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Post by peterberg on Sept 7, 2008 9:03:39 GMT -8
Hmmm. The advantage I'm seeing with the down-feed style woodbox is that the flame is held in a constant place. The fuel and the air are always at an optimum place for a clean burn. That's true, Donkey. But there is a downside on this, if you choose to call it this way. It do work best with hard wood. But softwood is much cheaper and often to come by for free, even in a crowded nation as the Netherlands. So I am working on a soft-wood burn chamber. I imagine that in your stove, the fire has room to meander about... Seek it's own path, as it were.. Does there tend to be unburned pieces laying about after things go out? Or does it pretty well burn everything, no fuss, no muss? The fire does meander about, yes. In the sense that it is growing, and on a certain point in time the whole batch is burning. And the thing do tend to leave unburned charcoal, specifically around the perimeter of the grid. I tried to solve that with triangle pieces of firebrick. Do work better now. Today I've been evaluating all graphs of the test runs, and found out that lowering the bottom of the fire chamber wasn't such a good idea after all. So I changed it back again.
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Post by Donkey on Sept 8, 2008 20:45:00 GMT -8
Yes, that's interesting.. I kinda saw a picture in my mind of the firebox, much as the image above.. Good point on the hard/soft woods.. Softwood does tend to allow the fire to creep up and out sometimes.
In the image, have the wedge pieces been through a burn cycle? I'm noticing the pattern of carbon blacking.. You can see where the hottest parts of the fire are, there is no black. I imagine that the pyro-gas (smoke, etc) swirls about a little in the firebox before finding the burn tunnel and heat riser. Would it be helpful to raise the back tunnel up towards the top of the box?? Or bring the top down somewhat? Is the extra room at the top necessary? Also, what if the grate were ONLY the size of the system (6" or 8" or whatever) and moved to the front, directly below the glass? Would it help to make an all under-air system burn properly?
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Post by chronictom on Sept 8, 2008 22:01:52 GMT -8
It would be easy to find out, just use a couple of pieces of sheet metal over the grate as it is and move them around to find out if positioning and/or size matter
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Post by peterberg on Sept 9, 2008 0:51:02 GMT -8
Questions, questions. But it'll keep me thinking about it.
The wedges have been through years of burn cycles, but not in this firebox. What the picture shows is the situation right after the change. The white areas are looking smaller, but are mostly covered by brick. On the sides that's 6 inches.
The flames indeed wander around a bit before the rocket warms up, after that they are running nearly horizontally to the exit hole. The pattern is now nearly the same, with more white area and still 2" black at the ceiling. The exit hole is white all around and inside. Interestingly, there's a quite large white patch (about 8") in the middle of the ceiling.
Probably it would improve things to move the exit up 2", and have rounded corners everywhere at the upper half of the chamber. But that's too far fetched at the moment.
Where the grate is, there's no charcoal left behind. Move the grate, and you'll get it again. But it is a good suggestion and I'll try that. In case it do create a positive effect I'll let you know.
In a definitive version, the air would come in directly at bottom level in front of the glass. But it will be over air in that case, coming in as low as possible. The air that do come in at the moment is very much less than the size of the system, about half of it.
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Post by peterberg on Sept 9, 2008 11:32:44 GMT -8
OK, tried the closed firebox floor. Sloped sides, 2" wide gap just behind the door like Donkey suggested, left and right a small tunnel under the triangle pieces ending in the corners at the back. Total air intake is still not the same as system size, but quite nearly so. Next thing planned are two steel pipes running through the tunnels, with a corner piece to vertical and ending left and right of the stoke hole. Maybe that'll do the trick for better oxygen provision. After the second refill the whole system choked itself resulting in a dirty burn. Opening the loading door a small gap for 2 minutes provided a solution. Ash and charcoal leftovers are clearly visible, blackening is a bit less, but still the same pattern. The rocket "elbow" is all white inside. It seems I am getting there, albeit slowly.
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Post by chronictom on Sept 10, 2008 18:03:15 GMT -8
You know the old cast iron water radiators they used to use?
Stay with one bell above the stove. Put a couple radiotors side by side in the bell with baffles in between them so the exhaust passes though each of them before exiting, add some lines to a storage tank mounted above the bell and I think you would have an excellent system.
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Post by chronictom on Sept 10, 2008 18:06:16 GMT -8
Why do you have it so the start of the exit from the fire box is raised up? If it was running straight from the floor back, it would eliminate a turbulence point in behind the current lip, and get the burn running smoother no?
Did any of that make sense?? lol
Also, what do you mean by softwoods?
