Rocket stove





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  1. #1
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    Default Rocket stove

    Once again, an interesting concept on the cooking outdoors theme.

    Rocket stoves in whatever configuration are known to use very little fuel and handy when large quantities are not available or like in our current situation where one can't just burn bags and bags of wood or charcoal. The smaller metal version one can run on dry leaves, twigs or if you have, even newspaper. You are obviously going to battle to cook a 5 hour lamb potjie but it can be done if you have to.

    So mostly these stoves are used to boil water or make a quick pan fried meal but the larger ones can be used as a "braai" if needed but it will mostly be used to fry in a pan, or any fllat surface as the heat is rather intricate to get constant.

    Once one fiddles with rocket stoves it becomes evident, real quickly how important it is for a fire to breathe, which apllies to any fire regardless if it is in a pizza oven or your Campmaster fold up braai or in a hole on the beach.

    Some of the ones I have made had small cavities, but they worked and I have cooked on them many times.
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  3. #2
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    Default Re: Rocket stove

    As my tandoor oven scheme with the facebricks didn't work, I had them spare and packed together a larger rocket stove this morning. This is the base.
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  5. #3
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    Default Re: Rocket stove

    Placed some foil to close the cavities in the feeding chamber, if using solid bricks this won't be required.
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  7. #4
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    Default Re: Rocket stove

    As mentioned, airflow is critical with these things so aome way of suspending the fuel off the floor really helps. I modified a toeknyp rooster for the pizza oven already so that was used with some more tunung to fit into the fire chamber.
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    Default Re: Rocket stove

    Grid is placed and there ia enough space to insert the fuel once the fire is burning.
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    Default Re: Rocket stove

    About the fuel, this is about the largest one must use, I have found anything larger kills the draft and then it smokes.

    Another plus point of the rocket stove is once burning, it smokes a hell of a lot less than an open fire as the gasses in the wood are heated much quicker and burns faster.
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    Default Re: Rocket stove

    Yep, I knew you were going to extend the inlet into a tunnel. Are you going to cover the tunnel?

    I'm going to replicate this. I have welded fencing mesh that I can use as a coal floor spacer.
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    Default Re: Rocket stove

    Once the desired height is reached, not sure what it should be and there will surely be a ratio and formula somewhere but using Eyeball Mk1 I reckon this will do. Some pavers on top, leaving gaps for the air in the sides and a grid goes on top where one will be cooking on.

    And we have a rocket stove. Named so due to the rocket/ whoosh like sound it makes when revving.
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    Default Re: Rocket stove

    Crank her up!

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    Default Re: Rocket stove

    So Riaan what are you braaing/cooking in/on that Spoetnik today?
    We can't change the wind but we can set our sails

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    Default Re: Rocket stove

    Quote Originally Posted by Francois Theron View Post
    So Riaan what are you braaing/cooking in/on that Spoetnik today?
    Doing a pan fried brunch firstly. Still thinking what to do supper with, my choices now are rather varied.

    But I have a scheme for the rocket stove for supper so it will probably do double duty today
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  22. #12
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    Default Re: Rocket stove

    Quote Originally Posted by andrewdjulyan View Post
    Crank her up!
    Patience Andries, ek soek nog my bierbeker vir die rum
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  24. #13
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    Default Re: Rocket stove

    http://kulkulfarmbali.com/how-to-bui...endly-cooking/
    http://theselfsufficientliving.com/d...-small-spaces/
    rocket stove plans pdf
    https://www.google.com/search?q=rock...w=1366&bih=632

    We have been using a slightly different measurement convention in our workshops, based on the difficulty of repeatedly measuring center-to-center dimensions on a muddy build site.
    We measure the inside dimensions of each channel from edge to edge.

    We measure the largest dimension, brick-to-brick, in each case:
    - feed tube full height (the largest piece of wood that would fit in it with a lid sliding over the top),
    - burn tunnel length from the farthest wall of feed tube to the farthest wall of heat riser (longest stroke you might take with an ash shovel; this floor length includes the total width of feed, heat riser, and the bridge between them),
    - heat riser height from burn tunnel floor to upper rim of heat riser. (drop a tape measure into the inside of the heat riser.)

    Based on this measurement standard, we like a ratio of
    feed = 1, tunnel = 1.5, heat riser > or = 3+.
    In other words, the heat riser is three times as tall as the feed, and at least twice as tall as the full length of the burn tunnel.
    For 8" heaters this gives for example a 16" feed, 24" burn tunnel, 48"+ heat riser.

    In terms of Peter's center-line measurements, my proportions would correspond to a 12.5" feed, 17" burn tunnel, and 44.5" heat riser, or 1: 1.36 : 3.56.
    I certainly don't object to making the heat riser taller: a full 4 would be a height of 50 inches above center line, or 53.5 inches above the floor, which also works great with slightly stronger draft for an 8" system. So Peter's method adds 5.5 inches to my method in this case.

    I find subtracting half of a 7" (or in some cases 7.5", etc) width to be a pain in the neck, however, and am likely to stick with my edge to edge method.

    For 6" heaters: we often make a burn tunnel 20 to 24" long, and the heat riser is correspondingly 40 to 48" tall (or slightly taller) - measured floor to edge.
    The difference of 1/2" or so from square to round channels does not greatly affect any of these measurements; in fact we sometimes place a round heat riser section on top of a square U-shaped brick firebox with good results.

