New Secondary Air arrangement for a batch

[matt walker]

Hey gang, I've been experimenting like crazy with my stove these last few weeks, and am on to something sorta cool. I made a post about it over at Donkey's board, and thought I'd open up the discussion here as well in case any of you are interested in this minutiae.

It's a secondary air tube placed directly in front of the port. It runs vertically the full height of the port, and about 1"-2" back from the port entrance. There is a slot running up the side of the tube facing the port. I've designed and built a few different arrangements, with different results, and am not set on one configuration yet. Generally though, it's a secondary air delivery configuration with a CSA of about 9% of system CSA, positioned to inject the air directly in front of the port, while adding beneficial turbulence patterns.




Look at the clean burn time here, it's a very different rate than normal...

[matt walker]

Here's the full story over at Donkey's...

http://donkey32.proboards.com/thread/14 ... rrangement

[mannytheseacow]

Very cool, Matt. I had several questions/comments but see it's already been covered over at donkey32.

Those flow patterns are old news in the world of fisheries. Eddies and vortexes have been well published, so if you're seeking any additional info on that try searching in the fisheries research.

It's cool to see several graphs like you showed @ Donkey. Once you get it dialed in you should weigh your wood, same species/dryness, and run 5-10 burns with and 5-10 burns without for solid data.

[matt walker]

Thanks man. Check this out...

[mannytheseacow]

Wha....? Whoa. I don't even get what I'm seeing. There seems to be little fuel in it, and the flames are hitting the top of the burn chamber and coming back forward? Hard to tell which way things are streaking through the port. I imagine it's going out but sometimes it looks like it's coming back in?

[matt walker]

I think that there is air coming in from the bottom of the window in the door, cruising up along the top, and what we are seeing is the wood gas/o2 flame front creeping towards the air source. I think, I'm not sure. It may be an air leak through where the original P-channel was in the ceiling. Whatever it is, it's cool looking!

Manny, I'm excited to share this with you. I'm living with it for a few days here, although I'm still running the tester and tweaking it a bit, I'm more interested in if I'm headed a good direction as far as livability and function. So far, I think it's going to be amazing. I seem to be going through way less wood all of a sudden, since the burn cycle is so much longer, and I think I'm really slowing down the movement through the flues, so I'm transferring more heat per load. I'm not sure of that, but it seems that way right now. I can keep the barrel at 500 for around an hour on one three stick load, and then coaling keeps it at 400 or so for another hour. I may be full of it, and I'm still a bit scared of back drafting, which with that box full of smoke could be gnarly. But, so far, it's pretty promising.

[mannytheseacow]

Amazing. Slowing down velocities while retaining efficiency and high temps would be amazing. Any way to gauge temps in the core? What's the life expectancy of that air injector? Seems like with the CO levels you're seeing, back drafting isn't much of an issue even if it does happen.

I can't find the old thread... But am I crazy or was your old stove testing higher on the eff? I know there are I'll the other factors and variables but I thought the old one was slightly over 90?

[matt walker]

I had some high efficiency readings early in October due to the wet bench making exhaust temps super cool. The standard batch is capable of (I think) slightly better numbers but not sustained for any length of time. This one does better on CO than I ever saw my standard batch do, but the standard batch can handle a big huff of wood gas, which translates to low O2, which translates to high eff. All told though, I think this one is doing way better taking the whole cycle into account. That may not be right, I'm still sorting it out, this one does have a long coaling stage which isn't good for CO. We will see...

Oh, I don't know about the life of the parts. Peter always maintains that the cooling air helps them live longer, but this thing is cherry red when you look down it from the entrance, which is part of why it's working so well I think. Super heater air.

The back draft issue I'm scared of is a gust of wind reversing things momentarily and blowing up the wood gas in the box. You are right though, there isn't a whole lot hanging around in there, it is moving all the time, albeit slowly.

[Nirky]

Is there an simple/easy way to incorporate this mod into an already built rmh?

[mannytheseacow]

I'm also curious about Nirky's question; any application for a J burner? I'm guessing the answer is "I dunno, try it and see."

I'm also curious, Matt, about the heat you are getting off that thing. I get heat radiating from the barrel, of course, but I get a tremendous amount of instantaneous heat pouring out of the feed. I imagine you don't get that anymore with the batch box?