What is wood gas?

When wood is heated with too little oxygen to burn completely, it breaks down into a mixture of carbon monoxide, hydrogen and methane. That mixture — producer gas or wood gas — is combustible and can run an engine.

It is genuinely proven technology. It also carries the most serious hazard covered on this site: carbon monoxide, which is invisible, odourless and lethal well below concentrations you would notice.

The engineering difficulty is not making gas — it is cleaning it. Tar and particulates destroy engines quickly, so cooling and filtration determine whether a system runs for years or for hours.