A few years back, I read up on wood gas, and learned just enough to feel it was more trouble than it was worth for powering a car/truck. It has 1/4th the power of the original engine, (must use a V8 to get 2-cylinder performance. The reactor is bulky and cumbersome. Engines accelerate and slow down, the reactor produces gas at a fairly steady rate, etc...)
I am now a fan for using woodgas to power a piston electrical generator.
All the most popular designs used what I now know is a downdraft, gravity feed reactor that uses wood pellets of a specific size. I can make a machine to produce wood pellets from sawdust, but there were three different things that turned me off of woodgas.
In the advanced efficient wood gas reactors, the wood pellets flow down a steel tube onto a grate. There is a flame maintained at the grate, and due to air being pulled down, the flame is pulled down. Just above that flame is a thin layer of hot pellets that are not experiencing combustion yet, and they produce woodgas...if everything is "just right" After off gassing for a little bit, the ashes below get shook through the grate into a catchment area.
Then the off gassed pellets reach down to the combustion layer next to the grate, they get turned to ash in the process of making the heat.
I never knew why the combustion and the Pyrolysis (off gassing due to heat) had to be done in the same place. If you burn wood with air/oxygen...you get heat and ash. Any gasses that are accidentally produced make funny shapes and colors in the campfire, and are obviously burned up in the flame.
Charcoal is different...the primitive way to make charcoal is to make a small bonfire, and once all of the wood is fully engaged, you bury the pile to choke off oxygen, while holding in the heat. Why did ancients make charcoal? It burns with less smoke than wood, plus for smelting or forging, it burns hotter than wood.
A couple days later, they dig through the pile to separate the ash from the charcoal bits. For simple woodgas production, we need to separate the heat (wood fire, or concentrated solar), from a metal box of wood bits that cannot get any oxygen, and the interior temperature is controlled at a best level.
A dirty syn-gas comes out, and we have to separate the char dust, tar, syn-kerosene, and also the gasses. The gas is mostly H2, which is what we want to run a generator, but there is also carbon monoxide (CO, which I was surprised to read is flammable), and also some methane. You can burn them all together, or separate them further. The purer the H2, the more invisible the flame becomes. If the flame is blue, it also has methane, and orange means you are making some CO.