan 14, 2019 0:53:26 GMT -8
I really like these developments. I loved Peter's DSR and I am sorry that it's not very reliable. I also like the perfect looking rams horn's from Vortex Aryan style stove.
Vortex, seems like you are developing these 2 into a great burner! I also like the features you add such as the ash box and the way you inject sec air without the need of using parts that would need replacement sooner or later.
1 question though: Sec air inlet via the ash box and then injected as shown in the drawing but how to you get it from the ash box into those channels? Btw, I am sure that you could replace the thin metal sheets with some ceramic glass as a sustainable alternative.
Brian, I also follow your experiments with great interest. I would love to see a photo of the whole setup.
Keep it up guys! I might build one of these myself!
Piet
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Post by Vortex on Jan 14, 2019 3:38:54 GMT -8
Thanks Piet, They were 2 different ways not the same one. In the one pictured above (on my outside stove), the air just entered by a hole on either side of the stove. That was the best I found in my experiments, but even that didn't make a lot of difference, and a large amount of secondary air actually made things worse.
I just used steel as it was readily available, ceramic glass would work just as well.
On my new inside vortex stove there already were 2 different primary air systems and a secondary through the ashbox, that feeds heated air up through the ash-trap into the firebox. So when I made the casts to try the Aryan afterburner out on the inside stove, I didn't bother trying to add a secondary air system, thought I'd see how it went with what I already had first.
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Post by DCish on Jan 14, 2019 18:01:33 GMT -8
I would love to see a photo of the whole setup. Thanks, Piet. Unfortunately, the "whole setup" such as it is is what is represented in the photos and vids here. It isn't a finalized indoor stove yet. |
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Post by wiscojames on Jan 14, 2019 18:40:13 GMT -8
A wider angle shot?
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Piet
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Post by Piet on Jan 14, 2019 23:03:37 GMT -8
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Post by DCish on Jan 15, 2019 7:02:22 GMT -8
Maybe I'm just not understanding the sort of shot you're asking for. Here is a re-post of two of the early pictures on the thread. What part were you looking for a wider angle shot of?   |
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Post by DCish on Jan 26, 2019 6:05:26 GMT -8
Did another burn last night. Changes: - Transition from primary to secondary afterburner chambers: 4.5 x 5.5 - Secondary air delivery is 2" diameter delivered 3" below the slot - 8" wide at slot (slot is 2", 3" on either side... this is the same as before) Cleaning up after last burn. Funny how the ash deposits on the secondary air viewing glass show the vortex pattern...      Refueling just after high burn, coming back up to speed. Top of burn Ran like a champ throughout. Secondary air seemed to make a difference only at the very top of the burn, so I'm sure that means I had lots of excess air. Likely next steps: - Flip port so that the short portion of the "L" shaped brick ends at the far instead of the near side. I don't expect this to change much except perhaps a bit of the shape of the vortex. - Build an airtight version. |
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Post by Vortex on Jan 26, 2019 10:58:20 GMT -8
Oh that's looking great Brian, well done.  Your double vortex looks a little 'scissor handled'. 9 inch wide seems to be the ideal size, but of course it's awkward to make the afterburner wider if you don't have any larger bricks or slabs for the roof. The rams horn in your second video is being perturbed a bit by the secondary air. Try it with the pipe so the open end is down in the embers. I find I get just as good secondary combustion that way and it doesn't disturb the double vortex. |
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