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A wood gas generator is a gasification unit which converts timber or charcoal into
wood gas Wood gas is a fuel gas that can be used for furnaces, stoves, and vehicles. During the production process, biomass or related carbon-containing materials are gasified within the oxygen-limited environment of a wood gas generator to produce a c ...
, a producer gas consisting of atmospheric
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
,
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
,
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
, traces of
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
, and other gases, which – after cooling and filtering – can then be used to power an
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal c ...
or for other purposes. Historically wood gas generators were often mounted on
vehicle A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses, mobility scooters for disabled people), railed vehicles (trains, trams), ...
s, but present studies and developments concentrate mostly on stationary plants.


History


Origins

Gasification was an important and common technology during the 19th and early 20th century.
Town gas Coal gas is a flammable gaseous fuel made from coal and supplied to the user via a piped distribution system. It is produced when coal is heated strongly in the absence of air. Town gas is a more general term referring to manufactured gaseous ...
produced from coal was widely used, mainly for lighting purposes. When stationary
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal c ...
s based on the
Otto cycle An Otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical spark ignition piston engine. It is the thermodynamic cycle most commonly found in automobile engines. The Otto cycle is a description of what hap ...
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 A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A ...
expired in 1886. The potential and practical applicability of gasification to
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal c ...
s 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 Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
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 commonly 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. During
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...
,
gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organi ...
was rationed and in short supply. Due to the lack of gasoline from petroleum, older people recalled how to build gasifiers for both wood and coal, and how to convert internal combustion engines to run on gaseous fuel, and wood gas generators were in active production. 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. Some World War II era wood gas generators were of the "Imbert" downdraft type, designed around 1920 by French inventor
Georges Imbert Georges Christian Peter Imbert (26 March 1884 – 6 February 1950) was a French chemical engineer and inventor. He became famous for the invention of the wood gas generator.''The Biofuels Handbook.'' Author: James G Speight. Royal Society of ...
. Germany produced Gazogene units for vehicles including cars, trucks, artillery tractors and even tanks, to preserve the limited supplies of fuel. Even in non-combatant countries, such as Sweden or
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
, gasogene was popular, as oil became hard to obtain. In Brazil, a racer named
Chico Landi Francisco Sacco Landi (July 14, 1907 – June 7, 1989), better known as Chico, was a racing driver from São Paulo, Brazil. He participated in six Formula One World Championship ''Grands Prix'', debuting on September 16, 1951. He scored a to ...
won at
São Paulo São Paulo (, ; Portuguese for ' Saint Paul') is the most populous city in Brazil, and is the capital of the state of São Paulo, the most populous and wealthiest Brazilian state, located in the country's Southeast Region. Listed by the Ga ...
's
Interlagos Interlagos is a neighborhood located in the district of Socorro in the city of São Paulo, Brazil. Its name comes from the fact that the region is located between two large reservoirs, Guarapiranga and Billings, built in the early 20th century ...
circuit in 1944, driving a wood gas-powered Alfa Romeo. Coal-based town gas production was generally displaced by petroleum-based gas and natural gas. However, Great Britain continued her use of coal-based town gas until the
North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea, epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the ...
natural gas discoveries in the 1960s and 1970s. Image:Adler Diplomat 3 GS mit Holzgasgenerator-hinten rechts.JPG, Adler Diplomat in WWII with wood gas generator File:Wood gasifier on epa tractor.jpg, Imbert gasifier on a
Ford Ford commonly refers to: * Ford Motor Company, an automobile manufacturer founded by Henry Ford * Ford (crossing), a shallow crossing on a river Ford may also refer to: Ford Motor Company * Henry Ford, founder of the Ford Motor Company * Ford F ...
truck converted to a tractor, Per Larssons Antique Tractor Museum, Sweden, 2003 File:1956 Citroen 11BL Traction Avant Gasogene at PB 2022.jpg, alt=Demonstration of a working "gasogene" system in a 1956 Citroën Traction Avant, Demonstration of a working Gohin-Poulenc "gasogene" system in a 1956 Citroën Traction Avant


