Post by matthewwalker on Nov 20, 2014 22:04:56 GMT -8
That's the p-channel, which is plugged, above the tube. Yes, the glass is in there but if I stay with this design I'll take it out. It's black most of the time when burning like this. And yeah, the flames are moving towards the front. I'm not sure if it's a leaky p-channel, or if the primary air from the window wash is cruising along the roof and the wood gas flame front is moving towards the air source, or what. It looked cool though, so I thought you guys would like it. It's warming up in that shot, eventually the box gets all glowing red and the show doesn't look like that anymore. I was really hoping to show the sheet of flame in the port, it's really something.
I might try holes, I had thought of it, but it's easier to measure a slot. Peter, you are right, the slot is 8"x.25" = 2"csa, while the tube is 1.25"I.D. so only 1.22"sq csa.
Drilling progressively larger holes or a tapered slot to the top is one method. Of course I've tried holes years ago but it's much easier to use a thin disk to grind the slot. The other method is a much wider tube and a straight slot, this will work as well.
It looks like the primary air is small enough now judging by the looks of it. So the excess air is coming from the secundary inlet(s). I would expect the inlet being slightly too large now, this could be compensated by using a wider tube and leaving out the second tube. This last sentence is pure speculation, I have to admit. Regretfully, I am not in the position to build a test bed at the moment.
By the way, the end temperature according to the movie is redicously low in my opinion. Most of my experiments wouldn't run sustainably with a temperature lower than 140 F. I'd think your heater is running at the very edge of what is possible in this respect.
Last Edit: Nov 21, 2014 3:43:00 GMT -8 by peterberg
Post by matthewwalker on Nov 21, 2014 10:06:45 GMT -8
Thanks Peter, yes, I'm running on the ragged edge for sure. When I cover my benches I typically will see more like 130°F at the chimney. This test you are seeing there is the first firing of the evening, benches uncovered, so things had cooled down quite a bit. It's surprising it's running so well. It's warmed up now quite a bit outside, I started these experiments last week when we were well below freezing. I was concerned things would change for the worse once it warmed up, but so far it's running well, although the exhaust is certainly lazy.
Peter, I sure wish you could test this along with me, I can only change setups once in the morning and once in the evening, as I have to burn to stay warm. Could you clarify your comment on the sizing. Are you talking about v3? v4 doesn't have the second tube, and is larger. It is I.D. 2.25"x1.25" for a csa of 2.8"sq. which is exactly what I was going for. 10% of a 6" system csa. Also, I was thinking about the size of outlet, and wondering what the temperature differences between inlet and outlet were doing to our csa flow calculations/speculations. Does it need to be greatly over sized at the outlet since the fluid is so much denser at the inlet? Man, staying warm is complicated!
I have an idea, it involves all of us here and any of our members who have access to metal and metal working skills. I'm looking at you Terry, but if anyone else wants to join in it would be awesome.
So, I went looking for materials in my shop and I'm running short on stuff to make these with, and I'm getting frustrated because we can all picture other ideas to try, but I don't have the materials and/or skills to make them. But, they are small parts, easily shipped. So, if anyone out there wants to fab up some pieces to try, I'd be happy to test them. Shilo, I know you are too far away, but for example, a longer piece that fit into the port, or went all the way through it with a slot pointing up into the port. Or Terry, your idea about the two 45s on the tube. Anyway, it's just an idea, but if anyone is into it, I'll pay shipping. Let me know.
Here's dimensions of v4: Inlet channel is 2.14"w x 1.25" h x 18.5"L. Pre-Port tube is 9"H (firebox floor to top) x 1.25"I.D. Slot is .25"x8".
Awesome collaborative challenge, Matt! I don't have access to any tube that shape, but could have some partially fabbed/ welded to that size, SS or mild, maybe even out of aluminzed steel, too, at the transformer factory at which I work. I'd love to make a stock in flow tube w/ interchangeable upright tubes of various slot/ hole patterns.... Something else to think about, along with getting my batch box built.... Hey, how about a trade- shipping cost of the parts for you coming to Va to help me ! I will chip in on your design anyway I can, Eric VW
Sterling work Matt. I love the flat Eff% & CO lines on your graphs!
