Also known as liquefied petroleum gas (LPG) or propane autogas, propane is a clean-burning, high-energy alternative fuel that’s been used for decades to power light-, medium- and heavy-duty propane vehicles.
LPG is basically the same type of gas that is used in home barbeques. For automotive applications, it is a mixture of propane gas and butane gas.
Propane is stored onboard a vehicle in a tank pressurized to about 150 pounds per square inch—about twice the pressure of an inflated truck tire. Under this pressure, propane becomes a liquid with an energy density 270 times greater than its gaseous form. Propane has a higher octane rating than gasoline, which prevents engine knocking. However, it has a lower British thermal unit (Btu) rating than gasoline, so it takes more fuel to drive the same distance.