The Barrel in Barrel in Barrel gasifer

The idea comes from @KristijanL with his last build, utilizing the internal heat to preheat the incoming air and then I want to heat the hopper like some of the old Imbert gasifers did. Using a hot hopper to dry and cook / pyrolysisation of the wood is always a plus. The outside barrel is a heat shielding, with cold ambient air coming in from the side and bottom. Any condensation it drains out the bottom.
It also has to be able to service it with a yearly tear down for clean out of the hot moderator hopper this area will also serve as a ash / soot drop out for the gases.

In the hopper I added a tar drip that @trikebuilder57 Al Flick had this on his gasifer. He said he used less wood because of it.
With the tar vaccum vapor / moisture removal system that Joni came up with added to the hopper, I think this will be a winning combination.
This will be a slide into the back of my truck unit or a smaller size gasifer on the back bumper hitch like Joni has designed.
It should be able to run a small V-8 to 4 cylinder engine, by changing out the size of the unit or restiction hole size.
I am trying to keep it as simple as possible a Barrel in a Barrel in a Barrel.


Ha ha ha! I’ve been sitting in the house all winter because my LP Torpedo heater makes so much water that it was socking my tools. Finally came up with a plan. An outside wood burning hot air furnace to heat the shop. Measured up my barrels and found I could do a barrel, within a barrel, within a barrel, to do it. So went out in the sub-freezing weather to gather the barrels and to my surprise, I couldn’t lift one in particular. I bumped and banged and pushed and shoved but it wouldn’t move. Wow! That was really frozen to the ground. Started working under it with a spud bar-- opps ! it moved. Good! Not frozen to the ground, so went to push it over to roll to the shop. Dam. I couldn’t tip it over. Finally got it on it’s side only to find it was 1/3 full of ice. The bungs were in but not tight and I think heating from sun then cooling, pumped the water off the lid into the barrel. TomC Hoping you got your barrels inside.


Ha Tom, water is sure heavy frozen or not, easier to get out of a Barrel if it is in liquid form.
I am still looking for the barrels. I have seen some free ones hope they are not iced up inside.


Making it simple.

After looking at the drawing I realized that I could put the outside barrel (blue) over the top of the whole gasifer and slide it down. I just have to unscrew the tar vaccum vapor pipe, and the gas out pipe. Put the blue outside barrel into position and screw the pipes back in. I might put a little insulation in the very top.
I think if I have a 1" to 3/4" clearance between the two barrels (blue and green) that will be enough.
And 1" to 2" on the hopper / firetube barrel and the middle barrel (orange and green) that would work okay. Give some extra room for ash/char to drop out and soot build up.
On the very bottom under the gasifer put some insulation.
I am trytrying to use up all the extra heat that comes off a gasifer unit and put it to use.
I like the idea of using the height of the gasifer for ash/char/ soot drop out area.
In the back of a truck bed the gasifer could go on the passenger side and have the filter over on the driver side. Wow I can look out my center rear view mirror and see behind me. I like that.


Good morning Mr. Bob.

Thanks for putting up the design. Looks really good but the only way to see how well it will preform is just built it and operate it. I think in most cases it is just too hard to foresee what may occur with a new build. I think it may take a few generations to work out all the kinks .

Engineering can take you just so far and then it will depend on trial and error.


Mr. Wayne; This is an excellent post. Mr. Bob is a doer but I sure get tired of those who “read” about woodgas and think that qualifies them make long dissertations on each posting. You have to experience that 75%. TomC


Yes you are right Wayne, a drawing on paper is just that a drawing, I am just trying to figure out how it will all go together. This will not say it will work, but actually building it to the right proven dimensions it should work.
This site is great for getting ideas out to the members and then getting back input from members. The only thing stopping me from going out a start building is the 30 * f cold weather with a mixture of snow / rain. Looking forward to Sunshine and warmer dryer days ahead.
I have a question Wayne, as you know I still have the old firetube core you built 2012. I am planning on repairing it and making a new improve firetube from it. Of course this will be done on the WK building side of the DOW site. But the rest of the build of the gasifer that the firetube will be sitting in is different from your WK gasifer build. I was wondering if I could show the non WK part of my build on the open side of the DOW site. Leaving out the WK part of the build.
In the pass we have had members sale their unfinished WK firetube projects to people on this site. Once a firetube is built, just looking at it from the outside does not reveal how it works inside. That is the big secret.
It is just a thought. You and Chris can make the decision on this and I will follow according to your decisions.
You might ask why I want to do this. I just want to show the people it is the WK Firetube that makes the big difference in turn down idling ratio and performance vs. other firetube designs.

