Wood gas, or wood gasification, is a decades-old renewable energy technology that converts chunks of firewood, wood chips or other cellulosic biomass to charcoal, volatile and combustible gases, and occasionally, combustible liquids.

The process, which is called pyrolysis, is accomplished by cooking the wood (under low oxygen conditions) in a wood-gas generator and collecting the vapors, which are then directed to the vehicle's (ideally a truck or SUV with room to carry the gas generator) carburetor to be burned instead of gasoline.

The principal “waste” product from this process is charcoal, which is now being studied as a valuable amendment for some soils. (To learn more, read Make Biochar — this Ancient Technique Will Improve Your Soil.)

This process was used to fuel trucks in England during World War II. Because today’s society continues to be extremely dependent upon gasoline as our primary fuel for transportation, wood gas has received research attention from the Federal Emergency Management Agency (FEMA). A report, prepared by the Oak Ridge National Laboratory, which works for the Department of Energy, provides detailed instructions for construction, installation and operation of a wood-gas generator. Download the report (NOTE: this is a 25 MB+ file and thus may not be feasible to download over a slow Internet connection) via the following link: Construction of a Simplified Wood Gas Generator for Fueling Internal Combustion Engines in a Petroleum Emergency.

The purpose of the report "is to develop detailed, illustrated instructions for the fabrication, installation, and operation of a biomass gasifier unit (that is, a "producer gas" generator, also called a "wood gas" generator) which is capable of providing emergency fuel for vehicles, such as tractors and trucks, in the event that normal petroleum sources were severely disrupted for an extended period of time. These instructions are prepared in the format of a manual for use by any mechanic who is reasonably proficient in metal fabrication or engine repair.

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This report attempts to preserve the knowledge about wood gasification as put into practical use during World War II. Detailed, step-by-step fabrication procedures are presented for a simplified version of the World War II, Imbert wood gas generator. This simple, stratified, downdraft gasifier unit can be constructed for materials which would be widely available in the United States in a prolonged petroleum crisis. For example, the body of the unit consists of a galvanized metal garbage can atop a small metal drum; common plumbing fittings are used throughout; and a large, stainless steel mixing bowl is used for the grate. The entire compact unit was mounted onto the front of a farm tractor and successfully field tested, using wood chips as the only fuel. Photographic documentation of the actual assemble of the unit as well as its operation is included."