    Based on the OP calling the burn tunnel 7 inches, I would guess he's measuring the bridge only (shortest physical distance between the closest inside edge of the feed, and the closest inside part of the heat riser.) This bridge is often between 7" and 10" in most of our designs; depends mainly on what size barrel/bell is being connected over the heat riser, to avoid the barrel lapping over the feed. (We like to leave about 3" to 4" between bell and feed, to allow replacement of the first bridge brick if needed, and stacking a taller feed outside the barrel if appropriate.)

    With this bridge length, assuming a true 6" round system and the feed isn't too tall,

    - by my method the burn tunnel is about 21" long (including that 8" section, a 6" feed, and 7" bridge) so the heat riser needs to be at least 42" tall (from the floor of the burn tunnel area upward). The feed could be up to 14" tall, measured from the floor of the burn tunnel. If the heat riser is offset from the 8" section, we might consider the burn tunnel as only 20" long, wanting a 40" heat riser, and the feed could be about 13" tall. Again, these are floor-to-lip and full-floor measurements.

    - by Peter's method as given above, the burn tunnel is effectively 13" long (7" bridge plus two 3" halves of 6" ID tubes; I'm ignoring the 8" weird thing).
    Thus, the heat riser needs to be at least 29" tall (measured from the midpoint of the burn tunnel, and double its mid-flow length),
    and the feed no more than 6.5" tall above the midpoint line (an opening into the burn tunnel with a 3.5" lip, if you hooked the tape measure on the underside of the bridge and measured up to the feed lip).
    To make a feed that could hold wood over 12" long, in a 6" diameter system, which by Peter's method is a 9" feed height,
    you'd need a heat riser at least 36" tall (above the burn tunnel midline), and the theoretical burn tunnel length would be 18" (from midpoint to midpoint). I'm not sure whether his system would call for also extending the burn tunnel to fully double the feed height, or if the feed and burn tunnel can be shorter (in my experience making them shorter is entirely tolerable).

    This system with a feed that holds 12" fuel wood, with the heat riser alone proportioned according to my understanding of Peter's system, would be measured 12" : 20" : 39" by my edge-to-edge measurement method; I would add another inch to that heat riser by my method (double the burn tunnel and triple the feed), making it at least 40" measured from the burn tunnel floor to heat riser lip.
    or 12" : 24" : 39" if the burn tunnel was lengthened to Peter's formula; in that case, I'd add 9" to make it 12: 24: 48 (at least double the burn tunnel length and triple the feed; the feed could be lengthened another 4" as well, if desired).

    In case any two methods or suggestions disagree, I highly recommend taking the taller heat riser of the two.

    I'm also not sure what the 8" chamber is doing back in between the burn tunnel and heat riser. We have seen some poor results in prototyping from size bumps, and generally prefer to keep the same cross-sectional area throughout. It seems to be the easiest configuration that burns clean.

    Hope that helps.
    I agree that using different measurement references makes things complicated, but I don't like the idea of revising my books and plans to make them more difficult to measure and use!

    I can see the centerline calculations as useful for theoretical flame-length guesswork, but when building a brick or pipe system on site, it's annoying to have to calculate each measurement, and marks don't last. (The brickwork usually involves courses in two different orientations, so there isn't even a one-brick-shy-of-the-bottom reference in reality.)

    I think Leslie and Donkey have privately allowed they see the benefit of using this edge-to-edge measurement method, so I thought I'd put in another plug here. If it doesn't mess up Peter's calculations too much, perhaps we can use my measurement method. If it does, perhaps we can give each standard a shorthand name, or put some diagrams up or something.

    Here's a diagram of an existing 6" heater we built in 2008, reportedly still in use (we lived with it for about 3 years before moving, and it heated reliably during that time). The measurements we use are marked in blue.


    I've been away from these forums for too long, so hope this post fits the general style of discourse here. Please point me toward any dedicated discussion of the 'standard' if I should be posting there instead of hijacking this one.
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  26. #14
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    Default Re: Rocket stove

    And a virreo. Jelo, see the reason for the longer tunnel, compared to the pic you posted. Although not critical, it just works better this way.

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  28. #15
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    Default Re: Rocket stove

    ek smaak dit stukkend
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    Default Re: Rocket stove

    Also, do NOT use your fingers to feed already burning wood deeper into the oven, the back end is super hot as the steam escapes there. You will burn badly, so use another piece of wood or your favourite braai tongs.
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  32. #17
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    Default Re: Rocket stove

    building a real turbo stove. mix the clay with grass or other fibre clippings
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    Last edited by bertus; 2020/04/06 at 02:49 PM.

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  34. #18
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    Default Re: Rocket stove

    more
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  36. #19
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    Default Re: Rocket stove

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  38. #20
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    Default Re: Rocket stove

    Using two pieces of threaded rod, a potjie can be suspended in the hole. I had thought the heat will be difficult to maintain evenly but it works brilliantly. Feed a piece of wood now and again to keep the flames going and it sorts itself out.

    Did notice that the pot battles to get super hot unless one feeds lots of wood.
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