Project: 170mm (6.7inches) ceramic batch box bed and cooker

[peterberg]

Even a bog standard stove won't work properly under these circumstances! Air tight, dimensions according to specs and with a proper chimney would make a world of difference. And oh yes, I used a spark screen while running open.

[Orange]

ok, the firebox opening is too big, Peter reduced it with the door and a mesh so the gasses can't escape easily. And his chimney draw is way better.

[drooster]

I'd like to add my encouraging words to Orange's setup. Do exactly as Peter says and carry on.

[Orange]

main bell construction - looks simple but a lot of manual work:

I'm not a pro at this but the door works:





steel pipe is 60x40mm - for a 150mm system and I have 170mm system so I've enlarged openings below for primary air:



with this air flow shouldn't be restricted (only a bit from this opening to side slit):





bypass - around 1/3 of system size:

side slits for primary air according to specs:

top view - on right side comes firebox, on left is the opening to secondary bell:

needs additional grinding...



top view of primary bell:

[martyn]

I can just imagine the amount of work it took!
Looks like a proper job though and I am looking forward to seeing the next step.

[Vortex]

Well done. Took me 3 months of my spare time to do all the metal work, takes a lot longer than you think.

[Orange]

yea if you don't have a lot of free time my advice is buy a tested finished product because here you have to account also finding and acquiring materials, drawing, planning, building, testing, debugging etc.

[Orange]

here's the whole thing. Doesn't run well, details below:

inside the bench where gasses exit 1st metal bell. On the left are magnetite bricks for faster and longer heat transfer, 1 layer of standard bricks above for faster bench heating:

bench tunnel to the chimney. Hollow bricks + rockwool are facing wall to avoid heat transfer. Floor is from air concrete + clay (and OSB+EPS below):

mill scale grinded. Not sure about which coating to put:

top view 1st bell - minimalistic lightweight core (30mm firebricks):

CFB riser and top box. Exit port on the side to reduce stove height:

front view:

had to wear a mask while cutting CFB like it's a virus. It's coated with waterglass + clay mix:

doesn't run well, smoke comming from front:

went with backup plan - fully enlarged exit port (like on batchblock). Now it works better, doesn't smoke back like before. But I don't think it's burning clean because of dirty firebox and max chimney temp 120C with bypass (1/3 system size) open!!

I loaded only 1/3 of batch but didn't expect such weak results:

you can see the black firebox:

additional details:

- BB dimensions and ISA are pretty much according to specs

- chimney is not insulated but worked flawlessly with the basic metal stove

- fire burns better with door opened than closed (I guess that's expected with more air)

- smoke sill comes from the front door even with enlarged exit port when bypass is closed (and chimney temp goes below 50C)

- upper window is useless, there are no flames and window gets dirty but I haven't burned full batch yet

- bench is not heating properly, I might remove wall in the middle to help with gas velocity and draw

suggestions welcome before I demolish part of the bell.

[fuegos]

I'm sure someone more knowledgeable will be along soon but i was wondering what it runs like with the bypass fully open ? Also how many M of chimney do you have ? maybe the non insulated stovepipe & metal bell are radiating too much heat ?

[martyn]

I cant offer any in depth technical advice but I think that most riser less cores require a good strong chimney draft so an insulated flue might help.
Wet or damp materials are always going to hamper performance and it takes time to dry out all the mass.

[Orange]

here's how it runs with bypass fully open (bypas opening is 1/3 system size CSA):

chimney is this 2m metal pipe + 4m refractory pipe uninsulated. It worked flawlessly with the basic metal stove and ISA  isn't huge so I expected no problems.

so yeah I'm thinking about increasing air velocity by removing restriction in the bell or insulating chimney (or both).

[Vortex]

I'm no expert on dsr2's, but the fire doesn't appear to be even making it to the port? It looks like a small fire in a large firebox, which most designs don't cope with well. Without the secondary combustion it cant burn clean, and without a fire big enough and hot enough to heat the firebox up properly it wont burn off any soot from startup on the ceiling. It also wont heat the chimney enough to create a good draw, as the large mass will take up the small amount of heat before it makes it to the chimney, which would explain the very low temps you're seeing there. Have you tried a full load of dry wood? Is the mass still damp? Only thing I can see in the mass that maybe could cause a problem is all those vertical ridges down the sides, that would increase the surface area but also create drag. Hope you can get it running right.

[fiedia]

Hello Orange,

I built a 125mm batch (vertical riser)  with the same door design. I am no expert but I noticed  some details that may help :

- primary air frame: I used 50mmx50mm square tubes for the frame (30x44 openings). For your 170mm design, I understood that you use 60x40 tubes. May be you do not allow enough primary air inside your firebox. For my next design (200mm riser) I scaled it to 80x50. 

- air inlets: in case the frame is too narrow, I am not sure that opening above each air inlet helps much since the air still has to go through the vertical tubes.

- primary air slits (on each side of the door): The door design posted by Peterberg is not optimized. He did lots of trials with different slit sizes and even a third one on top. On his advice, I played with the slit length. best results were given with higher and shorter slits (10% of riser CSA each, same as bottom inlets). You can find it here. Longer slits = overdrive and lots of dark smokes.

- coating: I just put oil the frame and it protects quite well against corrosion but not against water coming from condensates. The top window and its frame are a cold source. I get condensation there, inside the stove when smoke temp is too low. Water is then dripping along the steel and corroding the whole inner side of the frame.

[satamax]

Orange, insulate that chimney. That would be the first step i would take on a lazy burner. And, check and recheck for constrictions. I bet there is something you overlooked, which is restricting your draft.

[satamax]

Well, i know Peter likes his designs tight. But that exit on the top left is way too small in my opinion.