Liquefied Petroleum Gas (also called LPG, GPL, LP Gas, or autogas) is a flammable mixture of hydrocarbon gases used as a fuel in heating appliances and vehicles, and increasingly replacing chlorofluorocarbons as an aerosol propellant and a refrigerant to reduce damage to the ozone layer.
Varieties of LPG bought and sold include mixes that are primarily propane, mixes that are primarily butane, and - most common - mixes including both propane C3H8 and butane C4H10, depending on the season — in winter more propane, in summer more butane. Propylene and butylenes are usually also present in small concentration. A powerful odorant, ethanethiol, is added so that leaks can be detected easily. The international standard is EN 589. In the United States, thiophene or amyl mercaptan are also approved odorants.
LPG is a low-carbon-emitting hydrocarbon fuel available in rural areas, emitting 81% of the CO2 per kWh produced by oil, 70% of that of coal, and less than 50% of that emitted by coal-generated electricity distributed via the grid. Being a mix of propane and butane, LPG emits less carbon per joule than butane but more carbon per joule than propane. As a low-carbon, low-polluting fossil fuel, LPG is recognised by governments around the world for the contribution it can make towards improved indoor and outdoor air quality and reduced greenhouse gas emissions. LPG is widely available and can be used for hundreds of commercial and domestic applications. LPG is also used alongside renewable technologies, as well as with decentralized electricity generation (Combined heat and power systems — See Uses - Rural heating) to help reduce carbon emissions on a local level.
LPG is synthesised by refining petroleum or wet natural gas, and is usually derived from fossil fuel sources, being manufactured during the refining of crude oil, or extracted from oil or gas streams as they emerge from the ground. It was first produced in 1910 by Dr. Walter Snelling, and the first commercial products appeared in 1912. It currently provides about 3% of the energy consumed, and burns cleanly with no soot and very few sulfur emissions, posing no ground or water pollution hazards. LPG has a typical specific calorific value of 46.1 MJ/kg compared with 42.5 MJ/kg for fuel-oil and 43.5 MJ/kg for premium grade petrol (gasoline). However, its energy density per volume unit of 26 MJ/l is lower than either that of petrol or fuel-oil.