3.3oz downdraft gassifier wood stove

[Michael Skwarczek]

Recognize the can?

Pretty, no?

Ignore the cockeye'd screen/support, it was adopted from this 5.5oz steel design…

I'd been working on the steel version, which has been field tested and burned at least 2 dozen times. It performs well, but could do better with some modifications. I realized, while testing the stove, that you should be able to use an aluminum outer wall. The Heine can is the obvious choice, Fosters are too weak. I just needed a proper steel can for the interior. Any 15oz steel can should have done the trick. I initially chose a "Del Monte Mandarin Oranges" for its smooth wall, and used this in my first design but the gassification was stymied; I think by the limited clearance between the two walls. Next, I came across "Zhena's Gypsy Tea" and had a perfect fit, more clearance, and voila. BUT, don't run out and grab a can, I'm having a bad time with its baked enamel surface giving off throat-closing toxic fumes on every burn. I've tried to scrape the sides with a wirewheel angle grinder twice, and while it looks like most of the surface is gone, I'm smelling sporadic fumes. BUT, just today I found a new can, Asparagus Tips. Slightly smaller diameter than the tea can, but the same height as the Heine. We'll see how the combo works with my next build.

My final thought: while the 3.3oz is a great step for UL packs, I'm not impressed with its packability when combined with the ti-600; it sits 1.5" higher. Meanwhile the 5.5oz version packs cleanly; perfectly flush with the top lip of the pot. There's a lot to be said for that.

-Michael

EDIT: Is there a Ti pot that's 3.5" to 4" in dia. and 6" tall? That would nicely hold the Heine stove.

[Adam Kilpatrick]

Michael,

first of all, nice stove, I'm glad someone has finally taken the plunge with using an aluminium can such as the heine for an outer on a DDG stove.

The dimensions you have mentioned (3.5" diam) mean a pot at about 945mL. The Firelight 1100 (which is out of stock atm anyway) is only 4.25" high. Firelight 1300 is even shorter.

Thats just an example, but I doubt you'll have much luck finding such a tall Ti pot. The vargo pots are much broader than that, as are the AGG pots (even their 2Qt pot isnt that tall).

Snowpeak trek 900 is 5.1" high, so is getting closer.

If only a Heine can came out now that just so happened to be slightly larger so that you could fit your stove in it :)

Another option, whether it would work or not is another matter, is to downsize the stove again, using different materials, eg pepsi can-outer and god-knows-what inner. That would fit inside either your Ti-600 or a Heine can. Might have difficulties with combustion though.

Good luck-looking forward to hearing results,

Adam

[Vick Hines]

Oh, my. That looks so good. Can you give more details? Crossection? I don't quite understand how this works.

[Michael Skwarczek]

Vic:

Check out these links for good descriptions of the DDG concept:

has anyone tried this wood burning stove?

Homemade Downdraft Gassifier Wood Buring Stove

And here's a great diagram from the first thread I linked:

Here's the parts of my build:

The inner wall slides in from the top where the lip of it catches on the cut opening in the Heine can bottom.

Adam:
Great suggestion. Here you go: Made from a steel can that's shorter than a Pepsi. Steel 'cause I had it laying around after some cyclone stoves, and it fit perfectly. True gassification. But we'll see if I can keep it going long enough to boil water.

[Steven Evans]

Michael,
That is really nice work. Very economical aswell. I was wondering though, if you reduce the interior dimensions that much, is it difficult to keep the fire going? ie, do you hve to feed it constantly, or does it burn for a while. I was playing around with some designs earlier this year but thought if the innner chamber became too small and narrow, it would become problematic. Any thoughts or results from testing?
Again, good stuff!
Steve

[Dave Heiss]

Michael,

I'm also impressed – nice work. Elegant in its simplicity! Have you done any tests to see (approximately) how long the burn is with a full load, and how tall the pot support needs to be for maximum efficiency and minimum smoke?

Also, your holes look clean. Are you using a drill, or a dremel tool, or something else to make the holes?

Thanks!

[Vick Hines]

Dang, that's nice. Dang, now I have to make one. Dang, I can't use it around here because gathering veggie matter is prohibited in state parks. Unless I carry wood in. Dang.

[Derek Goffin]

I made a similar stove But in England you cant get Henicans. I got an imported 2 litre Japanese aluminium beer can and turned the top 40% into an aluminium outer wall diameter 111mm and found an ordinary steel inner 100 mm diameter about 130mm high. I put a grate 25mm up. There are primary feedholes just under the grate and secondary air feed holes just below the top. The aluminium outer wall hangs onto the top edge of the steel inner. I use a 1lb treacle tin as the potstand. This nests into the rim of the lower steel can and locates the outer. I use the bottom of the Japanese can as a 1 litre cook pot (35 gram) With a large aluminium turkey bag as a windshield . The total weight including pot is 200 gram.
The flame pattern is just like that shown in this thread but I disagree with the posted diagram. The flames are formed when unburnt gases are driven off the fuel upward and reignite when preheated secondary air from the annular space between the inner and outer walls mixes with these gases to give renewed combustion. The wood does not give off fumes downward. hot air does not easily travel downward. I can prove this because in my stove the outer wall does not start until well above the primary feed holes which are the only potential path for fuel gases to get into the annular space as shown in the earlier diagram. I am certain that my stove, the bushbuddy and the stove on this thread work by upward gassification and recombustion with preheated secondary air. Either way they work well.

My stove has no bottom so it must be placed on a stone. the embers and ashes fall on the stone, the stone gets hot but it does not soot up or mark. If you wrap it in cloth afterwards it warms your sleeping bag on a cold might.

