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Post by rectifier on Apr 30, 2011 21:06:00 GMT -8
Hi guys, I've been building small stoves and gasifiers for years but never ventured into rocket territory before. So I'm wondering if the 'pocket rocket' design can help me out with an idea i'm working on. It's traditional to heat wall tents in Canada with airtight stoves. It's also traditional to have to stoke the stove in the middle of the night or wake up with icicles on your nose. Also they are heavy compared to a 5-gal bucket and a couple bits of stovepipe! Was wondering if the 'pocket rockets' use significantly less fuel than a traditional airtight, is it possible to throttle them back in any way, and how well they feed large hunks of wood. I like the vertical feed idea in that you could stuff in a big long log and hopefully burn it all night (can you? or will it eat wood too fast?) If they go out how are they for backdrafting... I still don't trust downdraft designs that much and like the sideways fuel magazine ideas a lot more like on Donkey's awesome stove. Could the 'pocket rocket' be done with a sideways magazine made of stovepipe? I am also thinking of a modified design more along the lines of a RMH where exhaust is pumped under the wall of the tent rather than through a heat-leaking stove jack hole. Like 'brett hunter' on this thread www.permies.com/bb/index.php?topic=2473.0 using a heat riser to build pressure in a pocket rocket type design. Then dig a trench under the tent wall and run the pipe under there and then up into a stack - i dunno about this idea but I might just test it and find out - it would only be about a 2' horizontal run. This is just kind of an up in the air idea, not too serious. Thanks guys |
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Post by Donkey on Apr 30, 2011 22:03:40 GMT -8
Hey, welcome to the boards..
Pocket rockets burn like the dickens. They eat small diameter wood and pump out the heat. Problem is, like all lightweight stoves, when the fire goes out it goes cold quick. Also, they channel an AMAZING amount of heat out the chimney. I see no way to avoid having to get up in the night to feed the things..
The down-draft design is crucial to pocket rockets, it keeps the wood in JUST the right place, channels just the right amount of air, and holds turbulence right at the junction between the two for good mixing. If the machine is missing one of those variables, it's just another barrel stove.
Once the chimney's hot on a pocket rocket, there's typically NO back-draft as long as the airflow doesn't get backed up. One of the flaws of the design is that coals and ash tend to pile up at the bottom, choking the machine. Usually stirring the wood, giving the barrel a bump or even tilting the thing a little will clear the blockage.
I'd be curious as to see someone trying to pipe the chimney down and around with a pocket rocket.. I don't know how well it would work, though I suppose it might do fine. Someone really aught to play with THAT question.
I don't actually consider pocket rockets to be proper "rocket stoves", though they share some features in common. The main thing missing is the insulated heat riser, which makes all the difference in standard rocket stove designs and sets it apart from others. Pocket's act pretty much like any other non-airtight, lightweight stove. Like yer grand-pops potbelly, as long as you shovel it in the thing goes like stink, when you stop it goes out and cold.
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Post by rectifier on May 1, 2011 11:51:33 GMT -8
Yeah, the pocket rockets actually resemble a downdraft gasifier more than a rocket stove when you look at the design closely.
However, that is what I was worried about. I suppose that if they pump out that much heat, in the morning one unlucky guy can re-fire it and get the place warm fast so everyone else can get dressed. However we will still be gathering just as much wood (or more) than the airtight since so much heat is going up the chimney.
The 'down and around' idea would have a tall stack on the outside to counter the downward section or else I see it backdrafting a lot. Also it would need a heat riser in the barrel, I think. Not really a pocket rocket anymore. Maybe I'll make a drawing as to what I am thinking about. In fact might as well build a proper rocket barrel and then pump it around a buried exhaust in the tent floor for the mass element. Not sure how well the ground would act as a heat reserve or if it would all conduct away into the cold ground.
Another idea I have been kicking around is to build a permanent RMH bench system out in the bush this summer that fits the tent. Then plop the tent down on top, set up our bedroll on the benches and we are staying warm all night during hunting season, with no holes in the tent and packing in no heating equipment too. The only concern is that it would all rust away in a couple seasons with exposure to the elements and infrequent use, and the benches would melt away in the rain.
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Post by Donkey on May 2, 2011 9:21:39 GMT -8
Another idea I have been kicking around is to build a permanent RMH bench system out in the bush this summer that fits the tent. Then plop the tent down on top, set up our bedroll on the benches and we are staying warm all night during hunting season, with no holes in the tent and packing in no heating equipment too. The only concern is that it would all rust away in a couple seasons with exposure to the elements and infrequent use, and the benches would melt away in the rain. I like this idea.. The cob would get buggered over time in the rain.. Perhaps the benches could be oiled with Linseed or some other hardening oil and waxed, like earthen floors. I've got a little patch of floor sample that I made and left out in the rain for several years. There's been no damage to the top of the patch thus far. Where the rain runs over the edge and underneath, where it's not been oiled, it's been worn away. It could also be lime plastered. Lime will protect the cob, it's breathable as well, so it shouldn't develop the kinds of problems that concrete stuccos and plasters have. |
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phil
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Post by phil on May 6, 2011 4:26:39 GMT -8
I've got a similar project in mind to heat a ~140 sq ft floor-less yurt, burying the stove pipe to use the ground underneath as thermal mass.
