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Rocket Stove Design

 
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Id like to get some input from any of you rocket stove building gurus on a stove Im building. Im trying to determine on where to place the fuel feed tube. I have looked up a million diff plans but they all seem to be different. I have 2 photos here the two diff ways I have seen them built. I also have the option of cutting the feed tube to go centered into the 90 also but, dont have a picture of that.

Another question is would it be a waste of time to build a grate in the bottom horizontal tube. I plan to add an air regulator on the bottom tube and a full cover on the feed tube.

TY

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rocket stove design
rocket stove design
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rocket stove design
rocket stove design
 
gardener
Posts: 2435
Location: latitude 47 N.W. montana zone 6A
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cat pig rocket stoves
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Hi Scott; Welcome to Permies and the wonderful world of rocket science!

Of your two photo's I think the design in the second photo will work better. The design of the first photo would disrupt the flow in your riser.
Next I will mention that your metal will spall out after a short time, if your stove reaches rocket temps.Until then it will work great.
A grate in the bottom is common for those trying to use pellets, not really needed when using wood.

Do you have a copy of the RMH builders guide ?
What are your plans for this rocket?
What is the rest of your build going to be?
Our friendly crew is eagerly awaiting your questions.
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Our friendly crew of rocket scientist's eagerly await helping you
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These guys are getting your success party ready
 
Scott Myers
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Thank you for the warm welcome and reply. I have been a spectator here for some time now and figured it was about time to join. Ill update my profile soon.

I was leaning toward the second myself. The plans for this build is more of a back up way to cook food in case of an emergency. Plus the 1/4 steel tube was free from our scrap dumpster at work. ( Im a fitter / welder )

I have not bought the book. Currently putting all my extra money into being prepared for emergency situations and to get some land to live the permaculture dream on. Ill prob pick it up when ever I get around to making a rocket mass heater.

I will post a photo and let you know how it works soon as I finish it.

TY

 
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I would put the diagonal feed tube as in this video: https://www.youtube.com/watch?v=3_UXKX1Y1Fw

The video shows how the feed tube is diagonally meeting directly the 90 degree bend, rather than have it shifted back, or shifted up the chimney as your choices.
 
pollinator
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building woodworking rocket stoves
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Hi Scott,  One thing that I've heard with making an angled feed tube is that the wood doesn't smoothly feed very well. As a kid I remember a slide at the park that on some days you would just stop half way down due to too much friction. Not sure about pellets.
If you do decide to go with the angle, let us know how it goes and good luck with the rest of your build.  
 
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When you get a rocket stove "rocketing", the heat is enough for metal to start spalling.  Where do those tiny bits of metal have the potential of winding up?  In the food you were cooking.

The only way I would ever use metal for a rocket stove is if the heat was fed into a self-contained metal cook top, usually protected with firebrick of some kind.  The gases heat the cook top before circulating around and exiting through a flue.  Having made the mistakes with metal, I now know to stick to high-temp masonry products (firebrick or ceramic fiber/fiberboard) for the burn chamber and riser.  There's nothing more frustrating that building a rocket "stove", only to find out it won't get hot enough to cook the way you'd hoped.  The best way I've found (by doing a lot of things wrong) is to build a properly sealed and insulated masonry core...that's when things get HOT!  
 
gardener
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I would say that unless you want a traveling stove, a masonry J-tube or L-tube will work best and last longest. If you build a masonry unit where you can use it, you may find yourself using it regularly for outdoor (under shelter) cooking. This would get you proficient with using the rocket stove, as well as saving expense using your gas or electric stove. The chance of a SHTF catastrophe is pretty remote, but being frugal and learning everyday is real preparedness.
 
Glenn Herbert
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If you must build your stove out of steel, I would suggest making the feed vertical instead of angled. That way the wood will be guaranteed to drop all the way to the bottom, and the fire will encounter two right angles on its path, making it more turbulent and aiding fuel/air mixing. The angled design has the fire at the bottom of the riser, so it encounters only one turbulence-generating angle.

I note that you have your riser significantly longer than your feed tube, which is good as it will allow the riser to firmly establish the correct draft instead of wanting to burn back up the feed.
 
Ted Butrell
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Glenn Herbert wrote:If you must build your stove out of steel, I would suggest making the feed vertical instead of angled. That way the wood will be guaranteed to drop all the way to the bottom, and the fire will encounter two right angles on its path, making it more turbulent and aiding fuel/air mixing. The angled design has the fire at the bottom of the riser, so it encounters only one turbulence-generating angle.

I note that you have your riser significantly longer than your feed tube, which is good as it will allow the riser to firmly establish the correct draft instead of wanting to burn back up the feed.



The angled design meets directly at the chimney, so the angle feed and chimney are really two chimneys.  In seeing the video of two candles in a box with two chimneys above, one candle is calm, and the other flame is turbulent, so the angle design shares a chimney, so it would have to be a mix of turbulent and calmness.  If the fire would somehow "shrink" or be microscopic (still a normal rocket, but the particles at small scales dominate), then having a level entrance, and angled entrance, and a vertical chimney, the angled entrance would travel faster because a grid of squares, the diagonal direction on graph paper of a square is longer than either edge of the square, so diagonal directions travel faster since they have to travel a further "distance", but it would only work if something were added like a catalyst that would cause tiny sized particle movement.

The point would be that the chimney being longer would normally have air flowing up it, but you could tune it so there's complete stillness of movement up the chimney because the diagonal feed would travel faster, air inside would be still.  But the one thing I remember about that candle video is that there was no entrance but two chimneys, so initially air is being used up by the two candles, and then air flows down one chimney, and the other chimney air flows up (even if both chimneys are the same length because of variations).  Once again I say that a triangular chimney is involved, because I remember the time I had a triangular chimney, it was difficult for air to go up the chimney, but it still burned.

Edit: I would say that a triangular chimney would work smoothly if it has a diagonal feed going directly diagonal into the chimney, because the diagonal feed would make it easier for air to go up the chimney now.  I think you would also need a level entrance as well, because the triangular main chimney acts like the restriction.
 
Glenn Herbert
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The angled feed tube would only be a chimney if there were free air flow in the bottom horizontal tube and the feed were uncapped. Because of the proportions of the stoves shown, this could happen, but would never be the intended operation. If the bottom opening were unrestricted, both feed and riser would act as chimneys and air would rise up both.

Don't try to conflate the candle experiment with the stove; there is no reason why there would be a "combined calm and turbulent" area at the junction of the feed and riser. That is one area, not two, and it has its own characteristics.

"diagonal directions travel faster since they have to travel a further "distance""
Only if it is specified that the horizontal flow gets from start to end in the same time as the diagonal flow, which is not at all necessarily the case. The air will flow at a speed through each path according to the friction per foot in it, and if they are identical in cross section, flow will be the same speed for the same length path. For a longer diagonal path, there is more length to add friction, so the flow will actually be a bit slower, as both paths will end up with the same total friction.

The "vertical chimney" (riser) will always have greater natural draft than the lower, angled feed tube, and will always take more exhaust flow if both are unrestricted. The candle case is irrelevant to the stove, because there is no bottom entrance there as there is in the stove. Their behavior is not comparable.
 
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