Could your 8" bench/flue be contributing to the low stack temperatures? The gases wont be flowing as fast. Plus you've added your extension on recently. Slower speed = more heat transfer = lower stack temperature.
Could you clarify your comment on the sizing. Are you talking about v3? v4 doesn't have the second tube, and is larger. It is I.D. 2.25"x1.25" for a csa of 2.8"sq. which is exactly what I was going for. 10% of a 6" system csa.
Matt, Maybe I wasn't completely clear about the duct sizes. Your horizontal rectangle duct of V4 is adequate but not more than that. The vertical round duct of V4 is way too small as compared to the slot.
To be precise: the ductwork should integral be at least 50% larger than the slot. That is what I've found out 6 years ago during the rocket/bell project. To sum up what you have there: the horizontal duct is 2.8 sq in, the round vertical tube is 1.22 sq in. and the slot is 2 sq in. In order to use a slot of 2 sq in. all the ductwork upstream of that should be at least 3 sq in. csa. Maybe 2.8 is also good enough, I don't know because I've only tried a tube and a slot which were equal sized plus a tube which was about 1.7 the size of the slot. The differences were huge, according to the Testo.
It's not clear whether the slot in V4 is the only opening, but I'm inclined to think it isn't. But as it is, the round tube combined with that slot isn't very effective in my opinion.
Post by matthewwalker on Nov 22, 2014 10:32:59 GMT -8
Thank you everyone.
Andy, thanks so much for the kudos! I totally think the larger flue run is contributing to the low stack temp. Lazy movement through the bench. I'm also noticing a huge reduction in fuel use, apparently. There are a lot of factors contributing to that, but I feel like this is a really, really good heater, and slow movement through the mass appears to be a large part of that.
Terry! Awesome man, I had hoped so, knowing what your resources are. I'm totally open to whatever design ideas, that's kinda the whole point. Get some other brains in on this thing. I have the Testo, and a test bed in my home that needs heat. It's a good opportunity for all of us, I think. Here's some dimensions:
Door opening is 3"w x 2.5"h....There is a sliding damper, above the opening, that allows different height parts to be used there. I use plaster to seal the sides if the part is under 3" w.
Port starts at the floor. Roughly 2.25"w x 4"l before it enters the riser chamber, but it's pretty sloppy since I just cast this sucker right onto my J core.
Yep, so far I've been working towards that 2.8"sq. number, although as Peter illustrates above I'm not quite there. I think your range is good, but as mentioned, I'm game to try whatever you want to try. One thing I've learned with this Testo is that it's really tough to guess what's happening. These things behave strangely, that's for sure.
A couple notes on how I'm operating right now. So, Peter's original design is a true rocket, going full tilt. What I'm doing now is different, and I'm trying to live with it to see if I'm on the right path from an operating/livability stand point. So far, I think it's a good thing. But, it is very different. So, operating goes very similar to a normal new wood stove or masonry heater. I light the fire at the opening to the port, then load lots of small kindling, then larger fuel on top/behind the kindling charge. Very much like a top down masonry heater starting charge laid on it's side.
I set the sliding damper open above the secondary inlet. That configures the thing into almost original design parameters, a little less air. Currently it's roughly 3"sq. primary and then the secondary, which is changing but roughly 2.5"sq. or so. I run it like that for about 10 minutes, and it roars like the original. At that point, depending on how I loaded the fuel and how dry it is, the whole thing should be starting to take off and I'll be right on the edge of over fuel situation, where O2 goes low and it blows smoke. The goal is to get the secondary tube hot, the port hot, and the afterburner well established. At that 10 minute mark if things are raging, I'll slide that damper and then it's almost all secondary, a little slot for window air wash and some leaks. I think less than 1"sq. primary. If I get it right, the port lights up like the sun, as you can see in that video above, while the firebox goes pretty dark and the wood just gasses. If I get it wrong, the secondary port burner struggles, and the thing smokes. It takes a bit of fiddling, but I'm starting to get it down to where it's a simple operation. Once everything is hot, the afterburner is unstoppable, and I think a lot of it is due to the incoming secondary air coming in through red hot steel buried in the coal bed. This stove consumes CO much farther out into the cycle than any of my other rockets have done, thus the flat line.
