A wood gas generator is a gasification unit which converts timber or charcoal into wood gas, a syngas consisting of atmospheric nitrogen, carbon monoxide, hydrogen, traces of methane, and other gases, which - after cooling and filtering - can then be used to power an internal combustion engine or for other purposes. Historically wood gas generators were often mounted on vehicles, but present studies and developments concentrate mostly on stationary plants.
Gasification had been an important and common technology which was widely used to generate Town gas from coal mainly for lighting purposes during the 19th and early 20th century. When the first stationary internal combustion engines based on the Otto cycle became available in the 1870s, they began displacing steam engines as prime movers in many works requiring stationary motive power. Adoption accelerated after the Otto engine's patent expired in 1886. The potential and practical applicability of gasification to internal combustion engines were well-understood from the earliest days of their development.
In 1873, Thaddeus S. C. Lowe developed and patented the water gas process by which large amounts of hydrogen gas could be generated for residential and commercial use in heating and lighting. Unlike the common coal gas, or coke gas which was used in municipal service, this gas provided a more efficient heating fuel.
During the late 19th century internal combustion engines were sometimes fueled by town gas, and during the early 20th century many stationary engines switched to using producer gas created from coke which was substantially cheaper than town gas which was based on the distillation (pyrolysis) of more expensive coal.
In about 1920 French inventor Georges Imbert created the 'Imbert' downdraft generator.
Imbert gasifier on a Ford truck converted to a tractor
During World War II gasoline was rationed and in short supply. In Great Britain, France, the United States and Germany, large numbers of such generators were constructed or improvised to convert wood and coal into fuel for vehicles. Commercial generators were in production before and after the war for use in special circumstances or in distressed economies.
FEMA Woodgas Handbook 2014-01-07
History of and the plans for making a woodgas generator