Post World War II

When oil prices rose there was renewed interest in wood gas generators. The US
Federal Emergency Management Agency The Federal Emergency Management Agency (FEMA) is an agency of the United States Department of Homeland Security (DHS), initially created under President Jimmy Carter by Presidential Reorganization Plan No. 3 of 1978 and implemented by two Ex ...
(FEMA) published a book in March 1989 describing how to build a gas generator in an emergency when oil was not available. It described a design called the "stratified downdraft gasifier" which solves several drawbacks of earlier types. The
European Union The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been de ...
sponsored a wood gas project in Güssing, Austria, starting in 2005. This project was an electric power plant with a wood gas generator and a gas engine to convert the wood gas into 2  MW electric power and 4.5 MW heat. There was also an experimental device to use the
Fischer–Tropsch process The Fischer–Tropsch process is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen, known as syngas, into liquid hydrocarbons. These reactions occur in the presence of metal catalysts, typically at temperatu ...
to convert wood gas to a diesel-like fuel. By October 2005, it was possible to convert 5 kg of wood into 1 litre of fuel. The Democratic People's Republic of Korea (North Korea) is also known to have trucks that run off of wood gas generators. The trucks are common outside of
Pyongyang Pyongyang (, , ) is the capital and largest city of North Korea, where it is known as the "Capital of the Revolution". Pyongyang is located on the Taedong River about upstream from its mouth on the Yellow Sea. According to the 2008 populat ...
and are in rural villages and smaller towns. These trucks are utilized due to sanctions placed on North Korea regarding imports of oil and gas.


Design

There is a rich literature on gas-works, town-gas, gas-generation, wood-gas, and producer gas, that is now in the public domain due to its age. Most successful wood gas generators in use in Europe and the United States are some variation of the earlier Imbert design. Wood gas generators often use wood; however, charcoal can also be used as a fuel. It is denser and produces a cleaner gas without the tarry volatiles and excessive water content of wood. The FEMA wood gas generator is (by definition of the FEMA manual) an emergency gasifier. It is designed to be rapidly assembled in a true fuel crisis. This simplified design has distinct benefits over the earlier European units such as easier refueling and construction but is less popular than the earlier Imbert design because of significant new problems, which include a lack of a fixed oxidization zone and allows the oxidization zone to creep to a larger area, causing a drop in temperature; a lower operating temperature leads to
tar Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat. "a dark brown or black bi ...
production and it lacks a true reduction zone further increasing this design's propensity to produce tar. Tar in the wood gas stream is considered a dirty gas and tar will gum up a motor quickly, possibly leading to stuck valves and rings. A new design known as the Keith gasifier improves on the FEMA unit, incorporating extensive heat recovery and eliminating the tar problem. Testing at Auburn University has shown it to be 37% more efficient than running gasoline. This system set the world speed record for biomass powered vehicles and has made several cross country tours. The United Nations produced the FOA 72 document with details about their wood gas generator design and construction, as does World Bank technical paper 296.


Advantages

Wood gas generators have a number of advantages over use of
petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...
fuels: *They can be used to run
internal combustion engines An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combust ...
(or gas turbines, for maximal efficiency) using wood, a
renewable resource A renewable resource, also known as a flow resource, is a natural resource which will replenish to replace the portion depleted by usage and consumption, either through natural reproduction or other recurring processes in a finite amount of ti ...
, and in the absence of petroleum or
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
, for example, during a fuel shortage. *They have a closed
carbon cycle The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major componen ...
, contribute less to
global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
, and are sustainable in nature. *They can be relatively easily fabricated in a crisis using materials on hand. *They are far cleaner burning than a wood fire or a gasoline-powered engine (without emissions controls), producing little, if any soot. *When used in a stationary design, they reach their true potential, as they are feasible to use in small combined heat and power scenarios (with heat recovery from the wood gas producer, and possibly the engine/generator, for example, to heat water for
hydronic heating Hydronics () is the use of liquid water or gaseous water (steam) or a water solution (usually glycol with water) as heat-transfer medium in heating and cooling systems. The name differentiates such systems from oil and refrigerant systems. ...
), even in industrialized countries, even during good economic times, provided that a sufficient supply of wood is attainable. Larger-scale installations can reap even better efficiencies, and are useful for
district heating District heating (also known as heat networks or teleheating) is a system for distributing heat generated in a centralized location through a system of insulated pipes for residential and commercial heating requirements such as space heating a ...
as well.


Disadvantages

The disadvantages of wood gas generators are: *the large specific size *the relatively slow starting speed; the time to heat the initially cold batch of wood to the necessary temperature level can take many minutes and in bigger plants even hours until the designed power is reached. *a batch burning operation, that some designs feature, and that regularly interrupts the gas producing process. *the stop operation out of a high load level is difficult (for example the stop of the engine using the gas): the residual heat still produces gas, which for a certain time leaves the gasifier either without control, or has to be used in a burner *the primary combustible fuel-gas produced during gasification is
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
: it is an intentional fuel-product, and is subsequently burned to safe
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
in the engine (or other application) along with the other fuel-gases; however, continuous exposure to carbon monoxide can be fatal to humans even in small to moderate concentrations. *the
humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity dep ...
of the wood (usually 15 to 20%) and the
water vapor (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/( kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Heat capacity , 1.864 kJ/(kg·K) Water vapor, water vapour or aqueous vapor is the gaseous p ...
created by the O- and H-atoms of the dry wood itself (about 0.4 liters of water loaded with organic substances per kg of dry wood) condenses during the gas cooling and filtering procedure and yields a liquid (see also
wood tar Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat. "a dark brown or black bi ...
), which needs specific
waste water Wastewater is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of domestic, industrial ...
treatment. This treatment requires about 25 to 35% of the created wood gas energy.


