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#133883 - 05/18/10 05:06 AM Update on my downdraft gasifier wood stove
Pat-trick Offline
member

Registered: 06/22/09
Posts: 175
Loc: Portland, OR
The inverted downdraft gasifier, invented by Reed and Larson of Golden, Colorado, and made backpack-friendly by Ray Garlington. He offers a nice discussion of the design features here: http://www.garlington.biz/Ray/WoodGasStove/

I've been experimenting with this stove because i want to get away from fossil fuels entirely. I'm using a bigger, 4" diameter can that fits inside my 800ml Optimus Terra pot.

I'm getting close to a final "product", but am not there yet. However, I made a discovery. It is possible to increase the window for gasification of the wood, in other words the time that it happens can be lengthened indefinitely.

Read Garlington's discussion, it's concise. I will assume you've read it, so you will understand what I am about to say.

After about one minute, with the batch-loaded stove being lit afire from the top, gasification is operating. Blue and yellow flames appear to be coming out of the secondary air holes and there is no smoke. This little stove burns wood FAST, and we are using twigs, basically, so gasification is completed anywhere from 4-10 minutes after starting the batch. What I discovered is, gasification can be continued by chucking a piece of twig into the can every few seconds, before the flames stop. Instead of the "fire" going out, the flames will continue in gasifier mode as long as wood is added. Finding a rythym is easy, by watching the results 60 seconds later. It takes about 60 seconds for twigs put in the stove to affect the flames. They don't burn, they emit gas which rises, mixes with hot secondary air, and erupts into flames.

The stove's batch of fuel is added per Garlington's instructions, and it stops below the level of the secondary air inlets. (When this hot secondary air hits the wood gas, it instantly burns, thus the appearance of flames coming out of the secondary air slots/holes.) Tossing twigs through the feed slot of the stove keeps new wood in the gasification stage. As soon as the wood hits the hot center, gas starts coming off it. I was watching my twigs closely, and as they landed in the gassy zone, they looked like wooly caterpillars: little fuzzy-haired jets of gas immediately started coming out of the twigs. It's cool looking. It's not often I see a physical phenomenon displayed so graphically. Toss in the twig, gases come out, but not flames. The flames are above the pile of wood. The wood may be at the lower half of the stove's loading area, because it settles as it burns away, and the flames are at the top, above the secondary inlets. So it's a smoke-free fire.

I need to run more experiments with batch size, and I may want to go to the 3" diameter can, just to see if it's better. Also, my windscreen is a little large. I may make a "clip-on" screen, which would be like an extension of my added-on secondary wall. Maybe 3 slots for 3 legs of the windscreen. I'll do some pictures here. Directing the flames to the pot with the windscreen helps heating efficiency dramatically, but it makes for smoky puffs.

I can only add 5 photos per post, so I'll do more posts until all photos are up.


Attachments
inthebag.jpg

Description: 6-part stove in the Terra Weekend pot/cup set (800ml pot).

bagoff.jpg

Description: Take the bag off.

cuplidoff.jpg

Description: Remove the cup lid, which I protected with a paper towel, from scratches. It didn't work. There are scratches on the SIDE of the cup (and pot). The windscreen will need to go inside the pot, after I alter it to fit.

windscreenout.jpg

Description: Here's the windscreen pulled out of the pot. I'll probably cut this in half, leave 3-4 "legs" that will fit into slots in the secondary aluminum wall.

stoveout.jpg

Description: Here's the stove pulled out. I doubled the # of bottom primary air slots and top secondary air slots yesterday, and it works more smoke-free.


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#133884 - 05/18/10 05:20 AM Re: Update on my downdraft gasifier wood stove [Re: Pat-trick]
Pat-trick Offline
member

Registered: 06/22/09
Posts: 175
Loc: Portland, OR
Where was I? Okay, here we continue the pix.



