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Post by ronyon on Nov 16, 2013 19:28:39 GMT -8
What happens when you make the firebox of a batch rocket "too big"? Why doesn't the same thing happen to a pocket rocket? Or does it? Does a pocket rocket feed have the problems that a long feed on a J tube had(smoke back, fire in the tube)? If not, why not?
Also, a pocket rockets stack isn't usually insulated, is it? So how does it do the rockety thing?
The reasons for my questions is a fear that the precise measurements of a batch box will be tough to reproduce without welding or using a castible form. And yet the consensus seems to be that a batch box is less finicky than a J. Furthermore it is said that a big J is less finicky than a small one. ... Lastly , the pocket rocket seems to have a super long feed that is generally larger in diameter than the stack.
So It seems like a pocket rocket might be the simplest/cheapest rocket for me to build and learn from yet there are some principles at work in It that seem at odds with other rockets. If I can understand what Is going on maybe I can use some of these exceptions when I build stoves.
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Post by peterberg on Nov 17, 2013 1:19:54 GMT -8
A batch box rocket is actually a tunnel. The ratios between the firebox width and height on one hand and the firebox and gate on the other are fairly critical. Lengthening of the firebox can be done without much ill effect. When the batch box is properly made, running it is very easy. It is capable of devouring much larger wood as compared to the J-tube.
Don't know much about pocket rockets, never built one.
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Post by Donkey on Nov 17, 2013 9:13:05 GMT -8
Pocket rockets are NOT rocket stoves proper.. They have some features in common. They are fun demonstration stoves, and get extremely hot, but pour a HUGE portion of heat right out the chimney. Like other low mass stoves, they tend to run either too hot or not at all and when they go out, they go cold. Also, they get SO hot that the barrels (that they are made of) don't last very long.
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Post by ronyon on Nov 18, 2013 17:37:40 GMT -8
Thank you for your replies! So it would seem that a pocket rocket with an insulated stack and a barrel/bell would in fact qualify as a rocket stove proper. How ever the short life of the barrel makes for a poor design. Something like this shows a simple way to line a drum with refractory in order to increase the durability. Donkey, these stoves seem to have rather long feed tubes, that are larger in diameter than their stack . In a J tube of similar proportions this could cause reverse draft. Does it do the same problem occur with a pocket rocket? I am inquiring about this because on the face of it, this isn't an issue, and thus the pocket rocket design could be a great way to use larger, longer fuel. Peterburg, is there a limit on how short the firebox can be? I want my firebox to fit mostly inside the same enclosure as the heat riser, so shortening the firebox will be useful. On a different note, discussion of the P-channel often notes that secondary air introduced from beneath does not work. The cooking rockets that are cast out of Portland and insulation use a flat plate in the lower portion of their "L" to form an air channel, and rebar as a grate. I would incorporate the grate into the plate itself, if i choose to build an "L" but I thought I would ask, have you built simple consistent cross section"L" rockets? If so, what where the drawbacks that led you to the fire siphon and the firebox that is higher than it is wide? I am asking because I am pursuing simplicity of construction, and a simple L has that. If the drawbacks are not too sever, I might go down that road. Also, I am thinking I am not the only one with these questions, and perhaps we could make a FAQ: "Why build it this way and not that". Or something like that. You have done so much work, and yet the kind of peiople who are attracted to these DIY stoves , will also be filled with "why's?" as well as "how's?".
Thanks again for sharing you knowlegde!
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Post by woodburner on Nov 18, 2013 17:46:47 GMT -8
A batch box rocket is actually a tunnel. The ratios between the firebox width and height on one hand and the firebox and gate on the other are fairly critical. Lengthening of the firebox can be done without much ill effect. When the batch box is properly made, running it is very easy. It is capable of devouring much larger wood as compared to the J-tube. . Is there a topic that deals with the design of the batch firebox?
