Air flow paths and reburn chamber

[wahoowad]

I'm confused how any unburned gases enter the reburn chamber at the top of my Jotul 3CB firebox.

I have two air inlets/controls at the front of the unit that appear to provide combustion air into the front of the firebox. I observe the flames and they seem to flow up to the ceiling (which is actually the floor of the reburn chamber), then forward to slip past the gap at the top of the firebox and into the top part where the exhaust vent is located. The reburn chamber has a bunch of holes in the leading edges as if gases or exhaust flows though them somehow, but I do not understand how any of my unburnt gases actually get into this area to be reburnt?!?!

 

[wg_bent]

I think those holes just allow super heated air to enter whereby the hot air ignites the unburned "gases"

 

[wahoowad]

Warren,

I could follow that if maybe the air entered that chamber from behind and flowed through it, but why would air bother entering a confined space when it has a free exhaust path up and out?

 

[wg_bent]

The design of your stove plus the chimney pulls air into the stove's primary air, the air is divided so that it gets pulled through the air wash system. How they manage to do that in your stove is the element of the design engineering that I'd have to see to understand, but all non-cat EPA stoves do this.

I remember Elk responding to a post where the person wanted to design their own stove because they were good with a welder...Elk's point on his response was that it's really hard to design a good stove, and many have failed with big budgets and R&D staffs. Airflow is the magic in an EPA stove.

 

[Mike Wilson]

I think "reburn chamber" is a slight misnomer. The holes you see are not porting gasses from the fire, they simply shoot hot air into the top of your firebox. The unburned smoke from the fire below it comes up, hits the new source of (hot) oxygen, and ignites, thus "reburning." You'll see what looks like flames from a gas cooking stove coming from these air ports. From there the flame will curve up and around your air baffle plate, and exhaust up the flue. No "burning" goes on behind (above) the baffle plate itself. Note, the baffle plate is suspended and separated from the top of the stove, so that the stove body itself does not act as a heat sink and cool the plate down (you want hot air coming out of the jets). Some stoves have insulation up there, I don't believe yours does.

-- Mike

 

[adrpga498]

I think "reburn chamber" is a slight misnomer. The holes you see are not porting gasses from the fire, they simply shoot hot air into the top of your firebox. The unburned smoke from the fire below it comes up, hits the new source of (hot) oxygen, and ignites, thus "reburning." You'll see what looks like flames from a gas cooking stove coming from these air ports. From there the flame will curve up and around your air baffle plate, and exhaust up the flue. No "burning" goes on behind (above) the baffle plate itself. Note, the baffle plate is suspended and separated from the top of the stove, so that the stove body itself does not act as a heat sink and cool the plate down (you want hot air coming out of the jets). Some stoves have insulation up there, I don't believe yours does.

-- Mike

Mike I have the catine and your exactly right. The burn isn't inside the baffle as one may suspect. If the fire isn't too high not all levels (3 on mine) will show air movement.

 

[wahoowad]

So let me see if I get this right. The reburn chamber (2 rows of horizontal holes) is not fed with any combustion air from outside my stove and has no appreciable air flow through it. Gas reburn occurs when unburnt gases flow up and past the holes and somehow superheated air from inside the chamber ignite them. The reburn happens outside the chamber, not in it.

I guess I thought the reburn occurred inside the chamber given how I see jets of fire seemingly shooting out. Somehow I suspect there is still a circulation of air (perhaps coming in from the upper row of holes?) given how the jet of combusting gases must stimulate air movement from within the chamber.

Today was my longest burn and I have observed it a lot through the glass door. Also watching how the stovetop temps vary based on the type of combustion going on.