Attachments
papertowelinpot.jpg

Description: The pot has a paper towel, too. Okay, the bottom of the pot was protected, but not the sides. Ouch. This was a gift, and I hate that it's scratched. The windscreen needs to go inside the stove, and I need to figure how to protect the pot's coating from

stoveout.jpg

Description: Pull the stove out of the pot, it's an ugly tin can. Twice as many primary and secondary slots now.

uglytincan.jpg

Description: OK, so there's the stove, and the secondary aluminum wall is visible at the top. The wire mesh and wire pot stand are in there, too.

stovepartscomeout.jpg

Description: Here the stove parts come out, and are visible.

screen.jpg

Description: Here's the screen, to keep wood off the bottom of the can, so air can travel through the wood from the bottom toward the top. Or does the air travel DOWN through the wood. I really don't know.


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#133885 - 05/18/10 05:28 AM Re: Update on my downdraft gasifier wood stove [Re: Pat-trick]
Pat-trick Offline
member

Registered: 06/22/09
Posts: 175
Loc: Portland, OR
Part 3.



Attachments
secondarywall.jpg

Description: This is the secondary wall, made from aluminum flashing stock. The top is bent over, to seal the hot air from escaping anywhere but into the fire zone.

secondarywallon.jpg

Description: The secondary wall can be spread a little and placed on the outside of the stove. I'll use the wire to snug it in place.

uglypotstand.jpg

Description: Ugly pot stand. I'll make a different one, maybe with hanger wire. This one is a one-of-a-kind thing.

potonstand.jpg

Description: Pot stand is on the stove now.

windscreennext.jpg

Description: So here's the pot on the stove, and the now-defunct-'cause-it-scratches-my-pot!-windscreen.


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#133886 - 05/18/10 05:34 AM Re: Update on my downdraft gasifier wood stove [Re: Pat-trick]
Pat-trick Offline
member

Registered: 06/22/09
Posts: 175
Loc: Portland, OR
Last post.



Attachments
feedhole.jpg

Description: Feedhole. 1.25" tall, 1.5" wide.


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#133888 - 05/18/10 07:12 AM Underload, let burn 3 min w/out pot = smoke free! [Re: Pat-trick]
Pat-trick Offline
member

Registered: 06/22/09
Posts: 175
Loc: Portland, OR
I made an adjustment today (early worm gets the bird). I underloaded the batch of wood, putting the bigger sticks only halfway up toward the secondary air inlets, and smaller stuff on top. Total batch about an inch under the secondary inlets. Then, second adjustment, I let it burn for 3 minutes without putting the pot on top. This has been the smoky time of the stove, putting the pot on top before the fire is really going hot.

So I put the pot on at 3 minutes, and there was a violent boil of the .8L water at 9:45 (6:45 after putting it on stove).

I started augmenting (adding to) the wood in the stove at about the 5 minute mark, a couple pieces a minute maybe. It burned with great flame all the way, and no smoke! When the flames were their biggest, wrapping around the cookpot, there was some slight black/sooty smoke at the ends of the flames. But keeping the flames on the bottom of the cookpot resulted in no smoke at all.

Last night, after I was done experimenting, I fed the stove like it was a campfire. It took some pretty big chunks of wood, no problem. When it's hot, it will burn whatever it gets. And..... no smoke! As long as the wood is below the secondary inlets, there is no smoke. So it's a smokeless campfire!

huh, now all i need is a date that backpacks. or a buddy. we can stay up late and talk all kinds of nonsense around the smokefree campfire.


Edited by Pat-trick (05/18/10 07:14 AM)
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#133896 - 05/18/10 10:46 AM Re: Underload, let burn 3 min w/out pot = smoke free! [Re: Pat-trick]
hikerduane Offline
member

Registered: 02/23/03
Posts: 2123
Loc: Meadow Valley, CA
Keeping the fire going, kinda like years ago when I cooked over small fires, gotta keep feeding it. Interesting about the air mixing with gases and burning thoroughly, thus no smoke. I'll have to read up on this, never gave much thought to it all.