Safety consideration

When not carefully designed and used, there exists considerable potential for injury or death due to wood gas containing a large percentage of poisonous
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
(CO) gas. Wood gasifiers of proven design and thoroughly tested construction are considered safe to use outdoors, or in a partially enclosed space, for example, under a shelter open to the air on two sides; they may also be considered relatively safe to use in an extremely well ventilated (e.g.
negative pressure Negative pressure may refer to: * Negative value of a pressure variable * Negative room pressure, a ventilation technique used to avoid contaminating outside areas * Negative pressure ventilator, also known as an iron lung * Negative-pressure wou ...
) indoor area not connected to any indoor area used for sleeping, equipped with redundant (more than 1), completely independent, battery-powered, regularly tested carbon-monoxide
gas detector A gas detector is a device that detects the presence of gases in an area, often as part of a safety system. A gas detector can sound an alarm to operators in the area where the leak is occurring, giving them the opportunity to leave. This type of ...
s. However, prudence must dictate that any sort of experimental wood gasifier design or new construction be thoroughly tested outdoors, and only outdoors, with a "buddy" at all times, and with constant vigilance for any sign of headache, drowsiness, or nausea, as these are the first symptoms of carbon monoxide poisoning. In addition, mixtures of excessive quantities of air and gas should be avoided as this could lead to the deflagration (explosion) of the gas in question if a combustion source is present. Long-term storage of wood-gas, except through the use of a
gasholder A gas holder or gasholder, also known as a gasometer, is a large container in which natural gas or town gas is stored near atmospheric pressure at ambient temperatures. The volume of the container follows the quantity of stored gas, with pressu ...
-type water-displacement apparatus, should not be attempted, due to the volatile elements present in the gas, which, if allowed to excessively precipitate, will condense in the storage vessel. Under no circumstances should wood-gas ever be compressed to more than above ambient, as this may induce condensation of volatiles, as well as lead to the likelihood of severe injury or death due to carbon monoxide or deflagration if the vessel leaks or fails.


Media coverage

In 2008, an example of designing and constructing a working wood gas generator powered truck was shown on the National Geographic Channel's '' Planet Mechanics'' in the eighth episode, "Tree Powered Car". In 2009, another example of designing and constructing a working wood gas powered generator engine was in the TV series '' The Colony'' in the second episode of the first season "Power Struggle". Also used in the tenth episode "Exodus" to power an escape vehicle. A 2010,
Mother Earth News ''Mother Earth News'' is a bi-monthly American magazine that has a circulation of 500,520 . It is published in Topeka, Kansas. Since its founding, ''Mother Earth News'' has promoted renewable energy, recycling, family farms, good agricultural ...
article discussed and showed pictures of a wood gas powered engine installed in a pickup truck. As part of the BBC science series "Bang Goes The Theory", a Volkswagen Scirocco was converted to a design by Martin Bacon to run on
used coffee grounds Used coffee grounds is the result of brewing coffee, and are the final product after preparation of coffee. Despite having several highly-desirable chemical components, used coffee grounds are generally regarded as waste, and they are usually t ...
, and after its build in 2010 was driven solely on coffee from London to Manchester successfully. Part of the team are now working on a more advanced design leaning towards top speed as opposed to range. On September 14, 2011, at the
Bonneville Salt Flats The Bonneville Salt Flats are a densely packed salt pan in Tooele County in northwestern Utah. A remnant of the Pleistocene Lake Bonneville, it is the largest of many salt flats west of the Great Salt Lake. It is public land managed by the Bur ...
a truck modified with a wood gas powered engine set a new world speed record for vehicles powered by wood gas with a speed of 73 mph. On the popular US radio program ''
Car Talk ''Car Talk'' is a radio talk show that was broadcast weekly on National Public Radio (NPR) stations and elsewhere. Its subjects were automobiles and automotive repair, often discussed humorously. It was hosted by brothers Tom and Ray Maglioz ...
'', a caller in episode 1201 (which aired on January 7, 2012, and was subsequently named "20 Miles Per Woodchip"), described a wood gas generating vehicle he rode in as a boy during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...
in Germany. The hosts were not familiar with the technology, likely because it was never widely adopted in the US. On March 12, 2012, on a season 2 episode of Doomsday Preppers, a wood gas generator is shown running a Ford truck and a house electric generator by prepper Scott Hunt on his multi-acre woodland property in South Carolina. Serbian TV sitcom "Truckdrivers 2" (="Kamiondzije II") from 1983. talks, as a part of plot, about a gas generator affixed to a chassis of a lorry. An article appeared in
Mother Earth News ''Mother Earth News'' is a bi-monthly American magazine that has a circulation of 500,520 . It is published in Topeka, Kansas. Since its founding, ''Mother Earth News'' has promoted renewable energy, recycling, family farms, good agricultural ...
in April 2012 featuring the Keith gasifier, showing pictures and talking with inventor Wayne Keith. In the BBC documentary Wartime Farm, Episode 5 (aired October 2012) they built a coal gas powered ambulance according to the specifications of a 1943 gas powered vehicle. In Season 3 Of
Mountain Men A mountain man is an explorer who lives in the wilderness. Mountain men were most common in the North American Rocky Mountains from about 1810 through to the 1880s (with a peak population in the early 1840s). They were instrumental in opening up ...
On The History Channel, Eustice Conway is shown operating a wood gasified Toyota pickup for hauling goods The Finnish prime minister
Juha Sipilä Juha Petri Sipilä (; born 25 April 1961) is a Finnish politician who served as Prime Minister of Finland from 2015 to 2019. A relative newcomer to politics, he has a successful background in business. He was the leader of the Centre Party fr ...
has received some media attention also for the wood gas powered car he built as a hobby prior to his political career. The "El Kamina", model year 1987
Chevrolet El Camino The Chevrolet El Camino is a coupé utility vehicle that was produced by Chevrolet between 1959–60 and 1964–1987. Unlike a standard pickup truck, the El Camino was adapted from the standard two-door Chevrolet station wagon platform and integ ...
, is the fastest wood-gas powered car, 140 km/h, 87 mph.