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Post by Donkey on Sept 10, 2008 18:41:20 GMT -8
Funny, I have been thinking the same of the top of the stove. I'd like to see the upper corners tapered somewhat like what Peter's done with the bottom. Also, perhaps move the top down. Keeping it off the floor does exclude charcoal, fallen fuel and other chunky bits. I see too much potential to foul the tube and choke it off. Better to keep it off the floor at least a bit. ??
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Post by chronictom on Sept 10, 2008 18:49:39 GMT -8
I think it comes back to this is a firebox as opposed to a tube. With the tube, it's all a straight burn (even with the elbows), all the gasses are kept right in the main burn area with no place for them to escape to... With the box, they have room to swirl and move about.
It seems to me that it is a better arrangement to keep the burn area all as tight and smooth as possible, get everything that can be burnt, burnt and the heat then funneled into the bell, which is where some turbulence (to keep the surfaces bathed in heat) is good.
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Post by Donkey on Sept 10, 2008 18:59:35 GMT -8
Good point. He's trying solve the tendency for rocket stoves to be fiddly, making them undesirable to some folks. You just gotta be a certain kinda bloke to like frutzing with the fire all'a time. Actually, you do want a certain amount of turbulence in the burn tunnel. The danger of smoothing too much being laminar flow conditions which disallow good fuel/air mix. I think I've mentioned otherwhere on these boards that I've been fooling with turbulence generators.. I have been pleasantly surprised at the difference!
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Post by chronictom on Sept 10, 2008 19:12:10 GMT -8
with the firebox, make it so the smoke and gasses get into the tube as smoothly as possible, then hitting a turbulence generator while still at temp, but after being 'focused'.
The reason I said that earlier and this now, is that if the smoke is wandering around the firebox before exiting to where the gases burn, it is losing some of its heat immediately to the walls no, which may be effecting the final burn for it all.
I'll leave that as that and go find that other thread about tg's
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Post by peterberg on Sept 11, 2008 0:34:04 GMT -8
Tom, I don't want to build a central heating system. Neither a forced air system. But if you do like to give it a try, I am all ears.
Donkey answered it already, a pile of wood in front of the entrance of the burn tunnel is no good at all. The flames in the tunnel will be starved of oxygen and that's what everyone is trying to avoid. I've tried it already a week ago. Lifted the floor an extra 2" and stacked the wood with lots of air space between it in front of the hole. The resulting burn was very, very dirty, beyond the reach of my gas analyzer, with a matching low efficiency.
To get a good combustion, three factors are important. Time, temperature and turbulence. The twist in the burn tunnel is providing a lot of turbulence. That'll allow for good mixing of air and woodgas. At the same time it'll lengthen the burn tunnel, giving the flames a longer "stay" in the hottest part. Actually, maybe in a later iteration I'll make the twist a bit deeper. And rise the entrance a bit.
Poplar, fir, pine, hemlock etc. are all softwoods. Oak, beech and the like are hardwoods. I've been making furniture for 20 years, in Dutch all the names are very familiar to me. In English they're entirely different.
Donkey, the closed floor and air entrance under and in front of the loading door wouldn't work. At first it did look good, but after 15 minutes the flames did block the entrance of oxygen in the burn tunnel, CO went sky high and O2 to the lowest point I've ever seen. With the pipes I've mentioned before installed to provide some air to the entrance didn't work either. So I'm going back to over air, a very little bit under air and a grid. This combination's providing the best results according to the graphs.
And you're right. I'm trying to work to a point where the stove is less fiddly.
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Post by chronictom on Sept 11, 2008 6:20:32 GMT -8
I know what hard and soft woods are peter, I meant what do you have access to over there....
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Post by peterberg on Sept 11, 2008 8:28:56 GMT -8
Sorry, Tom. Must be my sketchy knowledge of everyday English. The majority of the firewood I can lay my hands on is from conifers. Sometimes poplar or willow. All the wood I'm burning during wintertime is coming from a large glass trading company. A part of the glass is delivered in wooden crates, for the company this is waste material. So the wood I am using comes from all over Europe, sometimes from Canada, Russia, Japan (Asahi Glass, very large mirrors!) or Singapore. Sometimes I do flatter myself with the thought of having a true international fire.
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Post by chronictom on Sept 11, 2008 13:36:16 GMT -8
That's sorta cool, I once had a piece of this purplish type hardwood from brazil given to me from some pallet off heavy equipment... you can end up with cool things that way.
I must admit though, when it comes to firewood, I much prefer the idea of the 40 acres of trees we have around our house, which includes a mix of 47 diffierent species of tree... It seems odd to hear someone say they only have access to softwoods, which is why it caught my attention.
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