The previous post described a sea-urchin-style fire path: the fuel input tube looked like, and acted like a chimney. That attempt grew from an observation that there simply wasn't enough fuel burning at any one time. Extending in one plane, the vertical plane, is apparently the accepted and traditional technique, near as I can tell from looking at the Internet photos. Well, it sure didn't work for me.
There are a couple more dimensions available.
The previous firebox - the place where the fuel starts burning, not the "reactor chamber" - was approximately (and roughly) a nine-inch cube. Actually it was more rectangular in one horizontal dimension so it was maybe 9x12x9. The failed tin chimney extended a 9-inch face vertically.
This week's modification leaves three faces of the original firebox cube in place but extends the other three into several dimensions.
The new firebox is taller, rounder and successfully blackened in the photo above. The three original faces of the cubic firebox are at the bottom of the cylinder but you can't see them in this photo. The large dark square at the lower right of the photo is the exhaust. Interestingly, the only part of the exhaust port that seems to be necessary is the top two or three inches of that square.
Looking into the fire. There are air intake ports indicated in blue (located around the left side in the first photo). The flat, cubic remainders of the original firebox are identified by the red arrow.
Operation is a wee bit freaky. The experimental lid for the firebox (firetube?) is a peculiar old iron disc with an iron pipe for a handle. It gets quite hot as it sits atop the fire. Feeding the blaze results in either a face full of fire or a face full of smoke. The iron/mud interface is pretty leaky as well, so each feeding necessitates a re-caulking of the seal around the lid. Treacherous. The kind of work 11-year-old boys were hired to do a century ago.
The air intake ports are arranged at an angle on a curve. This is cute and challenging to build but needlessly complex and the overall volume of air intake ended up being way less than I intended. A buttress and manifold for the angled intake ports is located around the lower left side of the cylinder. A brick and ambition shortage caused this to be rather small for its britches as well.
Despite the clumsiness of the feeding arrangement, the first two firings went rather well. When left alone to manage itself, all the fuel gets consumed which was a chronic problem with the too-small firebox designs. Rather than tinker around with this firebox tower, I'm leaning (heh) towards tearing it down and re-building, this time keeping only two faces of the nine-inch original firebox; the bottom and the "tunnel" faces.
The resulting cylinder will be about the same diameter but will maintain that diameter all the way down. The air intake ports will be arrayed to the left for atmospheric air and the new ports on the right will bring in pre-heated air from the exhaust. In the center, directly across from the tunnel, is a clean-out door. This design being more geometric shouldn't require a buttress and should be much easier and efficient to build. Variable angles are fun and pretty but troublesome.
Pro-tip: rotten, fall-apart-in-your-hands landscaping railroad ties that were soaked in petroleum as much as 75 years ago or more are still too rich for Mudfire. The smoke was heavy, wet and stinky, resulting in the garden hose being directed into the firebox.
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