lawry
Junior Member
Posts: 113 
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Post by lawry on Jan 22, 2016 1:50:22 GMT -8
Hi all I have built a 6" PvdB batchbox cook stove with an oven. I need advice on the following: 1. The emissions when I start look horrible. How long should it take for clean combustion to occur? Peter when do you start your measurements? 2. My oven doesn't go above 120•C. Is it because it's not insulated? It's a black oven (literally) I plan to change to white but I would like to figure out how to raise my temps first.  |
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Post by peterberg on Jan 22, 2016 5:24:55 GMT -8
I start the Testo again when the oxygen level is 20% or lower. So the diagrams show ALL of the relevant burn time. I'd suspect the construction of your batch box is somewhat different. The cooking plate too close to the riser, too large oven or restrictions in the exhaust to the chimney. In general: when the gases are forced into a downward turn, being 90 degrees or 180 degrees, the available space should be AT LEAST 150% of system size.
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lawry
Junior Member
Posts: 113
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Post by lawry on Jan 22, 2016 11:14:06 GMT -8
Thanks Peter. It should be the 150% system requirement then. The riser and cooktop gap should be ok. I took it apart today, I'll correct the turns.
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lawry
Junior Member
Posts: 113
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Post by lawry on Jan 24, 2016 6:08:48 GMT -8
I've corrected the turns and i must say.... the smoking and draw have improved vastly! Even during light up when i open the plates the smoke is sucked in! When i add more wood it used to also smoke. That has also stopped. Thanks PvdB! Here's the cooktop temperature profile:  Here's the door with air wash (did it myself). I also broke the robax glass.  The remaining challenge is getting the oven to 250°C. Since its a black oven it needs insulation i guess, especially bcoz its a single skin stove. I will retrofit a mild steel oven box. The stove is prototype for testing combustion concepts. It has a P-Channel and wood gas recirculation. I plan on building a prettier one in my outside entertainment area (lapa) |
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Post by peterberg on Jan 24, 2016 7:32:07 GMT -8
You're welcome. Always good to see one of my quessings is right. Insulation around the oven would help to ramp up the temp. Since you changed the thing recently: keep firing it to dry it out completely, this will take some time.
May I suggest that exhaust gas recirculation in this design may or may not work? It's unproven whether or not it will make any difference. It's even unsure any possible difference is positive or not, even Shilo isn't so sure anymore.
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Post by peterberg on Jan 24, 2016 7:47:04 GMT -8
Lawry,
I studied some more of your pictures in another thread and it seemed to me that the port isn't central in the riser but on the side instead. The flame in there is off-center and won't mix as well as a double vortex. You can get a much higher temperature out of the thing when you change the port in such a way that it is centred in the firebox and riser. The double vortex should be equally strong at both sides and your cooking plate directly over the riser could easily reach 400 C since your system size is 6". Been there, done that in 2013 during a workshop.
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lawry
Junior Member
Posts: 113
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Post by lawry on Jan 24, 2016 11:40:49 GMT -8
I will definitely build it as you suggest so that I get the Rams horns. On my permanent installation I'll do it proper. This stove started as a J Tube so it was a bit difficult to try and Centre the port. I hear you on the EGR. Here is what I got from my tests. I just don't know if there is any benefit...  |
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morticcio
Full Member
"The problem with internet quotes is that you can't always depend on their accuracy" - Aristotle
Posts: 371
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Post by morticcio on Jan 25, 2016 15:47:11 GMT -8
It looks like your riser is made using firebrick splits. Is it insulated - maybe you backfill with perlite or ceramic blanket?
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lawry
Junior Member
Posts: 113
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Post by lawry on Jan 25, 2016 22:32:13 GMT -8
It looks like your riser is made using firebrick splits. Is it insulated - maybe you backfill with perlite or ceramic blanket? Yes it is splits. And yes it is insulated with ceramic blanket. |
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lawry
Junior Member
Posts: 113
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Post by lawry on Mar 21, 2016 11:24:22 GMT -8
The remaining challenge is getting the oven to 250°C. Since its a black oven it needs insulation i guess, especially bcoz its a single skin stove. I will retrofit a mild steel oven box.Just an update on my prototype modifications. I have now changed my oven to white. I have also used cast slabs above the oven instead of my sagging bricks "workaround". The gap around the oven is more uniform now. I can now get the oven to 240C.  Cookies came out nicely. Well wife says they are over cooked. I also baked beef bourguignon... Of Sorts. I have designed a cast iron cooktop. The patterns are done i now need to get them cast. I will update when i receive the top. Thanks again to the members of the forum for sharing their accumulated knowledge. |
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