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Hello Mr Bob .

What you have stated above is fine with me .

Sure wish I could help more by studying the drawing but I know very little until the fire is burning and the miles are accumulating .


I am concerned that the venting at the top of the hopper should be large enough and have a throttling valve.
Too much venting could suck the fire up from the nozzles, not enough would allow too much water into the burn.

My first hopper did not have the external cooling tubes and resulted in excess soot and tar. After rebuilding with 12 1 1/2” cooling tubes, I have never had a problem with moisture cooling the burn.
Try to route the suction tube as vertical as possible to the Venturi as the tar will try to freeze as soon as the gas cools.


Yes I do agree about the vaccum tube would need to be insulated if it is to far from the exhaust pipe Venture. It needs to be designed so it can over come the 5 to 10 inches of vacuum in the hopper when driving down the road and also work at idle.
If the fire lobe goes up a little at would be alright. This would encourage pyrolysis of the wood and moisture/tar vapor would then be removed through the vaccum tube at the top of the hopper. The only way to find out is try it.

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I never thought about the amount of vacuum needed. If not enough all you would accomplish is to pull engine exhaust into the hopper, NOT what you want.


Yes, before I do anything I think I will try I on my 92 Dakota truck. Build a extension on my exhaust pipe with a the ventrui on it and hook up a vacuum gage and see what kind of vacuum I can create with it. If I can create 20 in. of vacuum great that will work.

Hello Bobmac,
I think it’s time to tell me a few words about your project … So, I’m not going to criticize or teach you, I’m just trying to express my opinion, based on my own experience …
The first thing I didn’t like was the complete heating of the bunker with waste gases; I have long noticed the specifics of the operation of this type of gas generators (with heating) on ​​wet fuel, and it does not make me happy … From the moment of start-up and until all the fuel that is left, the car runs very badly, but when the wood is dry it becomes very good. The second drawback is the high cost of materials that will be spent on the heating jacket and the body of the heat shield, in my opinion it will not do anything good.
My third discontent is associated with the air collector around the gasification chamber, while making it you need to remember the simple rule that all processes try to go through the path of the least resistance … So your project has a lot that is superfluous and unnecessary. Let me remind you that this is my personal opinion.
Best regards, Evgen.


Het BobMac,
Read this. Really really read this 1945 Finnish publication JanA put up. And study this.

My hope is this will cause you to re-think this barrel-in-barrel idea.
I set up the three barrels back in ~2008 before I met Ben Peterson. The three barrel idea would have even worked. Kindda’ sorta. Been heavy. Demanded super pre-dried wood. Been a rusting pin-holeing PITA by the 3rd, 4th season. Too damn expensive to do in SS nesting barrels. $750 + $500 + $350 for the new SS barrels.

So a bit puzzling why you want to go backwards from your trucks WK?
And make a system far too big and heavy for your Suburu projects car?
I thought that was to be a charcoal system?

Bob most of the time old heavy iron as in this original WK hearth tube needs to be retired out as a yard ornament.

In truth cut up boned out to unrecognizable scrap like BenP and Jodi recently did is the only safe way.
BenP sold, moving on with his life from wood gasification; one of his early historic saved back first years systems. His carbon steel ~2007 year Woody unit.
NOW the owner put it up on youtube as inadequate needing modification improvement to function. He really, really regrets ever letting that early ideas system out of his control. He shoulda’ just scapped it. Now moved on he DID scrap out all others.

Clessie Cummins the Cummins engines originator to win at the Indianapolis 500 used a diesel 2-stroke and a 4-stroke entry. The 2-stroke was made up to give the gotta’-try guys in his organization a bone. It was the 2-stroke that won in it’s class.
But he knew that true useable working diesel would long term be 4-stroke. Fuel economy. Less maintenances. He had that 2-stroke dumped into a deep dark river to disappear from his company’s history. A latter competitive Indy500 4-stroke was what was displayed for years in the companies lobby.
Ha! Ha! Mr Wayne proves to be a real Use-It-Up, Wear-It-Out kinnda’ guy. Not a spit and polish History preservationist.


