Micro Rocket

[reardencode]

Well, I'm new to the forum, but discovered rocket mass heaters and rocket stoves just the other day and became intrigued.

I'm going to experiment with the small limits of the technology by attempting to produce a fully insulated 1" square (.87 inner width) rocket stove. The first design that I'm working on is built from 10" of 1" steel tubing (in two 5" pieces), 3" of 2" steel tubing and 2" of 1"x2" steel tubing, as well as 6"x9", 2 3.5"x2", 2"x2" and 4"x2" pieces of sheet steel, plus vermiculite for insulation.

This will give me a minimum of 1/2" of insulation surrounding the combustion chamber (more on some sides) and a full J shape for maximum turbulence.

Has anyone experimented with a non-pocket design this small?

I'll post pictures once I get my materials together today and start building.

[hpmer]

The smallest I've gone is 4", and then I went up to 6" and then 7". My experience was that the bigger the system, the better it worked, so I'll be interested in your results.

[reardencode]

Got my steel in and started the cutting and welding. I'm still a super newb at welding, so it's gonna be ugly, but I'll certainly update on my progress.

[Donkey]

There was a coffee rocket done in an office in Denmark (I believe) supposedly, it boiled water in no time flat.. I think it's in the book. Yep, here it is, 10 by 10 centimeters or 3.9 inches, and they say it boils a liter of water in 4 minuets.

Hmm...
Way back when, my first rocket stove was one of those little tin-can jobs with the wood ash insulation.. Boy, I thought it was somethin', I was impressed. Then I went and built (in quick succession) a six incher and an eight incher.. When I saw the eight incher run, my eyes popped!
I've since realized, that there's something more going on inside that doesn't scale below a certain thresh-hold.. A six inch rocket stove, built REALLY well, with short a bench run (if any) with every detail just so, and a little luck, CAN be something to behold. But when you get into eight inches and above, NOW yer talking sweetness!

There MUST be some kind of effect that is sustainable over a certain size, something that WON'T work below six inches (not that I've seen yet) and barely works AT six inches when ALL the conditions are right. Something OVER and ABOVE the standard model..

Cool project, by the way.
Lookin' forward to seeing your results.
Welcome to the board.

[reardencode]

Thanks!

I got the inner tube welded up yesterday and did some test fires in it. I definitely made the firebox too large and am going to have to either cut it down or put holes in it so that it doesn't counter the draw on the chimney.

I've also now started shaping the outer insulating box and will start welding on that today or tomorrow.

When playing with it w/o insulation yesterday, I was able to achieve a semi-rocket flame by blowing into it steadily (ie. the smoke cleared up and I saw flame in the chimney area), but I never got it to draw due to the aforementioned too tall firebox.

If this one doesn't work out I'll build a similar but 2" one or try extending the chimney section or more insulation or other experiments. I really want to produce a backpacking sized rocketstove just for the sheer ridiculous cool factor .

By the way, if you ever need steel pieces and don't have or want recycled, I'm going to plug onlinemetals.com -- they do custom cuts and ship quick. For me they're local too .

[rectifier]

Cooking rocket or heating rocket?

Not to discourage you, but I never had any luck with tiny stoves. Here's a couple of my experiences.

I experimented with a heating stove like this in the past. Down below can-sized heat risers, there appears to be no hope of achieving a downdraft heat exchanger (the barrel) as the heat riser will not build enough draft to push the exhaust down and out. Can sized (~3"?) is marginal and seems to depend on a siphoning effect that sometimes will start and sometimes will not. In small sizes it seems you want a horizontal feed, as you don't want anything countering the heat riser's draft.

Down in this size range, batch gasifiers seem to make more sense, like the MIDGE beer can gasifier (that's a great backpacking cook stove by the way) because the skinny wood that will fit into your rocket firebox will require a ridiculous feed rate to keep it burning properly. I once built a micro heating stove that used a 3" batch gasifier to achieve a 2 hour burn time at about 3000btu output. It had a downdraft heat exchanger section, and I considered that to be 'as small as it gets' for this type of stove. I put in way too much effort tuning that little guy, and in the end it turned out to not be practical to use due to loading issues.

Good luck! Micro-scale stoves are a whole different game.

[dkrocketstoves]

Hi interested in your experiments with small rocket stoves, I make and sell small rocket stoves if you look up DK rocket stoves there is some footage of them running on youtube.
But today I made an even smaller one from 30mm box as a model of the ones I sell and I fired it up and wow it works,
I think this is as small as I can go.love to see if there is a smaller one good luck.