The Lost Knowledge column explores the possible technology of the future in the forgotten ideas of the past (and those just slightly off to the side). We look at retro-tech, “lost” technology, and the make-do, improvised “street tech” of village artisans and tradespeople from around the globe. “Lost Knowledge” was also the theme of MAKE Volume 17
So, when that hole in the Gulf of Mexico is finished vomiting up all of its oil, the world’s oceans are dead, and we’re plunged into a Mad Max-like post-apocalypse (zombie hordes, optional), we’re going to be looking for additional sources of energy to power our machine gun-equipped technicals. Hey, how about wood gas?
What is wood gas? Sayeth Wikipedia:
“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. It is the result of two high-temperature reactions (above 700 Â°C (1,292 Â°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.”
Image of a vintage wood gas auto from 1946. From Low Technology Magazine.
Vehicles powered by wood gasification reached their peak in Europe, during WWII, largely due to gasoline rationing. There were even wood gas stations (allegedly some 3,000 of them) where wood gas vehicles could stock up on firewood. One of the great benefits of wood gas is that there’s almost no changes required to switch over an internal combustion engine normally run on gasoline. The drawbacks are not inconsiderable, including the amount of space and weight taken up by the gasification unit, and the need to carry (or acquire) the wood fuel.
Image of Dutch John’s Volvo 240 with modern wood plant on the back. From Low Technology Magazine.
Low Technology Magazine has an excellent overview article on wood gas vehicles. Here’s an excerpt:
The advantages of wood gas cars
The greatest advantage of producer gas vehicles is that an accessible and renewable fuel can be used directly without any previous treatment. Converting biomass to a liquid fuel like ethanol or biodiesel can consume more energy (and CO2) than the fuel delivers. In the case of a wood gas car, no further energy is used in producing or refining the fuel, except for the felling and cutting of the wood. This means that a woodmobile is practically carbon neutral, especially when the felling and cutting is done by hand.
Moreover, a wood gas car does not require a chemical battery, and this is an important advantage over an electric car. All too often, the embodied energy of the latter’s enormous battery is forgotten. In fact, in the case of a producer gas vehicle, the wood behaves like a natural battery. There is no need for high-tech recycling: the ash that remains, can be used as a fertilizer.
A properly-operating wood gas generator also produces less air pollution than a gasoline or diesel powered car. Wood gasification is considerably cleaner than wood burning: emissions are comparable to those of burning natural gas. An electric car has the potential to do better, but then the energy it uses should be generated by renewable sources, which is not a realistic scenario.
The drawbacks of wood gas cars
In spite of all these advantages, it takes just one look at a woodmobile to realize that it is anything but an ideal solution. The mobile gas factory takes up a lot of space and can easily weigh a few hundred kilograms – empty. The size of the equipment is due to the fact that wood gas has a low energy content. The energetic value of of wood gas is around 5.7 MJ per kg, compared to 44 MJ/kg for gasoline and 56 MJ/kg for natural gas (source).
Furthermore, the use of wood gas limits the output of the combustion engine, which means that the speed and acceleration of the converted car are cut. Wood gas consists roughly of 50 percent nitrogen, 20 percent carbon monoxide, 18 percent hydrogen, 8 percent carbon dioxide and 4 percent methane. Nitrogen does not contribute to the combustion, while coal monoxide is a slow burning gas. Because of this high nitrogen content, the engine receives less fuel, which leads to a 35 to 50 percent lower output. Because the gas burns slowly, a high number of revolutions is not possible. A producer gas vehicle is no sports car.
Even though some smaller cars have been equipped with wood gas generators (see for instance this Opel Kadett), the technology is better suited to a larger, heavier car with a powerful engine. If not, engine output and range might not be sufficient. Even though the installation can be made smaller for a smaller vehicle, its size and weight do not decrease proportionately with the decreasing size and weight of the car. Some have built wood gas-powered motorcycles, but their range is limited (a motorcycle with sidecar does better, though). Of course, the weight and size of the mobile gas factory is less an issue with buses, trucks, trains or ships.
While there isn’t huge active push for wood gas as a significant fuel source for vehicles, like all vintage and sidestream technologies, it has its champions and those who enjoy tinkering with it. See a bunch of projects linked off from the resources below.
Wood gas resources:
Wood gas vehicles: firewood in the fuel tank (Low-Tech Magazine piece)
Welcome to the magical world of wood gasification! (Dutch John’s site)
Wood gas (Wikipedia entry)
GEK Wiki (wood gasification wiki)
Woodgas.net (popular wood gas site)
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