Cody's Hopefully Raw Wood Reactor

Making a new topic so I can keep my thoughts in a semi orderly manner. After looking at JO’s build in his Mazda and his old Rabbit reactor as well as Jan’s reactor for his S-10 I’ve been shown it’s not impossible to keep a small form factor. I have a roughly 10" OD air compressor tank, a few 20lb propane tanks which are 12" ID, the car rim that I have already cut to fit propane tanks, my 20 gallon drum, and the two pairs of brake drums that I’ve been able to take home.

While the idea of a grateless system sounds exciting it’s entirely foreign to me as a concept. I know JO and Jan really like those systems and seems to work well for them.

The only things that I am absolutely certain of is to make a heat exchanging air jacket using the air compressor tank as the burn tube, and the propane tanks nested over. I have metal band strap material and I have worn out steel cutting bandsaw blades. The other item I’m positive of is utilizing a brake drum system on the bottom end.
If I were to build this grateless I would use a propane tank as the base and cut the disc portion from one of the brake drums.
I could also go to the scrapyard and try to find another intact 20 gallon drum and go with a self repairing angle iron swinging grate. From what I understand, Max Gasman shows a bird cage shape as the whole grate.

The car rim mates up perfectly with a 20 gallon drum and has a nice rounded shoulder, if I cut the burn tube to fit precisely in the propane tank then it would leave a mound to sit proud inside the car rim, which would give me a good condensate gutter. I really like Joni’s condensate exhaust venturi so I would be tempted to use that.

The vehicle this would be intended for is my Mazda.

The smaller brake drums already have a 3 inch center hole which sounds about right for the little 2 liter engine. JO used a 3.5" choke hole with his 2600cc engine so I’m in the ballpark.

I would be missing a step in some pre heating if I go grateless, heating incoming air from exiting gas, but I can make up for that with a drop box exchanger.

A lot of guys seem to have had luck with 7 nozzles and sources like Peterson’s book show 7 nozzles sounds about right. I will be welding in couplers to the burn tube so I can change out nozzles for repairs.

My main criteria is to not use up another 55 gallon drum because I am saving my last two for a WK. Same goes for my hot water heater tank.

I know I’ll have to use a small fuel size because the burn tube is relatively narrow being just under 10" on the outside.

Nothing has been welded together and only two cuts have been made that make sense.

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I’ll try to draw up the general idea.
Not entirely sure how far my jets should be from the restriction if I want to have them pointing down from a far distance, square direction from a suggested distance or upward like Joni does.

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Cody, I see my name mentioned.

Grateless means less fabrication and less maintence, but in certain circumstances it comes to the cost of drag and power. The middle way with a swinging bypass grate was always recommended. I just wanted to push limits and see for myself. As far as I know even Jan returned to using a grate.

What I’ve found is the exact number and sizing of nozzles aren’t that critical in a vehicle application. Neither is distance to the restriction. Just stay well above the 60° ash slope. Also, Joni mentioned a higher number of nozzles makes for richer gas.

The most important part is to keep the glowing char pile well insulated with ash cones or air jackets to protect it from transfering heat to the outgoing gas or to outer space. And of course - the bigger the char pile - the better it will self insulate.

The rest is up to the operator. A lot can be compensated for with fuel sizing.

Just a few random thoughts / JO


If you are going to make an Imbert, I think you should look in the library for the dimensions that are exposed there for your engine, I think they fit quite well, do not do as I do and make a too small fire pipe, it will be easy to hang the wood, and much worse gas. A real cyclone is not wrong either, I have very little soot in my coolers.


Yeah I’m judging my dimensions off of Ben Peterson’s guide and the Imbert chart, mostly the Imbert chart.


What was the inside diameter of your burn tube?

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The first one I made was 9 “, it did not work so well, hung up the wood and did not make much gas. The one I have now is 12”, and works much better.