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#133915 - 05/18/10 07:43 PM Re: Underload, let burn 3 min w/out pot = smoke fr [Re: hikerduane]
OregonMouse Offline
member

Registered: 02/03/06
Posts: 6371
Loc: Gateway to Columbia Gorge
Just a reminder that in many areas or seasons in the western US, wood fires (whether in stove or open) are not allowed. This is either due to fire danger or (in areas near or above timberline) the desire to leave what few pieces of dead wood exist to rot to help sustain the thin soils at those altitudes. In other words, you might want to consider an alternative fuel source. Alcohol is not a fossil fuel, by the way.

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#133924 - 05/18/10 09:56 PM Re: Underload, let burn 3 min w/out pot = smoke fr [Re: OregonMouse]
hikerduane Offline
member

Registered: 02/23/03
Posts: 2123
Loc: Meadow Valley, CA
Good point, I forgot to mention campfire restrictions later in the Summer in some areas at least out West. Reminds me too, when fires were allowed in the Desolation Wilderness in C, years ago in my younger days it seems like now, I always had to scavenge hundreds of feet for campfire wood for a fire and to cook over also. One trip at a very popular area, I found all the twigs I needed for my cook fire, I still had to hunt for larger stuff for a campfire. I think folks looked over the twigs as they needed larger wood for a fire. Now I just have a campfire where wood is plentiful, I stay cleaner, smell a little better and have time to read when not bringing wood to camp.

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#133964 - 05/19/10 07:52 PM Re: Underload, let burn 3 min w/out pot = smoke fr [Re: OregonMouse]
Pat-trick Offline
member

Registered: 06/22/09
Posts: 175
Loc: Portland, OR
Originally Posted By OregonMouse
Just a reminder that in many areas or seasons in the western US, wood fires (whether in stove or open) are not allowed.


I'm in upstate NY, can't afford to travel. But access to wilderness areas is two miles from my front door.

I wonder if carrying and burning wood pellets or hardwood chips would be legal. That would be better than polluting the planet and killing a bunch of waterfowl with oil accidents. Although carbon is released by burning wood products. There's probably not enough outrage in the general populace for there to be a movement toward a more natural type of stove. Besides the canned fossil fuels are super quick, clean (if we ignore oil spills, etc). But why do we have to be quick out on the trail? The biggest pleasure for me on the trail is the lack of pressure/urgency to do anything.
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#133983 - 05/19/10 09:34 PM Re: Underload, let burn 3 min w/out pot = smoke fr [Re: Pat-trick]
hikerduane Offline
member

Registered: 02/23/03
Posts: 2123
Loc: Meadow Valley, CA
Out West at least, when fire restrictions go into effect, usually in August, no fire/stove is allowed that cannot be shut off. This would include wood product stoves, alky stoves, Esbit type I imagine too. Campfires would only be allowed in established campsites, such as a campground, like car campers would use and permissible stoves would have to be used in established campsites in the backcountry is my understanding.

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#133993 - 05/20/10 12:11 AM Re: Underload, let burn 3 min w/out pot = smoke fr [Re: hikerduane]
OregonMouse Offline
member

Registered: 02/03/06
Posts: 6371
Loc: Gateway to Columbia Gorge
In the Pacific Northwest, we often get fire bans in August and September that forbid even fires in fireplaces in designated campgrounds! Funny, the bans are lifted as soon as hunting season starts in October, even if it hasn't rained yet!
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May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey

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#134045 - 05/21/10 03:01 PM Re: Underload, let burn 3 min w/out pot = smoke fr [Re: OregonMouse]
Bushman Offline
member

Registered: 07/01/09
Posts: 122
Loc: California
I must agree, portable wood burning stoves are more a hassle than its worth, not only with the fire restrictions that are often enforced but I find them too finicky. If fire restrictions aren't enforced I would much rather just have a small personal fire. Thats just me.

Though I tired making a windscreen/pot stand out of a soup can for my alc stove that can also be a wood stove, but ended scrapping it.

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