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Post by Donkey on May 6, 2011 7:25:34 GMT -8
Just remember that heat goes in all directions equally. (no heat doesn't rise, heated fluids do)
If you don't mind loosing half the heat to to the ground (lotsa places where that would be just fine) then just do it. Otherwise you should somehow insulate below.
There's been lots of talk in certain Natural Building circles that heating the ground could effectively lower the frost level around the house, reducing the need to dig extremely deep foundation trenches to get below frost line.. It could mean using MUCH more wood than you would otherwise. My climate is very mild, here your idea would work REALLY well.. A little overkill even. In Minnesota, It might be a different story.
How appropriate all this would be depends entirely on the conditions where you live.
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Post by rectifier on May 7, 2011 17:59:38 GMT -8
Here's a sketch I did up for a 5-gal bucket RMH concept. My scanner is at home and I won't be there for a long time, so here's a photo of the sketch  . It's 4", and I know there are issues with 4" RMH designs. But there is just not enough room in a 5 gallon pail for bigger pipe! Maybe I need a bigger pail. However the intent is not to pump the exhaust further than a couple feet horizontal before turning upwards into a vertical stack to get a lot of draw. If it worked well of course, we could run it across the tent and put our sleeping bags on top  It's a sort of hybrid rocket mainly focused on radiant heat at the expense of heat loss up the chimney - but hopefully less heat loss than the pocket rocket due to the downdraft section. The horizontal fuel magazine would just be a trench cut into the ground and covered over. Hopefully get a few hours burn time out of this at least. Also that's an easy way to get enough vertical for the heat riser as less than 25" is not recommended. I know you are using a horizontal magazine, Donkey - and there was success with one by someone else who built an underfloor heating system for a yurt (can't find the thread!). Why are they not generally recommended and are there some special considerations for them? |
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Post by rectifier on May 7, 2011 18:01:03 GMT -8
Maybe this time my photo will work? The photo is small size wise but for some reason appears huge when clicked on?
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Post by Donkey on May 10, 2011 23:29:36 GMT -8
Here's a sketch I did up for a 5-gal bucket RMH concept. My scanner is at home and I won't be there for a long time, so here's a photo of the sketch . Yer image is WAY too big. It doesn't need to be much more than 400 pixels tall or so. For Internet applications, web browsers and such show 'em pixel for pixel.. One dot on the picture equals one dot on yer screen.. Average screen resolution is something like 1024 X 768 or there abouts and you want yer image comfortably smaller than that. Your image will end up around 30 or 50 K bytes on disk. Well if you use it like an Aprovecho style stove, they more often end up being more fiddly than the vertical feed as you gotta push the wood in as it burns. The vertical feed tends to keep the wood in the optimum combustion spot automatically, horizontal feeds not so much. I think I've got that problem mainly licked.. It should be adequately described on my "home stove" thread. |
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Post by rectifier on May 12, 2011 16:49:04 GMT -8
Sorry about the huge photo. I put my camera on 'basic' to keep the size down for dialup users but didn't think of the pixel size. Most forums I have posted photos on before did some sort of server-side scaling so that it displayed a reasonable size on the thread.
Yes, on your home stove thread you mention it 'burning a whole load front to back' but you also mention pushing it to the front while burning. Which is it? Will it burn the whole load with no intervention or do you need to push it forward? And how long does the whole load last?
Also, re-reading that thread clarified the airflow for me, I think. No air enters the front two air tunnels, right - It is only supplied with air from the back of the magazine? And the pic with the door open, I assume you cannot operate like that for long as the draft past the wood is disrupted? Looks pretty though!
I think the underground magazine I drew would take quite a few firings to dry out enough to sustain a good burn. Maybe I should just bury a piece of pipe to put the wood in. It's annoying, I am trapped away from home at school and cannot build anything to test, all I can do is talk and draw.
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Post by Donkey on May 13, 2011 7:57:36 GMT -8
Sorry about the huge photo. I put my camera on 'basic' to keep the size down for dialup users but didn't think of the pixel size. Most forums I have posted photos on before did some sort of server-side scaling so that it displayed a reasonable size on the thread. Yes, on your home stove thread you mention it 'burning a whole load front to back' but you also mention pushing it to the front while burning. Which is it? Will it burn the whole load with no intervention or do you need to push it forward? And how long does the whole load last? It WILL burn completely untended, though I'm just not that sort of guy and it burns better with the wood pushed in.. A load seems to last a little more than an hour. That's right. The way I use the thing now, air ONLY comes in through the loading door, over the wood and into the fire. When it's running well, I can leave the door open surprisingly longer than I thought but it does interfere with proper draft. I can't recommend building it that way on purpose. Don't I know that one... You have my sympathies. |
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It's a sort of hybrid rocket mainly focused on radiant heat at the expense of heat loss up the chimney - but hopefully less heat loss than the pocket rocket due to the downdraft section.