[Derek Goffin]

I forgot to say all these components nest into the 1 litre alu pot except the alu outer wall which with a slit in it slips over the outside to stiffen it.

[Adam Kilpatrick]

Michael,

impressive! I am on the lookout now for a suitable steel can for an inner for a pepsi-can outer DDG stove! (In Australia…)

I guess with a reduced inner volume fuel volume will be reduced, and you might have to add some more if you want to get it to a boil. Probably not that big a deal…its not like you are adding alcohol to an already burning alcohol stove!

Off I go to the supermarket, can hunting!

Adam

[Steven Sergeant]

This looked like an interesting project, and I wanted to try it myself, so I built one as well. I used it on a recent SUL trip to the Ventana Wilderness near California's Big Sur coast recently. (The pictures were taken at a trailhead campsite.)

The stove was made simply of parts of three cans and a bit of 1/2" hardware cloth. These particular bean cans were chosen because they stack; in other words, their bottom crimped lid is a smaller diameter than their upper crimped lid, and thus nests inside the rim of the top lid..

The tools used were a can opener, hand drill, Exacto knife, sheet metal shears, and needle-nosed pliers.

One can becomes the burn chamber. Both ends are cut out with the can opener. The other can is opened initially at the bottom to remove the beans, and then cut about 1/2" from the wider, top end with the sheet metal shears after starting from a drilled hole. The top 1/2" of the can, with the lid still intact, become the ash pan at the bottom of the stove, and the remaining bottom of the can becomes the pot stand and wind screen. The beer can is cut by repeated scoring with an Exacto knife to precisely fit the two cans inserted into each end. Holes were drilled for ports in the lower sides of the beer can and the upper sides of the burn chamber can, similar to the description above. The hardware cloth was attached to the bottom of the burn chamber by making 1/4" vertical snip in the bottom of the burn chamber can, and bending up triangles to crimp in place the wire.

Here's the stove, ready for a burn. The finished stove weighed 3.4 ounces. It's full of oak chips and found twigs, with a tiny (1/2" x 1/2" x 1/8") shaving of "Presto Log" on top as a starter.

Once the stove is lit, I wait for wood gassification to begin.

Then I put the pot on. In this test, it contains 16 fluid ounces of about 60 degree Fahrenheit water.
Even the slightest breeze seemed to diminish the efficiency of the stove. It worked much better when I added a more robust wind screen. (Note even more wood-gas burning in this shot, above.)

Finally, after solving the wind problem, and adding almost the same amount of wood that I originally loaded the chamber with, I got a rolling boil in under 11:00 minutes.

After the very first burn, the expansion and contraction of the cans made disassembly impossible without destroying the stove. After about 8 burns, the aluminum has become rather soft and I fear for the continued durability of the stove.

I agree with the other poster who said that the close distance between the two cans probably limited the wood-gas flow to the upper ports. But it did perform quite nicely cooking for 2 people over a weekend, and even for just 4 meals, saved total carry weight versus an alcohol stove, wind screen, fuel bottle, and fuel.

I'm thinking of trying the paint can stove in this thread next: http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/6402/index.html

[Joshua Mitchell]

got to get around to cutting up some cans soon…

[chris Mcfarland]

Derek,
when i first heard about this stove design i thought the downdraft part of this stove isn't necessarily movement of air so much as its thermal feedback from the flames above heating the fuel below?

on that same note I've found that if you angle the inlet holes on the top of the stove down and slightly spiraling the flame pattern becomes more stable and wind resistant as well as providing more thermal feedback to the fuel below. by cutting the holes to look like an inverted L and then pressing them from the inside into the cavity between the inner and outer wall, as opposed to drilling them

[Derek Goffin]

Chris,
I am sure there is thermal feedback from the flames I just wouldnt call it downdraught.
I tried a similar experiment with U shaped cuts and the tags pushed inward. I did get some spiral effect on the flame and that ought to give stability and better mixing. The 3 T's of combustion Time, Temperature and Turbulence. nonetheless I found it difficult to get a neat tag that did not snag on things in packing and went back to drilled holes. Perhaps your design is better. However If I had pushed my tags outward my system would not have nested for storage

[chris Mcfarland]

i used an ASIHI 1 liter can bottom half for the outer, and what was left of the top half wasn't suitable for a pot. it was first opened the conventional way and then consumed during the construction process, the beer, not the can:) so i got myself another can and made that into a pot. i nest mine the same way as you described, but i only bent the top tabs outward and the bottom tabs were bent inward to support the screen . the best of both worlds maybe? also it kinda looks like a giant alu pill when all is said and done.

[Derek Goffin]

Chris,
I am pleased to hear how similar your stove is. My pot was made from a 2 litre (ashai?) beer can The reason my stove did not nest with tags out was because I wrap my double folded turkey bag windscreen round the fire box can before I slip it into the Japanese beer 1 litre pot.
You are right, when the slitted secondary air jacket is on it does look like a big pill capsule.
Have you found a way to reduce the heat downwards from the ashes?

[chris Mcfarland]

are you talking about preventing it from making a fire scar? the inner fire chamber is made of a smooth sided stackable cocanut milk can. the top of these cans almost snap togther when they are stacked so i just cut the top off of another can, cut three legs into it and snap it onto the botom of my stove. when i nest it all togther, i can invert it onto the bace and the legs fit smothly around the fire box allowing me to also place my pot around the hole thing. im working on getting some photos up, but i dont have a camera, just my friends camera. waiting on him

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