Producer gas is fuel gas that is manufactured from material such as coal, as opposed to natural gas. It can be produced from various fuels by partial combustion with air, usually modified by simultaneous injection of water or steam to maintain a constant temperature and obtain a higher heat content gas by enrichment of air gas with hydrogen. In this respect it is similar to other types of "manufactured" gas, such as coal gas, coke oven gas, water gas and carburetted water gas. Producer gas was used primarily as an industrial fuel for iron and steel manufacturing, such as firing coke ovens and blast furnaces, cement and ceramic kilns, or for mechanical power through gas engines. It was characteristically low in heating value but cheap to make, so that large amounts could be made and burnt.
In the USA, producer gas may be wood gas produced in a gasifier and used to fire kilns and has been used to power cars and boats, town gas, originally produced from coal, for sale to consumers, and syngas, used as a fuel source or as an intermediate for the production of other chemicals.
In the UK, producer gas, also known as suction gas, means a fuel gas made from coke, or other carbonaceous material such as anthracite. Air is passed over the red-hot carbonaceous fuel and carbon monoxide is produced. The reaction is exothermic and proceeds as follows:
Formation of producer gas from air and carbon:
- C + O2 → CO2, +97,600 calories
- CO2 + C → 2CO, -38,800 calories
- 2C + O2 → 2CO, +58,800 calories
Reactions between steam and carbon:
- H20+C → H2+CO, -28,800 calories
- 2H20+C → 2H2+CO2, -18,800 "
Reaction between steam and carbon monoxide:
- H2O + CO → CO2 + H2, + 10,000 calories
- CO2 + H2 → CO +H2O, -10,000 calories
The average composition of ordinary producer gas according to Latta was: CO2: 5.8%; O2: 1.3%; CO: 19.8%; H2: 15.1%; CH4: 1.3%; N2: 56.7%; B.T.U. gross per cu.ft 136  The concentration of carbon monoxide in the "ideal" producer gas was considered to be 34.7% carbon monoxide (carbonic oxide) and 65.3% nitrogen. After "scrubbing", to remove tar, the gas may be used to power gas turbines (which are well-suited to fuels of low calorific value), spark ignited engines (where 100% petrol fuel replacement is possible) or diesel internal combustion engines (where 15% to 40% of the original diesel fuel requirement is still used to ignite the gas ). During World War II in Britain, plants were built in the form of trailers for towing behind commercial vehicles, especially buses, to supply gas as a replacement for petrol (gasoline) fuel. A range of about 80 miles for every charge of anthracite was achieved.
In old movies and stories, when describing suicide by "turning on the gas" and leaving an oven door open without lighting the flame, the reference was to coal gas or town gas. As this gas contained a significant amount of carbon monoxide it was quite toxic. Most town gas was also odorized, if it did not have its own odor. Modern 'natural gas' used in homes is far less toxic, and has a mercaptan added to it for odor for identifying leaks.
Various names are used for producer gas, air gas and water gas generally depending on the fuel source, process or end use including:
- Air gas: a.k.a. “power gas,” “generator gas” or “Siemen’s producer gas.” Produced from various fuels by partial combustion with air. Air gas consists principally of carbon monoxide with nitrogen from the air used and a small amount of hydrogen. This term is not commonly used, and tends to be used synonymously with wood gas.
- Producer gas: Air gas modified by simultaneous injection of water or steam to maintain a constant temperature and obtain a higher heat content gas by enrichment of air gas with H2. Current usage often includes air gas.
- Semi-water gas: Producer gas.
- Blue water-gas: Air, water or producer gas produced from clean fuels such as coke, charcoal and anthracite which contain insufficient hydrocarbon impurities for use as illuminating gas. Blue gas burns with a blue flame and does not produce light except when used with a Weisbach mantle.
- Lowe’s Water Gas: Water gas with a secondary pyrolysis reactor to introduce hydrocarbon gasses for illuminating purposes. 
- Carbutetted gas: Any gas produced by a process similar to Lowe’s in which hydrocarbons are added for illumination purposes.
- Wood gas: produced from wood by partial combustion. Sometimes used in a gasifier to power cars with ordinary internal combustion engines.
Other similar fuel gasses
- Coal Gas or Illuminating gas: Produced from coal by distillation.
- Water gas: Produced by injection of steam into fuel preheated by combustion with air. The reaction is endothermic so the fuel must be continually re-heated to keep the reaction going. This was usually done by alternating the steam with an air stream. This names is sometimes used incorrectly when describing carburetted blue water gas simply as blue water gas.
- Coke Oven Gas: Coke ovens give off a gas exactly similar to illuminating gas, part of which is used to heat the coal. There may be a large excess, however, which is used for industrial purposes after it has been purified.
- syngas, or synthesis gas: (from synthetic gas or synthesis gas) can be applied to any of the above gasses, but generally refers modern industrial processes, such as natural gas reforming, hydrogen production, and processes for synthetic production of methane and other hydrocarbons.
- City (Town) gas: any of the above manufactured gases including producer gas containing sufficient hydrocarbons to produce a bright flame for illumination purposes, originally produced from coal, for sale to consumers and municipalities.
- Farmer, Weston. From My Old Boatshop, 1979 International Marine Publishing, p. 176-198
- Nisbet Latta, "American Producer Gas Practice and Industrial Gas Engineering", D. Van Nostrand Company, 1910 , page 107
- W. J. Atkinson Butterfield, "The Chemistry of Gas Manufacture, Volume 1. Materials and Processes", Charles Griffin & Company Ltd., London, 1907, page 72
- Staff (16 July 1941). "Producer gas for transport". Parliamentary Debates. Hansard. Retrieved 15 November 2008.
- Taylor, Sheila (2001). The Moving Metropolis. London: Calmann and King. p. 258. ISBN 1-85669-241-8.
- CONVERSION OF SOLID FUELS TO LOW BTU GAS Thomas E. Ban McDowell-Wellman Engineering Company Cleveland, Ohio 44110
- Proceedings of the American Gas Light Association ... By American Gas Light Association, 1881 http://books.google.com/books?id=OSNLAAAAMAAJ&pg=PA116&dq=%E2%80%9CLowe+Water+Gas+Process%E2%80%9D&hl=en&ei=MwC4TrPaH4OesQL3mK26Aw&sa=X&oi=book_result&ct=result&resnum=1&sqi=2&ved=0CDAQ6AEwAA#v=onepage&q=%E2%80%9CLowe%20Water%20Gas%20Process%E2%80%9D&f=false
- Mellor, J.W., Intermediate Inorganic Chemistry, Longmans, Green and Co., 1941, page 211
- Adlam, G.H.J. and Price, L.S., A Higher School Certificate Inorganic Chemistry, John Murray, 1944, page 309