This is good conformation as I was looking at my drawing this morning and noticed what you are saying. I was reading this morning some pagers 1945 from the University of Helsinki’s Laboratory technical Journal on tests they had done and came to the conclusion the hot hopper used with a Imbert gasifer was not going to work as good as a cold hopper on a Imbert. They said the larger hopper with moisture collection tubes on the outside worked the best with condensation collection for tars and liquid. This sounds like Wayne read this article. They also tested the vaccum hopper vapor tuyere using the exhaust system, they found some gases were removed from the hopper and lost out the exhaust pipe. But the weight difference of the gasifer was less than having the hopper condensation tubes on the side of the hopper. This is where you are keeping your unit light weight.
So it looks like I will be making a revision on my drawing, The 3 Barrel idea is going to change a little. Also the hopper will be slightly larger and will be open to ambient air flowing around it. They also found that preheating the incoming air was more effective. Yes less drag on the gasifer system is very important. I have to keep this unit simple. Thank you for your in put. I appreciate it.

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Thanks Steve I have already read the report.

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Bob it was with great reluctance I said as I did.
Obviously you have the need to build something. Cheating death does that to a fellow.

Anyhow . . . since you did read that article when I saw that actual Finnish racers photo of his boxy shaped monotrator. And reread his needs-reasoning for it - low visibility, with still a reasonable fuel storage on-board . . . I could not help by think back on your topic “refueling on the fly”.
Then I saw a “Tee” across the top barrel.
The engineers analysis said the held side inert fuel was an additional cold areas encouraging condensation.
And a vehicle has the side to side shaking to center settle that fuel reserve into the center active.

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Guys, I’m all for condensing hoppers and I don’t doubt the Finnish report
We need to remember this was all done in a short period of time in 1945 and the monorator inventor didn’t even know what he was up to.
They produced excellent documentation, but I doubt they produced as many wood burning hours as we have on this site. Nothing can compete with induvidual long term first hand experience.
We all know by now how small differences in input can completly change the outcome. What appears to be identical systems can behave differently and even one single system can behave differently over time.

Well, what I’m trying to say is…
My personal experience is that with a wide hopper the “side to side shaking to center settle that fuel reserve” doesn’t happen easily. Especially if the chunks are condensing wet, cold and gluing to the sides.
And this dripping wet outer layer of fuel - where does the dripping juice end up? On the funnel to collect tar and be steamed off again? Maybe they used a mesh funnel - but then that would make a bottom mess of mixed tar and debrie over time and the drain would get plugged soon enough.
I believe what this 1.0 monorator lacks is separating the falling and condensing fumes from the hot rising ones. WK-tubes would be the no1 solution, inner wall no2 - in my personal humble opinion.


Did anyone look at this video ? It shows a large fleet of city buses powered by wood gas . I think they knew what they were doing .

Sure HenryB.
Many of us have examined this video in detail.
As J.O. said . . . .state of the art for 1940-45.
At 0.42 it shows the bus pulling up to re-fueling station #2. On the roof your see a square box manifold at the base of an exhaust cone. Then you see above station #3 two conical exhaust cones. So they WERE externally heat and forced air drying down the wood fuel for best results in their non-condensing systems.
1.02-1.09 they show using a direct contact of wood char to metal system. Sweden was a long term metals making country and at this time they could make up to 40% nickel refectory metals. And Stockholm as their premier city would have the best possible.
1.59 is the first showing a man raking out lower system accumulated slipped char/soots/ash. Shows up again twice later.
Ha! Ha! 2.14 shows a second man standing far back throwing lit matches into the just opened up hopper covers to flare burn off gases.
3.13 then shows man #1 rodding down TWO separate gasifier reactor under an earlier? later? trailer system prior to sack fuel dump reloading.
A fellow can continues detail watch and see bits and pieces of state of the art 1940-45.
6.45 shows fuel trailers now having SIX high pressure fuel gas cylinders. I am betting acetylene. Not compressed woodgas. Plug in and run without all of the woodgas trailer maintenances.
Then no need for the driver or a second man “fireman” to go back as needed to grate shake and/or rod a system down.

So . . . I think with the evolved WK system we are doing much better directly use today.
Steve unruh

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