So, I'm bringing this up so anyone with ideas can think about those things. Right now, my tube is fairly heavy gauge steel. It takes the full 10 minutes to even get started and then it's right on the line. It also burns CO way out in the cycle, so there's two sides to that.
Also, the air amount...I'm trying currently to go down to no primary, which means there needs to be enough secondary air to give me headroom to handle the big offgas events like when the fuel drops or the whole pile ignites when it burns back to the primary leaks. Peter, that headroom is why O2 levels are high, I think. I can tune it to run with lower O2 when it's in cruise mode, but that means that the big offgas events overpower it and it spikes. So, somewhere in there is a balance. You can also go the other direction, which is what the original design does. It blows off a lot of the gas with the primary so there is less to consume at the secondary stage, thus it is more able to handle big gas events. The trade off there is rate. Once you are tuned to burn full out, you gotta burn full out. So, there's some things to consider. I'm currently chasing that long flat line, although I don't think I'm trying to create an all night wood stove. We still have mass, and I still believe in that, I'm just trying to deliver the heat to it in a steady state over a good amount of time from a reasonable load.
So, yeah, I don't know what I'm doing, but those are some thoughts.
Huh.. So basically, you're working with a part time gasifier, part time rocket stove. How do you handle the coaling stage?
There is a gasifier that is worth looking at. The build is sort of complex but the results are fantastic. It's called the "world stove" It's unfortunate (for us) that they're trying to make a market out of their stove, so the plans aren't readily available. There are videos on youtube that show the thing being assembled and used. A LOT can be gleaned from them.
I don't know that it will help, the trick to the worldstove is the way it handles air, which seems relevant somehow. My intuition talking.
Post by matthewwalker on Nov 22, 2014 11:38:54 GMT -8
Yeah, it's a good question Donkey. I'm sorting it out, but it would seem in normal use that I do two or three batches on top of one another, and then there is one long coaling stage on the way out. The Testo shows a long steady climb in CO during that stage, but no huge spike. It does coal for a while, and if I'm in a hurry to reload I'll go back to rocket mode by opening the primary and hitting the coals. I haven't noticed a huge difference in smoke production from the chimney over when I would let my J go out, since I would effectively do the same thing there when heading out to work or whatever. Let it burn down and cover it, still a fairly long coaling stage, although nowhere near the same size coal bed.
I dunno how it will all pan out, like, is that a particularly dirty aspect of this? I don't know. My experience with the Testo and the full out burners is the short duration of extremely clean burn was bookended by periods of dirty burn as well, whether the ratio is way different here, I don't know. I need to set up the machine and do a full start to finish run and find out. I'm still able to easily switch back to the standard configuration as well, so I can do back to back and find out. I'm planning on tuning this a bit more, then going back to that and doing some more testing.
OK, port is also 9" tall? 2.25X9=20.25. Which is 71% riser.
Just to throw some thoughts around.
You definitely need primary air. Oxygen is needed to heat the fuel for out gassing.
If the fuel gets too hot, over gassing occurs and extra secondary is needed to complete the burn. We can control this over gassing by cutting back on the primary. This would lengthen the burn time, which is what you seem to be experiencing. CO spikes should also be minimized with a smaller primary because of less heat in the fuel box.
Your dirty window is also a sign of a small primary. The gasses in the batch box are heavy with volatiles(tar-creosote) and will stick to everything. They should burn away once you get into the coaling stage. The coaling stage can only happen with primary air. This stage with it's high radiation, is where most of the heat damage occurs to our metal.
Donkey, I closely watched those stoves a few years back. I made a few that were natural draft. Very remarkable to see the out gassing under the flame bubble. They are low on heat since they are only burning volatiles.
It is a true gasifier in that it produces charcoal. For our purposes, there is a lot of BTU's in that coal and we need to use them!
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