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incognito
2008-09-27, 22:14
I recently did some test of a small woodburner to see if there was a significant difference between the single wall versus the double wall.

The stove is made of a quart can (outer) and a pint can (inner) there are some photos showing construction and holes.

The last 5 tests are given here. I performed 13 total test burns over a 2 day period. I tried to make everything equal.

New Chinese clothes pins were used in the initial testing. I ran out and started using American made in the last 5 tests.

Alcohol was used as tiner. Placed in a shallow pan under stove to ignite fuel. No wood was introduced once stove was ignited.

This was a test to see how the stove performed whole with double wall and then taken aprt and the inner can used as the single wall stove.

Test results are given at the end of videos.

American made clothes pins(30 per test) were used for all 5 tests. Only two tests were made with the single wall stove.

Keep in mind that the double wall stove was dis-assembled and the inner portion used as the single wall stove. The purpose of these tests were to show if there was any difference in the way the two performed.

I will give further details and show photos or videos of how the stoves were ignited. All things being equal ;)

The hour hand on the clock shows me which test was being performed in the series of 5. Two were single wall and three double wall


http://img.photobucket.com/albums/v228/obijiwa/sub%20one/th_TEST9WOODBURNER.jpg (http://smg.photobucket.com/albums/v228/obijiwa/sub%20one/?action=view&current=TEST9WOODBURNER.flv)

http://img.photobucket.com/albums/v228/obijiwa/sub%20one/th_TEST10WOODSTOVE.jpg (http://smg.photobucket.com/albums/v228/obijiwa/sub%20one/?action=view&current=TEST10WOODSTOVE.flv)

http://img.photobucket.com/albums/v228/obijiwa/sub%20one/th_TEST11REVISEDWOODBURNER.jpg (http://smg.photobucket.com/albums/v228/obijiwa/sub%20one/?action=view&current=TEST11REVISEDWOODBURNER.flv)

http://img.photobucket.com/albums/v228/obijiwa/sub%20one/th_TEST12WOODSTOVE.jpg (http://smg.photobucket.com/albums/v228/obijiwa/sub%20one/?action=view&current=TEST12WOODSTOVE.flv)

http://img.photobucket.com/albums/v228/obijiwa/sub%20one/th_TEST13WOODSTOVE.jpg (http://smg.photobucket.com/albums/v228/obijiwa/sub%20one/?action=view&current=TEST13WOODSTOVE.flv)

http://img.photobucket.com/albums/v228/obijiwa/sub%20one/th_2walledwoodburner102.jpg (http://img.photobucket.com/albums/v228/obijiwa/sub%20one/2walledwoodburner102.jpg) The tinder I used was 1/4 ounce denatured alcohol placed in this shallow pan which was located under the stove. The burning alcohol ignited the wood fuel through the holes located in the bottom of the inner can.


http://img.photobucket.com/albums/v228/obijiwa/sub%20one/th_2walledwoodburner101.jpg (http://img.photobucket.com/albums/v228/obijiwa/sub%20one/2walledwoodburner101.jpg) Holes in the bottom of the inner can where the burning alcohol ignited the fuel.


http://img.photobucket.com/albums/v228/obijiwa/sub%20one/th_2walledwoodburner100.jpg (http://img.photobucket.com/albums/v228/obijiwa/sub%20one/2walledwoodburner100.jpg) Inner can removed. A corrugated aluminum base with holes was attached at a height to match the position of it's previous placement in the double wall stove. Hole spacing was to match the outer can holes.


http://img.photobucket.com/albums/v228/obijiwa/sub%20one/th_2walledwoodburner099.jpg (http://img.photobucket.com/albums/v228/obijiwa/sub%20one/2walledwoodburner099.jpg) My first set of test burns of the single wall stove proved to be getting too much air. Fuel was being consumed too fast, not getting good temperature readings. This is the base that was attached to the bottom of the inner can. It was replaced with the corrugated aluminum base support.


http://img.photobucket.com/albums/v228/obijiwa/sub%20one/th_2walledwoodburner098.jpg (http://img.photobucket.com/albums/v228/obijiwa/sub%20one/2walledwoodburner098.jpg) This is a view of the bottom of the double wall stove showing the inner can recessed that provided room for the shallow pan that contained the 1/4 ounce of denatured alcohol that was used an my "tinder"

The amount of fuel and tinder remained constant throughout the tests.


Here is a recap of the tests performed:

1/4 ounce denatured alcohol was used as tinder.(in shallow pan under stove)

The super insulated double walled wood burner:

1st test burn = 190 degrees at 9 min.

2nd test burn = 186 degrees at 9 min.

3rd test burn = 154 degrees at 9 min.

Uninsulated double wall wood burner:

4th test burn = 180 degrees at 9 min.

5th test burn = 194 degrees at 9 min.

Single wall stove open base:

6th test burn = 172 degrees at 9 min.

7th test burn = 175 degrees at 9 min.

8th test burn = 210 degrees at 9 min. (American made hardwood clothes pins)


Single wall stove with new base added to replicate hole pattern of Outer can. American made clothes pins for fuel for next 5 tests.

9th test burn = 204 degrees at 8 min.

10th test burn = 188 degrees at 8 min.

Double wall stove:

11th test burn = 134 degrees at 8 min.

12th test burn = 180 degrees at 8 min.

