I got a little dairy on a 10 or 20 minute quicky I built to make charcoal and gas from wood. Lots of ways to do it and most work, some better than others depending on the use intended. I need alot of charcoal and baking the gas out of the wood to make the charcoal makes the gas. I can clean and cool that gas and then run a gennie on it or about anything that would use propane.

As for building a normal gasifier that burns the wood, starves out the oxygen, then the heat bakes more gas out of the wood which cannot burn do to lack of the oxygen, those work too and are not that hard to build either. You do need to be sure it is well sealed at joints and such. Most of those types work by vacuum. The engine sucks the vacuum on the system which is what draws in the air and burns the wood etc.. If you have a leaky joint or weld you loose vacuum and suck air and it does not work well.
You can built it as an up draft or downdraft type system. Each as it's own advantage I geuss. One sucks air from top and burns at bottom, the other is reverse and sucks air from bottom and burns at top. Big advantage for the down draft is the top does not really need sealed and you can add wood while using it. An up draft will loose the vacuum and stop working if you open it to add more wood, though you might be able to build it different ways and avoid that.

 I started on those to but stopped for now. For stationary use like a gennie or stove I feel I am better making charcoal and getting gas that way. For motor feul for a vehicle I am now trying making alcohol instead. My main problem with a gasifier for a vehicle is each vechicle would need to have one. I have 4 being driven now, and alot more sitting here used seldom. If I could compress the gas from the charcoal maker into a tank and carry it like propane that would work for me. Untill I can do that though, I think alcohol will fill my currant needs better.
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nothing to lose