Liquefied petroleum gas
Liquified Petroleum Gas (also called Liquefied Petroleum Gas, 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. Varieties of LPG bought and sold include mixes that are primarily propane, mixes that are primarily butanes, and mixes including both propane and butanes. Propylene and butylenes are usually also present in small concentration. A powerful odorant, ethanethiol, is added so that leaks can be detected easily. LPG is manufactured during the refining of crude oil, or extracted from oil or gas streams as they emerge from the ground.
The pressure at which LPG becomes liquid, called its vapor pressure, varies depending on composition and temperature; for example, it is approximately 2.2 bar for pure butane at 70 degrees Fahrenheit, and approximately 22 bar for pure propane at 130 degrees Fahrenheit. Because of this, LPG 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 ratio between the volumes of the liquified gas and the vaporised gas again varies depending on composition, pressure and temperature, but is typically around 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 internal combustion engines as it decreases exhaust emissions. It has a RON that is between 90 and 110 and an energy content (HHV) that is between 25.5 megajoule/liter (for pure propane) and 28.7 megajoule/liter (for pure butane.) Toyota made a number of LPG engines in their 1970s M, R, and Y engine families.
Currently, a number of automobile manufacturers -Citroën, Daewoo, Fiat, Ford, Hyundai, Opel/Vauxhall, Peugeot, Renault, Saab and Volvo- have OEM bi-fuel models that will run equally well on both LPG and petrol.
LPG as cooking fuel
According to the 2001 Census of India, 17.5% of Indian households or 33.6 million Indian households used LPG as cooking fuel in 2001. [1] 76.64% of such households were from urban India making up 48% of urban Indian households as compared to a usage of 5.7% only in rural Indian households. LPG is subsidised by the government. Increase in LPG prices has been a politically sensitive matter in India as it potentially affects the urban middle class voting pattern.
LPG was once a popular cooking fuel in Hong Kong; however, the continued expansion of town gas to buildings has reduced LPG usage to less than 24% of residential units.