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Post by DCish on Jan 8, 2016 18:07:24 GMT -8
I would think the leftover ash would decrease as you insulate the burn box and close off the gaps. The glow phase was probably shorter from the box cooling down faster and losing some draft to keep glowing? Yeah, that's my assumption and hope as well. Fingers crossed! |
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Post by DCish on Jan 8, 2016 18:09:19 GMT -8
Dang, DC!!!! You've been killin it with your bricked up test! AND, I've been away too long  great work, anxious about the final product.... Eric VW Thanks Eric! Have another config test idea to try this weekend, weather permitting. Rain on the forecast, though. |
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Post by DCish on Jan 8, 2016 19:49:44 GMT -8
Usually everything is reduced to fine white ash, occasionally I get one or two fingernail size pieces of charcoal left, never anything more. Normal firebrick makes the fire less efficient at the start because it's sucking heat, but it gives it all back at the end of the burn. Thank you, very helpful. I'm thinking to do a more robust/sealed off build in a couple of weeks and see if that helps. |
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Post by DCish on Jan 17, 2016 5:33:27 GMT -8
Been doing a series of burns with slight modifications to the afterburner. Of course my battery died so I have minimal pics to share.
1) made first baffle (immediately after the port) taller. It is now 9" tall, same as the port, and 2" to the left of the port. I now get a near perfect double ram's horn before the flow changes direction to go over the wall.
2) pushed it hard by throwing lots of small sticks in early in the coaling stage. The flame front grew up over the wall and into the chimney. The burn got noticeably dirty until the afterburner came up to temp. Even after it was up to temp it stayed a bit dirty. I suspect this is because I have less than recommended flow through the secondary air supply.
3) added a downdraft baffle just before the chimney so gases would dwell in the insulated afterburner area longer. This did distribute heat more evenly along the front wall of the stove.
4) Cut an upside down "v" in the baffle equal to the area of the port. The goal was to introduce a final bit of turbulence during high fueling events. As near as I can tell, only the most massive overfueling events brought flame this far into the system, and even then, I'm not confident there was any added value from turbulence at this point. Without a gas analyzer I'm not sure if I'll be able to see a difference.
Next step:
1)drill more holes in the secondary air supply.
2)more baffle tweaking
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Post by DCish on Jan 17, 2016 21:27:43 GMT -8
Ok, some more testing of a different baffle today (didn't get to adding more secondary air holes). New baffle. 5" hold gives same area as the 2" x 9" slot from burn box into afterburner (~19.5 sq in).  Warming up. Note the turbulence after the baffle (no second baffle installed at this point, straight pass-through to chimney after first baffle)  . Video . Second baffle now in place (forcing gases down before chimney). Up to temp. If you look closely you can see some interesting turbulence.  Video Well up to temp. Video Peak of the burn (bricks up to temp, second small batch of wood [four 1" pieces of wood] maxing out). Flame running whitish / bluish, very hot.  Video Shilo, Peter, Adiel - I know you've been doing a lot of comparing how flame looks to how it reads out on the testo. Does anything I've posted here give you any basis for guessing how well this is burning? Thanks! |
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Post by pyrophile on Jan 18, 2016 1:11:26 GMT -8
Hi!
I find this round "slot" interesting!
What about a round "slot" in the port of a batch box firebox ? or in this cookstove's firebox?
Benoit
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Post by pyrophile on Jan 18, 2016 1:25:32 GMT -8
And what about having this hole in the middle of the baffle instead of being in the upper part?
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Post by DCish on Jan 18, 2016 5:50:40 GMT -8
Hi! I find this round "slot" interesting! What about a round "slot" in the port of a batch box firebox ? or in this cookstove's firebox? Benoit Thanks Benoit, that is an interesting idea. I've always considered Peter's vertical slot pretty much ideal, because it allows for direct pass through of air both when the firebox is full and when it is in the coaling stage. It also produces that great double vortex when transitioning to a riser. A circular port should theoretically produce a toroidal vortex, which presents some very cool possibilities, but I think the complexity of that rebuild is beyond the scope of my tweaking at the moment. Definitely something to keep in mind, though. |
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Post by DCish on Jan 18, 2016 5:59:01 GMT -8
And what about having this hole in the middle of the baffle instead of being in the upper part? I decided to do the hole in the top of the baffle because I noticed that the double vortex didn't form after the batch box slot if there wasn't a contained space immediately after the slot that forced the flame front up before turning away from the slot. Still, it might be a fun experiment, and it's not too hard to cut a hole in a scrap of sheet metal. Probably a first experiment would be to fire it up with the current baffle inverted so that the hole is at the bottom. It might be curious to see what happens when gases from the top of the slot are forced down to the hole. If that gives interesting results, putting a circle in the middle might be an interesting next step. |
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Post by peterberg on Jan 18, 2016 6:38:53 GMT -8
Shilo, Peter, Adiel - I know you've been doing a lot of comparing how flame looks to how it reads out on the testo. Does anything I've posted here give you any basis for guessing how well this is burning? Results with the Testo were best with a very uniform and rapid movement of the flames, low in the riser in particular. Also, very clear and even translucent flames yielded good results. Looking at your videos, I would say it looks erratic and sometimes even chaotic, the flames further down the path are clear but aren't right behind the first port. I won't go as far to say it isn't mixing that well. The pattern isn't regular and steady but without a gas analizer it's impossible to tell whether it's good or not. |
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Post by Karl L on Jan 18, 2016 15:39:09 GMT -8
I've been thinking about why Peter's vertical batch box slot, combined with the 'S-portal' or the 'Walker port' might work well.
