peat
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Post by peat on Jan 9, 2012 3:52:50 GMT -8
Hello folks, I am planning on building a portable rocket stove as part of a demonstration field kitchen to be transported by bike trailer. It will be used in conjunction with a hay box oven to get people thinking about alternative, low energy methods of food preperation. I have built low weight portable rocket stoves before, but for this one I would like to incorporate a verticle feed. This is a design element I really like and it would allow me to focus on other things without having to worry about checking the fuel to often. However, I am worried that without a chimney creating draw, there is a danger of the flames travelling up the sticks in the feed tube. I have searched quite extensively for a similar design and am beginning to think that the reason that I have failed to find one is... because this problem is very real and that the design will not work. However, I did come across one mention of this kind of stove, but the description is brief and the picture unclear, but it does suggest that it can work. www.greenstone.org/greenstone3/nzdl;jsessionid=8ABF0FAFA1CB44E22D596B3923A065AC?a=d&d=HASH01f40b5df83cbd6767a78dbd.15&c=cdl&sib=1&dt=&ec=&et=&p.a=b&p.s=ClassifierBrowse&p.sa=Does anyone have any experience building this kind of stove, or can offer any alternative options? Any advice would be greatly appreciated. Thanks Pete |
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Post by Donkey on Jan 9, 2012 8:27:35 GMT -8
Well, I build 'em in the yard out of heavy stuff.. Otherwise, they will be essentially the same. The heat riser needs to be a little taller than your standard Aprovecho cook stove. That's pretty much it. You gotta remember that the Aprovecho cooking rocket was designed, not just to be an efficient fuel user, but to ALSO be culturally appropriate to the target audience. They discovered fairly early on that regardless of how well the thing works, it just won't get used if it doesn't fit into the cultural practices of the people that you introduce it to. The things are very short because in the places where it was introduced, the people traditionally cook sitting on the ground at a 3-stone fire. But look, we're trying to introduce this technology back to the west.. We HAVE to make them culturally appropriate or they will NEVER reach wide acceptance... Sure, people will say " wow, that's cool, I want one." but when you leave it to 'em, the novelty will quickly wear off. If the thing isn't comfortable to use (culturally comfortable and "convenient"), it's just gonna end up in the garage gathering dust with the rest of the junk. Ok, rant over..  So, you'll need a taller heat riser. It should be roughly 3 times as high as the top of the feed box, and the burn tunnel should be as short as possible. This is gonna have it's pluses and it's minuses.. The minus is that (I think) some of the careful proportions that Aprovecho came up with may go out the window. The gap around the pot will remain the same, but it will now be higher off the flame itself, which will change how much heat gets into the pot, how fast. It's gonna effect the efficiency (of getting heat to the food) a little. The up side is that the cooking surface will be higher, which is more culturally appropriate for folks in the west who cook standing up. I'd accentuate, maybe even putting the whole thing on legs to get the pot up at waist height. Seems like a good trade off, shave off a tiny bit of efficiency to gain wide acceptance in the target audience.  In short... It's gonna work great AND people will love it! |
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Post by Donkey on Jan 9, 2012 8:30:23 GMT -8
Umm... Since there's no barrel (this ain't a mass heater) you can probably get away with a shorter heat riser than I said above.. Maybe twice as high (as the feed) instead of three times..
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Post by grizbach on Jan 9, 2012 10:56:13 GMT -8
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peat
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Post by peat on Jan 9, 2012 15:32:00 GMT -8
Great. thanks for the encouragement guys! i shall keep you updated on my progress.
Cheers
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peat
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Post by peat on Jan 10, 2012 3:20:43 GMT -8
With any vertical feed tube, flame up is possible. I build a shield around the entrance to minimise this. What do you mean by a shield? And should the bottom of the burn tunnel be slightly higher than base of the feed box for ash to gather? Cheers |
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Post by Deleted on Jan 10, 2012 8:19:29 GMT -8
Attachment shows my Paperclaycrete experiment.
The blackening is mostly from my eperiment with oil burning.
After all the time it hast still not completely dried in the winter here.
It has virtualy no burn tunnel.
A tunnel would create more turbulence and ensure better combustion
The fire comes only out of the feed if it is windy, but allways only for a very short time.
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Post by grizbach on Jan 10, 2012 8:33:43 GMT -8
Peat, My shields are a 3 sided vertical channel placed on the feed box with the open side away from the barrel. Think of it as a continuation of the feed box with an open door towards the front.
Without this "open door" this shield would act like a chimney pulling against the draw.
No need to have different floor heights. Although on my RMH, I have a grate on the bottom of my feed box that leeds to a catch bin for the coals/ash.
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Post by grizbach on Jan 10, 2012 8:40:35 GMT -8
Karl, Isn't oil nasty stuff? I have put an oil drip on mine also and was amazed how dirty the ash became. I thought that the efficent burn of the rocket would clean it up.
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Post by Deleted on Jan 10, 2012 9:18:06 GMT -8
I have placed a metal pot in the feed with just a bit oil soaked cat litter at the pot's bottom, for testing. Once the pot becomes hot enough the oil burns nicely and does not produce a lot of smoke. An extremely simple pot design is described here by Bruce Woodford. journeytoforever.org/biofuel_library/ethanol_motherearth/me8.htmlHere in Europe I own only a part of an 18 parties house. I can not perform very extensive tests on my balcony because of the neighbours. Anyway so far I am pleaced with my tests. In a few month we will visit our house on the philipines again, where I have enough space, coconut stuff to burn and plenty of time. |
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peat
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Post by peat on Feb 1, 2012 15:15:06 GMT -8
Been doing lots of thinking about the stove and designing, but am still uncertain about what to use for the innards. It's a toss up between weight and livespan. I want it to last. So... flue pipe is too thin right? i'm thinking around 2mm thick wall, steel tubing. My problem with this is that I can't weld, and would have to pay someone to do this as well as buying the pipe, and I want to keep costs to a minimum (not an insurmountable barrier, I know).
grizbach - what did you use for the internal tubing? I have been concidering using refractory cement, as you can buy small amounts for relatively cheap, and I could mold it to what ever shape I want. Would this be a light option? Can it survive the bumps and scrapes of being on the road? should I add something too the mix to reinforce it?
Cheers guys
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Post by grizbach on Feb 1, 2012 16:43:27 GMT -8
Hello Peat,
Both my RMH and grill have a 1mm crs heat riser that I have welded.
I'm on my third year heating with the RMH. There are always rust flakes on the riser when I do my cleaning about twice a season. Unless I come up with another design I plan on running it untill the pearlite pours out.
When I built the grill I coated all the guts with furnace cement slip to try to prevent rust since it stays outside year around. It looked good for a couple months, kinda rusty now. Since I have the outer shell galvanized, the appearance is holding up.
I haven't used refractory yet. I'm sure I will though.
Terry
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peat
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Post by peat on Feb 2, 2012 2:16:10 GMT -8
Cheers for the reply. So you use 1mm on you RMH and its survived. Thats encouraging. Then i could certainly get away with it for my creation.
Thanks
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peat
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Post by peat on Feb 2, 2012 3:10:18 GMT -8
I have been concidering using refractory cement, as you can buy small amounts for relatively cheap Actually I taken that back. I can buy fire cement for cheap... Can only buy huge amounts of refractory... could I use ordinary fire cement reinforced with steel mesh?... |
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