13th test burn = 192 degrees at 8 min.

[b]The last 5 tests are significant. They give you a visual of what is taking place during the burning process and you are able see how the two stoves compare.

Conclusion:

No significant benefit to using a double wall stove. Why have the extra weight!!!!

More information is available if anyone is interested in this type of stuff.

.

Spock
2008-10-24, 15:36
I agree. I got similar results myself. In addition, a single-wall stove can hold more fuel. As a practical matter, IMHO, boiling time is less important that not having to interrupt things while you add fuel.

All things considered, single-wall wood burners are lighter in weight, have longer burn times (hold more fuel for the same-sized outer can) , are easier to light, can be used for storage, are easier to make.

incognito
2008-10-27, 19:19
Hi Spock, the same kind of test was performed on the Sierra Zip stove. I removed the inner wall and performed the tests in the same fashion. Results were the same also. Performed better without the double wall.

JAK
2008-11-06, 18:16
I tried insulating small hobo stoves to make them work better in winter but I think I agree now that it is better to simply make them a little bigger. Finding a convenient place to store them and still have them work well in winter can get tricky. Still working on it. I would like it all to fit in the bottle carriers on the sides of my pack, along with my mug and pot and still be able to carry my water or hot coffee in them while hiking. I want to come up with a metal pot first, with a lid so it can be used as a carrier but wide enough for soup and oatmeal and to clean out, and then design a stove to nest outside of it. Perhaps my stove on one side with one pot/carrier, and a cozy on the other side with the other pot/carrier. About 750ml would be big enough I think, if I had 2 of them.

Just Jeff
2008-11-16, 15:15
incognito - did you make your double-walled stoves downdraft gassifiers? They don't appear to be in the pictures but I can't really tell. That may change your results drastically for roughly the same weight.

incognito
2008-11-19, 14:46
incognito - did you make your double-walled stoves downdraft gassifiers? They don't appear to be in the pictures but I can't really tell. That may change your results drastically for roughly the same weight.

There is no such thing as a "downdraft gassifier" in the backpacking size stoves. Two kinds of hobo wood burners. The ones with a single wall and the ones with 2 walls. My tests have shown no significant difference in the two. It's best that you make your stoves the way you choose from seeing all the different designs here and other places on the net. Choose the one you like best. All wood burners gassify the wood to give us the heat needed to accomplish our mission.

The Garlington Stove is an interesting stove. Top lit, updraft stove. Try that one. It's a single wall. The history behind it is where all the stove makers get tangled up in their underwear. Just as Garlington had a hard time understanding it so does everyone else. Every one needs to read and re-read the history and even reread it again to fully understand what is going on with the design and theory. Read it, you'll find out where the "downdraft" part comes in and how the term has been misused in the backpacking world.

JAK
2008-11-21, 01:37
What's the best lightest stove platform over snow?

incognito
2008-11-21, 13:12
What's the best lightest stove platform over snow?

Several 2" dia.branches laid down first and then a ceramic blanket over them (http://www.inmainplumbingsupplies.com/en/new-products/Plumbers-Soldering-Flame-Blanket.html) Skidsteer has used that material also. He can fill you in on his usage.

Forced Air was originally used by the maker of the Sierra Zip to create a Forced Air Down Draft Stove. That stove did'nt go over very well in the third world countries where there was no electricity. The down draft story ended there.
.

davesailer
2009-01-07, 20:28
I have a set of instructions up at my blog for a "batch-loaded, inverted down-draft gassifier", based on what Rick Allnut and Ray Garlington did, but of my own design. You're welcome to copy anything there that looks useful.

The url is: http://ultralighter.blogspot.com/2008/06/gassify-me.html

Here's the top of the post:

"What this is about: A batch-loaded, inverted down-draft gassifier (wood gas stove)

"Name of stove: Inverted downdraft wood gas.

"Type of stove: A wood-burner that works with one charge of fuel at a time to produce a hot, smokeless fire.

"URL of original instructions: N/A. Rick "Risk" Allnut has done a lot of work (www.imrisk.com/woodgas/ddstove.htm), as has Ray Garlington (www.garlington.biz/Ray/WoodGasStove/). (For general info on light weight do-it-yourself stoves, see the Zenstoves links page at zenstoves.net/LinksGeneral-DIY.htm Also check out the Sierra stove at www.zzstove.com/).

"Description of difficulty: Requires drilling a lot of holes, cutting and positioning springy and prickly hardware cloth, reaching into a sharp-edged small can to place bolts. Not too hard. Not harder than the DOSIP semi-pressurized alcohol stove, but if you have large hands you'll need to start with a bigger can. Overall, this is no harder than anything else here, but is larger and involves working with steel rather than aluminum. You'll need some "real" tools."

Plug: I wrote two books on stoves (actually a whole lot more than just how to make them).

One is "Fire in Your Hand": http://tinyurl.com/5mm5j6

The other is a breakout on just the stove making part, with bigger illustrations (also available as a PDF) "Make your Fire": http://tinyurl.com/6ztsq4

But as I said, the blog post is the full section on the woodgas stove and you're welcome to it.

-- Dave

Jack
2009-01-08, 00:08
Good stuff, Dave.

I build a similar beast with empty Hummus cans, and use it to cook
lunch at work.

Wood pellets also work great in these stoves - Cub Scout proof, too,
as much as anything can be!

:bandit: