Homemade Downdraft Gassifier Wood Buring Stove

Ah, good… I was afraid I had missed something in my understanding of gassifying stoves.

No problems then…

Yes, I too am grateful for the explaination. :)

I just built and tested a stove based on Ryan’s model. Very impressive–clearly burning the wood gas. Very hot, very efficient, no smoke. The flame was not blue, but was jetting from the holes in the inner can.

I wonder what the burn pattern would be if the holes in the inner were smaller.

On the bottom of the inner can, I just cut big holes will a razor knife for ventilation.

As always, thanks to all for the great ideas and techniques. The forums on this site are a treasure.

thanks for mentioning the absence of smoke when using the stove, I remember this now that someone said it, I guess I just did not notice while using it, Another great advantage to this design.

I completed the final peice of my stove last night, the pot stand.

I am not sure If it will hold up in high heat I would test it, but it has been raining for the past 4 days and is supossed to continue for the rest of the week

I made it from an aluminum film canister

here is a picture on top of the stove

It is removable

and rolls up to fit in the stove

I also made a change in the fire grate, I made larger holes in the bottom of the can

and am using a thin titanium stake to suport the inner can to make more room for air to flow

here are a few more pics.

the final dimensions are 4″X4.75″

If anybody has the time and cash to burn…

Try making a similar stove out of a double walled titanium mug. Try starting with Snow Peak’s 21fl.oz (4.4oz) or 15.8fl.oz (3.5 oz) double walled tall stackable cups (http://www.snowpeak.com/gears/tw-stackablecupspage.htm).
—smaller seems impracticable. These are starting weights. Some material will be taken away, and a little added-so they should be close to a finished weight. The price (sans labor) is still less than a Bushbuddy.

1. Remove the handle assembly (if not starting with stackable cup)
2. Cut the majority out of the outer bottom–but leave the lip for strength.
3. Cut the inner bottom out about 1/2-3/4″ from the bottom and replace with lightweight SS hardware mesh, or weave your own out of SS wire (or simply pepper the intact bottom with 3/16″ holes, ala R. Faulkner’s stove).
4. On the outside, Drill 3/8″ holes 1/4″ from the bottom all the way around w/ 3/8″ gap (experiment for best dimensions)
5. On the inside, drill 1/4″ holes all the way around with 1/8″ gaps (or whatever makes it an even fit–make a template) about 3/4″ from the top.
6. For a pot stand, try fashioning some apparatus with titanium wire that will sit over the lip.

From what I’ve read by those who have designed such stoves, that the size of the holes and their placement matters a lot for the performance of a particular sized stove. I don’t know the formulas, but you could search http://www.repp.org’s stove discussion list for assistance, or write to Tom Reed or Paul Anderson.

One could practice with tin cans to get the best setup, then transfer the dimensions to the expensive titanium. There are also many cheaper stainless steel double walled cups that could serve to practice on.

Just an idea–any takers?

Andrew,

I’ve considered a similar design myself out of the doublewall stackable cups as they don’t have any handles to remove. However I believe that working the holes into the inner wall will be trickey.

I have also considered using the Ti Single Cup (II) (one of each) as I believe it would be easier to work the inner and outer cans seperately and these two should (I haven’t actually seen them in real life) stack with plenty of annular space for air movement.

has anyone considered or tried making a wood gassifier with a beer can outer and a small steel can inner to save on weight. I am thinking of using a heineken can for the outer. It might be hard to find a lightweight steel can in the right dimensions for the inner though. How hot does can the outer get on the stoves made so far? Would it be hot enough to warp/melt aluminium?

The outer can would certainly not get hot enough to melt/burn aluminum–it may char if touching the inner can at the top. Ask Ryan F. how his aluminum pot stand worked–that should let us know if it is a servicable material. ALW

Cheers for the reply Andrew. Ill have to give it a go as soon as I get through this beer.

I am also thinking of using mesh for the top half of the inner to save on weight, which will extend past the top to act as a pot support. But I will see how hot the outer gets first-that might be pushing it too far. Especially as the most available fuel for me is Eucalyptus (In Australia) which burns very hot.

The minimal research I’ve done into wood stoves showed that they threw small amounts of spark into the air immediately surrounding the stove. However, seeing as how the models we are particularly discussing are gassifier stoves my information may not be correct.

I tried tin can versions, but found them not easy to light. Then, along came the littlbug (note there is no "e"). I found it easier to light the fire on the ground without the can or chimney. As soon as it gets going put the stove on top. Design your sove without a bottom. If you do not want to do that and have your stove portable while lit, or not scarring the ground, I would suggest designing the stove so the the match can be held underneath the tinder. The flame has a larger area of tinder to ignite. If building a fire on the ground, just dig out a small trench with two fingers, making it easy to get the match underneath. Use the lid of your pot to fan the flames.
http://outdoors.webshots.com/album/556839194qbaYfz
Have you seen the chimneys used to light charcoal for grill cooking. There is a space for tinder (newspaper) to be lit underneath the charcoal. The charcoal sits on a small grate a few inches above the bottom where there are also vent holes. BTW for tinder look for the lowest dead branches on evergreens, like hemlocks. A handful of the smallest twigs on these branches, still attached to the tree, ignite easily.

The real Bush Buddy is a highly refined stainless steal stove that weighs 6.5 oz., and burns wood cleanly and efficiently. By analyzing its structure, we can re-create its effectiveness from cans. I've written an article on how to do it for the next issue of Wilderness Way Magazine: http://www.wwmag.net/features.htm . Meanwhile, here are a couple images of it:
Parts: Outer Can: 4" dia x 4.75"; Inner Can: 3.5" dia.x cut height with large bottom hole with four each tabs bent: up and down; Ash Tray: 3" dia x cut height with 4 side-pressure tabs; Half-inch hardware cloth grate inserted into slits for corners; Pot-holder/windscreen: 4" dia x 2" tall, turns over and slides between inner and outer walls for travel, and all fits into billy-can (4.25" dia x cut height to fit) opened with seal-cutter so lid can be re-used. Air-flow spaces all at least a quarter inch. Ashes build up an inch before blocking flow; revive by shaking. Bottom doesn't get too hot for raw-wood surface like picnic table. Easily moved while burning with pliers of multi-tool. Releases almost no sparks even in moderate breeze.

Yes I have done it using a 2 litre aluminium japanese beer can as pot and outer jacket The printing discoloured but the aluminium never got close to melting. see this thread. http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=8025&disable_pagination=1
My pot windshield and stove all nest and weigh a total of 200 gram

I've simplified and lightened my design with a single 4" x 6" can.
A grate doesn't have to be continuous. These lower draft hole flaps, bent in, hold up most of the wood, allowing coals and ashes to drop into solid-bottom ash tray, so heated air comes up under wood for a clean burn. Same size vents above let flames lick pot on their way out. Ample door (2 1/4" wide by 1 3/4" tall) allows feeding of large wood plus more air exchange.
Single piece is strong, light, leaves no trace, no parts to lose or abuse. Burns fast and clean. And of course it needs a small aluminum wind-screen if used in an unprotected place, to prevent embers from getting blown away by a freak wind.

I;m glad they did away with the terminology of Down Draft to describe the stove. Notice that most of the authors sold their own version of the stove. The double wall thing is hype. The wick glows red hot and acts as a catalytic burner of a type to consume all gasses going up and out just as in the common kerosene space heaters.
.

Okay, now I'm just confused.

So the whole Double-wall Downdraft concept is just an illusion? Are they not any better than Hobo Stoves?

I was about to start making one until I read Dan's post on this and the other thread: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=8025&disable_pagination=1

Is best stove to have the main fire raised above the coals collecting at the bottom and anything other than that is just superfluous (such as a double wall)?

