Wood gas is a syngas fuel which can be used as a fuel for furnaces, stoves and vehicles in place of gasoline, diesel or other fuels. During the production process biomass or other carbon-containing materials are gasified within the oxygen-limited environment of a wood gas generator to produce hydrogen and carbon monoxide.
These gases can then be burnt as a fuel within an oxygen rich environment to produce carbon dioxide, water and heat. In some gasifiers this process is preceded by wood pyrolysis, where the biomass or coal is first converted to charcoal, releasing methane and tar rich in polycyclic aromatic hydrocarbons.
Wood gasification is a process whereby organic material is converted into a combustible gas under the influence of heat - the process reaches a temperature of 1,400 °C (2,550 °F).
The first use of wood gasification dates back to 1870s, when it was used as a forerunner of natural gas for street lighting and cooking.
In the 1920s, German engineer Georges Imbert developed a wood gas generator for mobile use. The gases were cleaned and dried and then fed into the vehicle's combustion engine, which barely needs to be adapted. The Imbert generator was mass produced from 1931 on.
At the end of the 1930s, about 9,000 wood gas vehicles were in use, almost exclusively in Europe.
A network of some 3,000 "petrol stations" was set up, where drivers could stock up on firewood. Not only private cars but also trucks, buses, tractors, motorcycles, ships and trains were equipped with a wood gasification unit. Some tanks were driven on wood gas, too, but for military use the Germans preferred the production of liquid synthetic fuels (made out of wood or coal).
Wood gas vehicles were used during World War II , as a consequence of the rationing of fossil fuels. In Germany alone, around 500,000 "producer gas" vehicles were in use at the end of the war. Trucks, buses, tractors, motorcycles, ships and trains were equipped with a wood gasification unit. In 1942 (when wood gas had not yet reached the height of its popularity), there were about 73,000 wood gas vehicles in Sweden, 65,000 in France, 10,000 in Denmark, and almost 8,000 in Switzerland. In 1944, Finland had 43,000 "woodmobiles", of which 30,000 were buses and trucks, 7,000 private vehicles, 4,000 tractors and 600 boats.
Wood gasifiers are still manufactured in China and Russia for automobiles and as power generators for industrial applications. Trucks retrofitted with wood gasifiers are used in North Korea in rural areas, particularly on the roads of the east coast.
Torsten Källe's charcoal gasifier was somewhat ahead of its time. It was very popular due to its easy maintenance and fuel economy. Some features of this gasifier are perhaps recognised in modern gasification technology; among many things it was a sort of predecessor to what today is called 'circulating fluidised bed.' Charcoal gasifiers were generally more popular than wood gasifiers during the producer gas era in Sweden in the days of WW2, even as the wood gasifiers improved in design. Wood gas was cheaper, but charcoal gasifiers were so much easier to handle.
Fuel gas, produced by the reduction of coal and peat, was used for heating as early as 1840 in Europe, and by 1884 it had been adapted to fuel engines in England. Petroleum shortages during World War II led to widespread gas generator applications in the transportation industries of Western Europe. (Charcoal-burning taxis, a related application, were still common in Korea as late as 1970.)
Rising fuel prices and global warming have resulted in renewed interest in firewood as a direct fuel. Dozens of amateur engineers around the world have converted standard production cars into producer gas vehicles, with most of these modern woodmobiles being built in Scandinavia.
In 1957, the Swedish government set up a research program to prepare for a fast transition to wood gas cars in case of a sudden oil shortage. Sweden has no oil reserves, but it does have vast woodlands it can use for fuel.
The goals of this research was to develop an improved, standardised installation that could be adapted for use in all kinds of vehicles.
This investigation, supported by car manufacturer Volvo, led to a great deal of theoretical knowledge and hands-on experience with several road vehicles (one seen above) and tractors over a total distance of more than 100,000 kilometres (62,000 miles). The results are summarised in a FAO document from 1986, which also discusses some experiments in other countries. Swedish and, particularly Finnish amateur engineers have used this data to further develop the technology (overview, below a vehicle of Juha Sipilä).
Wood gasifiers can power either spark ignition engines, where 100% of the normal petrol can be replaced with little change to the carburation, or in a diesel engine, feeding the gas into the air inlet that is modified to have a throttle valve, if it didn't have it already. Wood can be used to power cars with ordinary internal combustion engines if a wood gasifier is attached. This was quite popular during World War II in several European, African and Asian countries because the war prevented easy and cost-effective access to oil. In more recent times, wood gas has been suggested as a clean and efficient method to heat and cook in developing countries, or even to produce electricity when combined with an internal combustion engine.
The fuel for a wood gas car consists of wood or wood chips (see picture on the left). Charcoal can also be used, but this leads to a 50 percent loss in the available energy contained in the original biomass. On the other hand, charcoal contains more energy, so that the range of the car can be extended. In principle, any organic material can be used. During the Second World War, coal and peat were also used, but wood was the main fuel.
One of the more successful wood gas cars was built by Dutch John. While many recent producer gas vehicles seem to come straight out of Mad Max, the Dutchman's Volvo 240 is equipped with a very modern-looking system made of stainless steel
Dutch John strongly believes in wood gas generators, mainly for stationary uses such as heating, electricity generation or even the production of plastics. The Volvo is meant to demonstrate the possibilities of the technology. "Park an Italian sports car next to a wood gas car and the crowd gathers around the woodmobile. Nevertheless, wood gas cars are only for idealists and for times of crisis."
Yet, while biofuel-powered car is as user-friendly as a gasoline rival, wood gas has to be the most user-unfriendly alternative fuel that exists.
This can be an advantage: a switch to wood gas cars can only mean that we would drive less, and that would of course be a good thing from an environmental viewpoint. If you need to preheat your car for 10 minutes, chances are you will decide not to use it to drive a few miles to pick up some groceries. A bicycle would do the job faster. If you had to cut wood for three hours just to make a trip to the beach, you would probably decide to take the train.
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