Downdraft Charcoal Gassifier for small engine generator

I shouldn’t be doing this right now but I came across this bladder tank while cleaning 30 years of accumulation out of my shop/warehouse and the wheels between my ears started turning.

So when I got back in the house I did a drawing of what was between my ears.


Wow Don. That tank looks perfect for a charcoal gasifer. Sometimes you just live right.

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Hey Don, Why the “fluted” nozzles? Wouldn’t conventional nozzles give more of a complete Hell Hole? TomC

Hi Tom,
We had a discussion about double flute nozzles over here a while back. The double flute charcoal gasifer - #8 by KristijanL I never tried those so thats what I would like to experiment with.
You staying warm there across the lake?


Hi Don; Had a full day of snow and now the temperature has dropped to “0” and the wind is drifting everything in. I think this one is going NE and won’t make it over to you. TomC

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Hi Don, I am doing a ring nozzles, on my unit. It should be about the same.


I really like that Don.
What size engine will this run?
How will you calculate the size and number of holes for the flutes?

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I’m anxious to see how it works and lasts.
That thing is very simple.
Keep us updated.

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Bill, I have a 9hp engine on my charcoal lawn tractor with a 1/2 inch ceramic nozzle that works pretty good; enough to pop wheelies. :grinning:
I have a 5500 watt genny with a 12 hp engine I would like to use this downdraft on so I am thinking 2 flute holes 3 inches apart on each side facing each other staggered so that the holes don’t blow on each other and that will create a large reaction area. Nozzle holes 3/8" or 7/16" should be about right the way I have it figured.


Has anyone thought of a dropbox/cooler combination for a small gasifier?

Do you think this will work?


I tried something like this but had to much heat to make any difference. Even though I was constantly pouring water over the 33 gallon barrel .

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Hi Don, how about adding a preheater for air going into the box and out. That will help remove the heat in the hot dirty gas coming in. The soot will also collect on the fins of the preheat.
Are the fins on the inside of the box? The fins should stiffen up the walls and keep it from flexing with a vaccum draw.
It should work great with the low pressure drop out areas going in and also out.
It looks like it would be a space saver too, not being a barrel shape, fitting in the corner of a truck bed.

3L 4 cyl run on 3 cyl 2.25 L 1800 rpm , Heat .

What do you think would be the smallest ID pipe that you could run chargas through without constant cleaning. I’m talking about multiple pieces of pipe. Been thinking about water cooled piping. Your box drawing gave me an idea. If the area to the left of your diagonal bulkhead were sealed and the gas was move though maybe six sealed tubes surrounded by water and the water recirculated through a small radiator you could drop the temp of that gas below ambient in a fairly small area. I’ll be working on something like that if winter ever ends.

Hey DonM.
How about on your cooler box side putting in some open ended air tubes hole cut and welded into the top and bottom walls.
Then, natural rising air flow would cool.
Sure fin the outsides too.
Steve unruh

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I was thinking the fins would be on the outside only as this would not be the only cooler in the system. The drop box was mainly to eliminate the cyclone restriction.


Is there great resistance in a Cyclone?

Yes Jan, that is why we use a drop box to separate some of the heavier char/ash, using a low pressure drop. Also it is a great spot for a air heat exchanger, being 800* f at the cross over entrance to 450 * f at the exit into the cooling rails. It does take up more space then a cyclone, but no extra vaccum drag on the gases. The cooling rails and condensation tank pick up the extra soot before the final hay filter gas cleaning.

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Thanks Bobmac.
How big does it need to be?

That is a good question. Lets say you have a 3" or 8 cm diameter across open coming out of your gasifer I would multiply it by 4 or more. 8 × 4 = 32 cm diameter across. If you put a heat exchanger inside make it larger. Have a drop out area like 6" or 15 cm below where the dirty gas comes in to catch the char/ashes. You can make it as high as your gasifer. Look at some of the other gasifer builds that have a drop box. You will want to have a clean out open in the bottom.