List of commercially available systems

There are only a few companies that produce wood gasifier systems commercially. A list can be found here below. Since wood gas systems have the tendency of being rather large, most focus on stationary applications (electricity production). Some may be suitable for building into vehicles though. * Ankur Scientific Energy Technologies * GASEK * Holzenergie Wegscheid GmbH * Entrade Energiesysteme AG *
Vulcan Gasifier LLC Vulcan may refer to: Mythology * Vulcan (mythology), the god of fire, volcanoes, metalworking, and the forge in Roman mythology Arts, entertainment and media Film and television * Vulcan (''Star Trek''), name of a fictional race and their home p ...
* Victory Gasworks * Garringer Gasifier * ALL Power Labs * Husk Power Systems * STAK Properties LLC * Foutch Manufacturing * Community Power Corporation * Gasógenos GADA * REP Renewable Energy Products GmbH * Gasification Australia Pty Ltd * International Supply Biz * Borealis Wood Power Corp * Zhengzhou Shuliy Machinery Co., Ltd * Volter * Burkhardt GmbH * Spanner Re² GmbH * MRC Green * Associated Engineering Works * National innovation Foundation – India, * Trillion Gasifiers * Northern Self Reliance * Superior Gasification * Creeco (Pvt) Ltd., Pakistan * Tactical Wood Gas Inc * SynCraft Engineering GmbH


See also

*
Engine-generator An engine–generator is the combination of an electrical generator and an engine (prime mover) mounted together to form a single piece of equipment. This combination is also called an ''engine–generator set'' or a ''gen-set''. In many contexts ...
; can be connected to the gasifier on a wood gas car via a wood gas hose, hereby also being able to produce power when the vehicle's engine isn't running, in effect forming a
vehicle-to-grid Vehicle-to-grid (V2G), also known as Vehicle-to-home (V2H) or Vehicle-to-load (V2L) describes a system in which plug-in electric vehicles (PEV) sell demand response services to the grid. Demand services are either delivering electricity or by red ...
system * Exhaust heat exchanger: can be used to help heat the wood gasifier, increasing gas output of the wood gasifier * Hot air engine: similarly to the stirling engine, can use heat directly and can run on wood *
Stirling engine A Stirling engine is a heat engine that is operated by the cyclic compression and expansion of air or other gas (the ''working fluid'') between different temperatures, resulting in a net conversion of heat energy to mechanical work. More specif ...
: another engine that can use heat from wood, rather than needing to convert it to wood gas firstStirling engine animation
/ref>


References


Further reading

* "Holzbrenner Strength through Joy Wagon" (
Volkswagen Beetle The Volkswagen Beetle—officially the Volkswagen Type 1, informally in German (meaning "beetle"), in parts of the English-speaking world the Bug, and known by many other nicknames in other languages—is a two-door, rear-engine economy car, ...
, 1940–1945)


External links


2 schematics of the most common downdraft generator systemsp93; full downdraft generator systemWoodgas powered trucks and cars in the United States
{{DEFAULTSORT:Wood Gas Generator Engine technology Biogas technology Fuel gas Wood fuel Pyrolysis