Wood gas is a syngas also known as producer gas which is produced by thermal gasification of biomass or other carbon containing materials such as coal in a gasifier or wood gas generator or producer gas. It is the result of two high-temperature reactions (above 700 °C (1,292 °F)): an exothermic reaction where carbon burns to CO2 but is then reduced partially back to CO (endothermic); and an endothermic reaction where carbon reacts with steam, producing carbon monoxide (CO), molecular hydrogen (H2), and carbon dioxide (CO2).
In several gasifiers, the actual gasification process is preceded by pyrolysis, where the biomass or coal turns into char, releasing methane (CH4) and tar rich in polycyclic aromatic hydrocarbons (PAH). Other gasifiers are fed with previously pyrolysed char. Wood gas is flammable because of the carbon monoxide, hydrogen, and methane content.
It's an open source type. I'm short on time right, but I'll post some more info/links latter. For example the FEMA one on how to design one.
Millions of them were used during WW2. They are ok for steady rpm engine running. One needs to have a big engine to make the same hp.
One of my uncles was around them during WW2. He told me that they are really only for emergencies. He was stationed in N. Italy during the last part of the war. He said he got to ride down the mountain, walk on the flat & push going up the mountain.
Yep, real popular in Europe after the Nazis used up all the gas available. My Dad told me about them, many civilians used wood gas conversions on their cars and trucks as that was the only fuel available. Dirty though, without an effective filter system the engine gunks up pretty quick. You had to really finnesse the throttle, as was stated above best for constant RPM engines. IIRC, there was a factory made woodgas version of what became the Volkswagon Beetle produced by the Germans, had like a big rubber pressure bladder on the roof to store the gas so it had better throttle response.