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

if we had room for two slip rings we could use em, but failing that, converting the commutator into one slip ring and the shaft end into another works for me. :)

good luck and keep us posted

Ok, if using this gas for an engine. Remember that it comes out with various impurties also. Tars and resins that are not good for an engine and depending on your setup maybe  even some ash.

The above is why you really want to cool and filter the gas well before running it. Cooling it will condense the steam, tars, creasote etc.. that will eat your engine.
 In the old vehicles it was cheap and easy to just pull a head do a vavle job and stick it back on. Not so with todays cars though! So where in the WWII days we find pics of the gasers mounted on the rear of a vehicle feeding an engine directly (it looks like) they could clean the valves themselfs for a buck in a couple hours on a saturday when needed :)

To cool the gas is easy, lots of ways to do that. To filter the gas I think charcaol would be about the best filter to use. I never got that far yet, but I was going to make a batch of charcoal then put it in another barrel as a filter for the gas. This charcoal would suck up the inpurities letting just clean gas by. When the charcoal barrel filter needs new charcoal I figure the dirty stuff can be burned as a heat source to bake the next batch of charcoal and gas.

It must be rememberd if using for a vehicle that the system must be well sealed for the engine to draw a vacume to keep the process running. Also when dealing with the gas from a gasifier you have alot of carbonmonoxide so a leak of escaping gas could be deadly, even worse so than a normall leaky autoexhaust would be.

I been busy with other stuff and gone awhile etc.. but I think this is something I may get back into myself also for One truck for now. You also of course have to have a way for the engine to get the feul in correct feul air mixture that various constantly for a vehicle whereas a gennie could just be setup to run a constant speed and forgotton nearly
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nothing to lose

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