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Post by pinhead on Nov 19, 2013 6:54:56 GMT -8
A batch box rocket is actually a tunnel. The ratios between the firebox width and height on one hand and the firebox and gate on the other are fairly critical. Lengthening of the firebox can be done without much ill effect. When the batch box is properly made, running it is very easy. It is capable of devouring much larger wood as compared to the J-tube. . Is there a topic that deals with the design of the batch firebox? Yes. Adventures with a Horizontal Feed.
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Post by Donkey on Nov 19, 2013 7:51:40 GMT -8
Thank you for your replies! So it would seem that a pocket rocket with an insulated stack and a barrel/bell would in fact qualify as a rocket stove proper. How ever the short life of the barrel makes for a poor design. Something like this shows a simple way to line a drum with refractory in order to increase the durability. Donkey, these stoves seem to have rather long feed tubes, that are larger in diameter than their stack . In a J tube of similar proportions this could cause reverse draft. Does it do the same problem occur with a pocket rocket? I am inquiring about this because on the face of it, this isn't an issue, and thus the pocket rocket design could be a great way to use larger, longer fuel. Pocket rockets blast their heat directly to the sky.. Insulate the chimney, put a barrel/bell over it and all that, you will VERY quickly find yourself with the same rules as a regular J-style rocket stove. A wider, taller feed won't work so well anymore. Each design change introduces it's own compromises. The rebar grate isn't the way to go on those.. The wood should sit on a shelf that does NOT allow air to get to the wood until just below the heat riser. In this way you have control over the wood for cooking. Remember that the original L stove was designed for places with serious wood shortages, where the women have to hike miles to find wood for every meal. With these stoves, the hike must only be braved once a day instead of 3. The fire on those stoves should be tiny, intense and concentrated. Any wood that is not directly under the heat riser should NOT be burning. The disadvantage with using an L stove to heat is that you will be there shoving the wood up into the fire every minuet or so. they don't scale up as well as one would like, when you do, to work properly, you get something like the batch box design. My advice.. Try building one of the tried and true models of rocket stove FIRST. Get it right, outside someplace safe, THEN you can attempt to modify it and/or move it into your house.
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Post by ronyon on Nov 22, 2013 18:28:29 GMT -8
Good advice as always. I do plan on building a "conventional " rocket but I am already noodling about about what I want as a permanent installation. The grate I was referring to in the cookstoves is located only under the riser.
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Post by ringoism on Dec 9, 2013 10:03:34 GMT -8
Thank you for your replies! So it would seem that a pocket rocket with an insulated stack and a barrel/bell would in fact qualify as a rocket stove proper. How ever the short life of the barrel makes for a poor design. Something like this shows a simple way to line a drum with refractory in order to increase the durability. In our part of the Himalayas, they use pocket-rockets for domestic water heating: Instead of a simple outer skin, they've got a water-jacket, with an out-spout that flows when unheated water is poured in the inlet. Made entirely of very thin gauge galvanized sheet, with no welding (only crimping and a bit of sealant in a couple spots) and they last for years, by nature of the temperature limitations of water, I guess. Of course what the others have said is right, much of the heat goes out the stack - but still a lot more efficient (and fast) than heating your water in a pot over an open fire (and they do roar like other rocket stoves). -Eric
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Post by Daryl on Aug 19, 2014 5:15:57 GMT -8
Thank you for your replies! So it would seem that a pocket rocket with an insulated stack and a barrel/bell would in fact qualify as a rocket stove proper. How ever the short life of the barrel makes for a poor design. Something like this shows a simple way to line a drum with refractory in order to increase the durability. In our part of the Himalayas, they use pocket-rockets for domestic water heating: Instead of a simple outer skin, they've got a water-jacket, with an out-spout that flows when unheated water is poured in the inlet. Made entirely of very thin gauge galvanized sheet, with no welding (only crimping and a bit of sealant in a couple spots) and they last for years, by nature of the temperature limitations of water, I guess. Of course what the others have said is right, much of the heat goes out the stack - but still a lot more efficient (and fast) than heating your water in a pot over an open fire (and they do roar like other rocket stoves). -Eric Looks like someone has the same idea for a water jacket: Only posting this as an example. I know there are faults to the build.
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