Here is a piece of information in regards to the woodgass stoves:

I was happy to see an updated description/terminology being used in the quoted preface (quote)

RICE HUSK

GAS STOVE

HANDBOOK

Alexis T. Belonio

With “Preface” by Paul S. Anderson

PREFACE

The importance of this “Handbook” and the work of Engr. Alexis

Belonio should not be underestimated. I have been given the honor to write

this Preface, and my intent is to illustrate the importance of this work.

The search for technology for clean combustion of low-value dry

biomass in small stoves suitable for residential cooking has been ongoing

for hundreds, if not thousands, of years. One relatively new technology

was identified and initiated in 1985 by Dr. Thomas B. Reed. He originally

called it “Inverted DownDraft” (IDD) gasification, but recently we have also

called it “Top-Lit UpDraft” (T-LUD) gasification, a name that more clearly

denotes what is actually happening in this combustion technology. The terms

“gasifier” and “gasification” refer to having any type of combustible gases

from dry biomass created distinctly separate from the combustion of

those gases, even if the separation is only a few millimeters and/or milliseconds.

Developments and adaptations of Dr. Reed’s IDD or T-LUD

technology during the past twenty years have been slow, mainly without

commercial products, but discussed and shown occasionally as a

combustion curiosity on every inhabited continent.(end quote)

I believe the double wall to be insignificant when it comes to our little backpacking size stoves. I removed the double wall from my Zip Stove and tests showed it heated 2 cups of water faster than with a double wall. 3 seperate tests per stove were done on the same day, same conditions. A unmodified Zip against my modified one. Same amount of fuel by weight(clothes pins/kiln dried=)) The single wall Zip was more efficient. Both zips had their fan setting secured on the half throttle setting while stoves were under test.

Edited to add link to thread Modified Sierra Zip Stove

Zelph,
I'm with you on the wood gas issue: Single wall is just as efficient as double wall, all other factors being equal, including outside size. In my somewhat primitive tests the single-wall was also lighter, held more fuel, lighted and powered up quicker, created less soot and could store more stuff inside.

As far as I could tell, the largest performance gain in stoves using the same can size came from elevating the fuel to improve oxygenation. In the single wall, this was achieved with a hardware cloth grate.

I just made my own hobo wood stove out of a small coffee can. Half way through my first test with it I remembered that some metals give off toxic gas when put next to or into fire. Would I have to worry about toxic fumes from my hobo stove?

Vick,

What you and Dan don't seem to understand is that a fire in a can has no sex appeal. Add an extra wall and give it a cool (if wholly inaccurate) name and you have something you can talk about all day in forums and get a lot of wows on the trail :) Maybe if they put a small dish antenna on the side of single walled stoves they'd have more appeal.

H

Herman, I think you are absolutely right. =)

Everyone should go back to making the double walled downdraft gassifiers. Add a few bells and whistles. Remote piezo ignition systems, .001 Titanium throughout, auto ash dump when stove is folded for storage. =)

Now you're back to square one and alot more sex appeal. It's what our society is all about, it's what sells product. Put more holes in it to make it look "tactical" Vary the shape of the holes to make it have more "sex Appeal"

> Vary the shape of the holes to make it have more "sex Appeal"
Heart shapes?

Cheers

Yes, heart shapes for the female DIY's in the forum if any. Hole quantities can be 38 on top. 22 in center and 30 on bottom. Shape the stove in an hour glass form. I'm sure the "Stuff Sack" could be made in an interesting fashion.

I'm sure the "old School" can make it happen. ;)

some real nice creations, first one in this thread looks real professional. ive simply called them chimney stoves after being basically a little chimney or similar to the chimney charcoal starter. in essence you have a small wood burning fire where heat is directed straight up and air flow is provided through holes in containers wall.

i considered building one of my own but opted for a built model that disassembled and can be nested inside of a pot. its the littlbug and works very well. i dont think ive seen a diy hiker make one quite like that yet but it makes a lot of sense due to packing space.

due to limitations at certain hiking trails/shelters im now having to build an alcohol stove so smoky the bear wont eat me.