Liquid Petroleum Gas (LPG or LP Gas) is a mixture of hydrocarbon gases used as a fuel in heating appliances and vehicles, and increasingly replacing fluorocarbons as an aerosol propellant and a refrigerant to reduce damage to the ozone layer. The gases are a mix of propane and butane usually with propylene and butylenes present in small concentration. A powerful odorant, ethyl mercaptan, is added to these so that leaks can be detected easily. LPG is manufactured during the refining crude oil, or extracted from oil or gas streams as they emerge from the ground.
It becomes liquid at room temperature at 6 bar pressure, so it is supplied in pressurised steel bottles. These are usually filled to 85% of their capacity with the liquified gas to provide room for the gas to expand if the bottle gets hot. The liquified gas has an expansion ratio of about 250:1.
LPG 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 in the United States.
LPG or 'Autogas' is widely used as 'green fuel' for car engines as it decreases exhaust emissions. It has a RON of 110 and an energy content of 95475 BTU/gallon.