BOOH IV

[Nutcase]

So when I got into my workshop and considered my options more carefully, I ended up doing something a little different from what I indicated at the end of the last thread. Basically, I cut the 2' long burn chamber in half and rewrapped the pieces into a 1' long cylinder around an 8" core. I then used a section of the wire mesh already bent into a 14" channel and a piece of stainless sheet also prebent into a 14" channel to make a composite frame to hold the chimney and the burn chamber together. Then I tacked on an end cap/6"x8" fuel inlet framed in another piece of stainless sheet prebent into a 12" channel.

[Nutcase]

Generally speaking, the details of this construction remain extremely expedient and too crude to warrant much attention. However, there was one thing I'm a little bit proud of



I secured the wire mesh channel to the stainless by simply running a thin strip of aluminum extrusion that happened to be handy. This served very well for the purpose and of course it is entirely reversible. Almost as nifty as the wire mesh barrel stand.

[Nutcase]

So we put the barrel on and did a burn. Here is a picture of about 2/3 of the fuel we ended up using.



The fire did not start running horizontally on it's own like BOOH III. However, blowing strongly on it once was sufficient to get it to turn. I didn't put enough small stuff in to get it up to temp at the outset, so it didn't come up to temp or stop smoking quickly. Also it became apparent that the fuel inlet was too open in the front. 10 minutes into the burn, the top of the barrel was only at 150, and the smoking had only tentatively subsided. Here's a photo from this stage of the run, showing small stuff on the bottom that is not even ignited.




However, with a random chunk of Roxul framing the inlet, some more small fir pieces thrown in and the "big" piece of ash taken out temporarily, it began to take off. At 12 minutes the barrel top was up to 300. Here's a shot from around that point in time.



You can see a bit of liquid boiling out of the end of the ash.

[Nutcase]

From there, the temperature of the barrel top rose rapidly. Four minutes later, 16 minutes into the burn, it was at 600˚F. At 20 minutes, it was at 750˚F. After drifting back down to about 600F, my wife said, " I want to see what it takes to get to 800˚F," and threw in some more small pieces of fir.



Then we let it burn down. At 40 min it was down to coals and 350˚F.

I hope it doesn't rain tonight, as I didn't get around to moving everything under cover after it finished burning down and cooling off.

The temps are all from the center of the barrel top, directly over the chimney, by the way. They fall off rapidly from that point.

I will probably have a few more comments after I take this system apart tomorrow.

[Nutcase]

This is a pottery shard that my wife put into BOOH IV as a contact point for the sticks. You can see some of the ceramic blanket material adhering to it. The glaze has fluxed the blanket material, i.e., lowered the melting point where there was contact. Not unexpected. The shard also broke into three pieces during the burn, also not unexpected. Seeing is believeing, though.



Here you can see what happened to some fiberglass peeking out from between layers into the burn channel. I had used it as an aid in wrapping two separate pieces of blanket into one tube. Because of a cutout from the previous construction, this exposed a patch of the fiberglass at the top of the burn chamber near the fuel feed. The center of the patch is completely gone. the edges are melted and brittle. However the material actually protected by a single layer of the blanket is preserved. Also it's worth noting that this material hasn't fluxed the blanket.



Finally, this is a shot of the bottom of the end cap/fuel inlet piece. The point of note here is how the inside layer has collapsed as a result of the fluxing by the pottery glaze. The total thickness of the three layers at the edge has been reduced to about an inch.

[Nutcase]

Bottom line, BOOH IV approaches the performance of BOOH I without melting down or otherwise drastically deteriorating-at least in this brief test. The blanket is clearly vulnerable to mechanical damage, so the area around the fuel inlet will have to protected somehow. There is also the risk of some sort of accidental fluxing. However, at the moment, I don't see that the chimney actually needs to be any thicker or more solid than it is now. I may redo the wire mesh cylinder to make it neater and more cylindrical...

Well, actually the next step should be putting what I have back together again, with some revision of the fuel inlet, and see what happens if we put in as much fuel as it can reasonably accept. I can work on my technique for getting up to speed quickly, too.

[matt walker]

Wow, I just watched that furnace video. So, with a durable feed area, you might be able to have the entire works of the stove be "soft". Hmmm, very, very cool. Ok, wow again as I think about the implications more. Very cool stuff Nutcase.

[Nutcase]

Yeah, it's very cool. I may buy his book at some point. Since I got interested in the ceramic blanket material, I've ended up prowiing around more on DIY kiln and furnace boards than on rocket boards per se. Same general sort of people of course, but with somewhat different objectives and traditions. Lots of food for thought.

I'm still mulling over a lot of options about how to treat the inside of the rocket at this point. Is it worth the trouble and expense to put on a hard refractory layer? The commercial stuff costs on the order of $70 per cubic foot if you buy in 50 lb. bags. Limited shelf life, they say. An 8" circular system has an inside area of at least 8 sq.ft. Need maybe 3/16" to be really sturdy. so less than .2 cubic feet. But it's all ten times as dense as the blanket, though some stuff is supposed to have similar thermal conductivity. Still going to take that much longer to get up to temp. But is that important, really? pour a shot of vodka in there and light it off to get things started! It's a maze. Maybe it's better to just rebuild every now and then and keep it reeeeeeely simple.

Thanks for the feedback. It means something to me, makes it worth the effort. Takes as much time write these things up as to actually do them. More, actually, if you don't count the time I just wander around looking at things and thinking.

[matt walker]

Well, I'm thankful you take the time. You know where I stand on the performance/durability issue. I'm gonna take it apart and mess with it all the time anyway, is my thinking. It is a maze though, for sure. There are a lot of ways to skin this cat.

[Nutcase]

So I put BOOH IV back together, adjusting some details, but basically it is the same. The only point of some interest is in how I have used a strip of plywood to lift the chimney cage 1 1/2" so I could easily slip three layers of the blanket under. I also put in an old electric stove top element as a base for the sticks.




After a false start with too little small kindling and too much round stuff that isn't quick to light off, we got it going, using mainly a few pieces of fir. It accelerated rapidly. After the first minute, the temp went up at 100˚F/min up to the 900˚F max reading on the thermometer. My impression is that it didn't go a lot higher before plateauing. I'm not sure, we may have put in another stick from what you see here.