A few charcoal gasifier questions

just a few charcoal gasifier questions.


do updraft charcoal gasifiers require a puffback lid? or are puffback reliefs more for downdraft units?

i know in my simple fire charcoal unit i simply put the gland end off a hydraulic cylinder on top with an oring, but i never bolted it down, with the idea that if it did puffback it would simply blow the gland off the top. However, i did notice a few times when trying to pull the engine over it would puff back and all the gases would just shoot out the air intake. Does this mean there isnt quite as much need for some sort of puffback device as there would be for say a downdraft wood gasifier?

Also i was doing some reading on air velocities in wood gasifiers, talking about how high velocities produce hot gas but crack all the wood tars and produce less charcoal, subsequently low velocity systems produce more charcoal with cooler gas but higher probability of tar production.

That leads me to question #2, does nozzle air velocity matter as much in a charcoal gasifier? since we are already burning the charcoal that means that charcoal production is something we don’t have to worry about. We also don’t have to worry about tars since we have already eliminated them. that just leaves gas temperature, i would imagine we would like as low a gas temp as possible, so when gasifying charcoal would we want a low velocity system? or does a low velocity system also affect our co2 to co reduction?

sorry if these are beginner questions!


I feel like a puffback lid would be a good idea, I’ve had one event in my Mazda and it blew my water drip hose out of the nozzle.

Also you do want a decent air velocity speed to keep the bright orange to yellow glow, you want to convert as much CO2 to CO and water to Hydrogen as you can.

For my Mazda I used 5 .5" holes in my flute nozzle. I feel like I made the best gas after 2000 RPM.


Did you not have any puffback system on the mazda at the time cody? is that why the water drip hose blew off?

So a lower velocity system, producing less heat will not convert as much co2 to co, is that correct? i definitely understand with a water drip how you would want to keep the flaming zone as hot as possible because the splitting of h2o is an extremely endothermic process.

without a water drip system though, will our co2 to co reduction also suffer? if we had a low velocity system, keeping the flaming zone more of a cherry red (900-1000C or so) would we notice less co2 to co reduction as opposed to a bright orange/yellow (1000-1200C) ?

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Regardless of what type of wood gasifier it is or what direction it drafts, you should always have a means to relieve presure in the event of a flash back.


definitely was the lines i was thinking. part of my asking is that a lot of folks seems to make their gasifiers out of steel drums with removeable lids, and simply use high temp rtv or stove rope to seal it, and then proceed to use that lid as their safety relief. my problem is i cannot find any of these barrels in my area, and ive looked for a long time, and i dont fancy the idea of spending big money on a brand new one. so i’m left with having to cut and weld old tanks instead, and the safety lid is going to be a challenge for me, especial a system that seals well. my fabricating skills are quite horrible and i think building something that seals air tight is going to be a challenge for me to say the least.

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I think a popoff valve would be sufficient, or making a lid like Gary Gilmore and Steve Bowman have done, it can be applied to a non barrel lid.


I didn’t have a spring loaded lid, no, I used a locking ring so it couldn’t move. It happened when I mashed the throttle too quickly. I really got off easy with that event, it could have blown the lid off if it was a stronger puff.


Justin , if you are building a stationary unit to run a generator then don’t bother with a puff back lid , in all the years of running i might have had maybe 1 blow back and that was really just a wet fart , any build up of pressure will find its way into a couple of places … 1 will be your air inlet /nozzle and the other will be the air/gas mixer valve , sure you can argue its a good idea to have one but really its not needed , loose fitting plastic hoses onto the barb of your carb will work just as well as a safety valve .


My experience is the same as Dave’s.


Justin, I feel your pain. I don’t like the looks of the things I make either. I have to tell myself ‘Don’t try and make it look like it came from the store. Good enough is good enough’.
So anyway I’ve come up with a simple type of cover that I’m happy with. Basically its just a thin, flat piece of sheet metal sitting on top of a ring. The piece sheet metal has spring force applied at it’s center.
The surface of the ring is ground to a flat plane by using a piece of coarse sand paper, 60 grit, glued to a sheet of glass. I weld a flat head carriage bolt to the center of the sheet metal. To prevent the sheet metal from warping I clamp a large block of aluminum behind the weld to act as a heat sink.
The final step to create an air tight seal is you put a sheet of plastic wrap over the ring and just a smear of RTV on the cover. Close the cover so that the rtv gets squeezed just a little and let it cure. Next day open the cover and peal off the plastic wrap. It should seal really well. Note: The acids in woodgas will take off any paint that’s on the underside of of the cover, you may want to take it off before you apply the RTV.
I haven’t gone into every last little detail. Ask me any questions.

Here is a link to one I made.