I’m going with a 12" tube with my WK build, but hopefully this almost 10" tube I have planned will be good enough, I haven’t cut it open yet but it measures just a hair over 10" on the outside diameter. I already have small fuel size in mind for the most part. I’m setting up my electric plug chainsaw for a chopping station like Gary Gilmore does, until I can make a chunker or find one.

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I’m treating this wood unit as my learning experience before I build the WK. Getting air-tight welds, troubleshooting, etc.


Ok, I did not have a tube that fit, so I made a 12 "tube of a 2mm (0.08in) thick sheet and a cone of the same thickness.
They had Imbert up to 200hp, and 6-7 liters.


I’ll keep that in mind Jan. I need to buy a sheet metal roller in the near future so I can more easily make cones and cylinders. The machine shops around here all work for big companies so they don’t like small personal jobs.

I am thinking about for my connections between sections of the system to use 2" NPT floor flanges. Could silicone them up and bolt together for a more serviceable system. Use nuts with a taper on one end so they will self center.
I’m also trying to make the reactor itself not a chore to take apart for cleaning or repairs so I am on the hunt for another 20 gallon drum and lid for the bottom half.

These are what I use now for coupling together for connections that are high temperature beyond the high temp hose you can get.

For temps under 300* F just use the high hose and simple hose clamps. This hose can handle up to 500* but then your are pushing its limits.


One thing I do with those band clamps is I wrap the pipe connection with the silica cloth to ensure full seal.


After looking at the imbert chart and measuring the Nm^3/hr at just 3000 RPM(about 64 Nm^3/hr) I think I’ll be using the bigger pair of brake drums that have a 5 inch central opening. They also are deeper and thicker. I can always choke down if need be but it’s annoying to have to widen a hole.

I don’t have a tachometer in my Mazda but I just used 3000 rpm as a baseline because redline is 6000. Peak torque is generated at 2800 RPM for this 2 liter engine and peak Horsepower is at an insane 4800 RPM.

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Another bonus of using the larger brake drums for the hearth is I can put the nozzles nearer to the bottom of the tube itself, pointing down into the drums, giving a longer surface area for heat exchanging and keeping the worst of the heat off of the air compressor tank. I can also either coat with refractory or wrap in ceramic wool around the two drums to give me a better heatsink while idling. I have some bearing races that I can put in to give a lip for ash to develop around the restriction.

I made the tube with the help of these, the cone is also no problem to make, 2mm is not so difficult to bend. Conan keeps the ash as insulation, so I think it is good. Tom C had brake discs, but I do not know if he got a good run on that unit. 5 Metre Tie Down Ratchet Strap Lashing Straps S Hooks For Gazebos Tents | eBay


Keep in mind gasifiers tend to perform better with nozzles pointing up slightly. The torch like flame inside helps collaps bridges.

My policy is always weld things shut and use thick materials. Then there isnt realy a need for service, and the risk of developing a leak. Silicone or any kind of sealant aided joints ALWAYS gave me headakes.

The cast drums will cause problems on you if you intend to weld then to anything. Wich you need to do if you plan to make a air mantel around. If you plan to make a separate isolated route for air then there isnt realy much more point in using the drums any more…

As JO hinted, the best, cheapest refractory material is the ashcone. Where ever you have heat to metal contact you not only degrade the metal but also loose precious heat.


The drums are just being used as the restriction and reduction, but I mean I could just make my restriction out of a 1/4" plate welded to the end of the compressor tank burn tube.

I could also build it like a WK Micro with an elongated burn tube and nozzles being towards the top. The compressor tank isn’t as thick as a WK tube would be so I’d probably protrude the nozzles just a little bit to take some heat off of it.

Forgot I had these golf cart wheels. Might be able to use this as my upper and lower hearth, make an elevated restriction to let it self insulate. Has a better bell shape than the brake drums.

I will in all likelihood cut out the center of this wheel at the perimeter of the lug holes, but leave a shelf for a thicker restriction plate.

If you split the rim and only use the right piece (upper picture), you have a cone that the ashes get space outside, and make a restriction and put on top of the cone.