These arrange the burning wood gas and the secondary air as three flat sheets or layers. These layers have a large area of contact with each other, which gives more opportunity for the air and wood gas to make contact and react (burn). The turbulence in the double vortex is then even more effective, because the layering has already done a lot of the mixing.
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Post by DCish on Jan 18, 2016 18:29:54 GMT -8
Results with the Testo were best with a very uniform and rapid movement of the flames, low in the riser in particular. ... Thanks, Peter, that gives me a target for observing future burns. Some of the irregularity may be due to how I am operating it. As I recall it seemed to get a good double ram's horn early and low, and get more chaotic over time as I burned a bunch of small diameter stuff and a tall pile of coals accumulated, obstructing the lower 1/3 of the port. I'll have to do a more realistic burn and keep a good eye on flame uniformity low in the riser. The "uniform, rapic and low" observation is particularly good news given that I had to stoke it unrealistically hard to get flame much past the first baffle. Thanks again! Anybody in the DC area with a Testo or similar equipment? I'm willing to work out something to make it worth your while to come by for an afternoon of testing! |
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Post by DCish on Jan 15, 2017 21:10:31 GMT -8
Quick update post. I haven't had lots of time to tinker for a while, but I did get a good 5-6 more burns in over the past two months or so. All of my recent runs have been similar to the above in that they have one version or another of a "riser stub" to push the flame up above the level of the top of the port so that the double vortex forms (same as it would in the bottom of a riser) before sending the flame forward toward the front of the stove for fire viewing. The problem is, unless it is being stoked relatively hard, a lot of time at the beginning and end of the burn the flame never gets appreciably beyond the top of the riser stub -- not much good for fire viewing. I have pretty much decided that the riser stub has to be sacrificed if I want any appreciable fire viewing to happen after the slot. PNW Dave just posted a build with a variation on the Walker core very much in the direction that I'm moving ( donkey32.proboards.com/thread/2163/walker-riserless-core-retrofit). I have a couple of ideas for tinkering with variations on the riserless forward run to see how various tweaks influence mixing, and will post the outcome. I may not end up coming up with something original, but all the tinkering is a really fun exploration, and I'm getting much more comfortable with the idea of bringing this thing inside eventually. I may be on the multi-year plan, but I do hope to eventually graduate! |
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Post by DCish on Jan 20, 2017 19:54:24 GMT -8
Feeling inspired tonight after reviewing Peter's latest thread (http://donkey32.proboards.com/post/23421/thread). As I mentioned there, looking at his design confirmed something I've been thinking - the critical element for the double ram's horn is a 90 degree transition following the slot. If that's so, and his 45 degree slot out the top works, why shouldn't a slot out the side work (Basically, Benoit's idea from 18-Jan-16 on this thread)? Tonight's rough mock-up had a 4.5" x 4.5" square port in the left wall midway up. It dumped into a 2" wide slot 18" high coming back toward the front. It's clearly chaotic and crude, but even with the poor dimensions you can see the flame trying to curl around into a double ram's horn. I plan to tinker some more, but here's video of the quick and dirty test confirming that the double ram's horn is plausible in the horizontal configuration.
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Post by peterberg on Jan 21, 2017 7:52:08 GMT -8
It looks like it's working as intended, very interesting! I agree, the flames seem to struggle to curl around, maybe the slot should be wider than 2". And this is side slot of 4.5" square halfway height and front to back? What's the size of the core? Chaotic is good, turbulence doesn't need to be tidy. This could be the start of a new development, the physics of the double vortex and how it is formed isn't fully understood yet, in my opinion.
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