Propane, also known as liquefied petroleum gas (LPG), is the most widely used alternative fuel in the United States due to its high energy density, clean burning properties, established infrastructure, and domestic availability. Propane is also the third most used vehicle fuel, behind gasoline and diesel.
A colorless and odorless liquid, propane (C3H8) is a mixture of hydrocarbons found in natural gas and is refined from crude petroleum. Propane has a high octane rating, is non-toxic, and usually less expensive than gasoline. Propane-fueled vehicles emit less carbon dioxide and fewer smog-forming air pollutants than gasoline-powered vehicles.
Propane has the lowest flammability range and one of the highest energy densities of all alternative fuels. Still, a gallon of propane has about 25 percent less energy than a gallon of gasoline.
For easier distribution, propane is liquefied through pressurization. The fuel is stored under pressure inside the tank and when pressure is released, the liquid propane vaporizes and turns into a gas that is used for combustion.
Propane is used mainly by fleets because propane vehicles have a good driving range and the gaseous state of propane eliminates cold start problems associated with liquid fuels. Propane is also popular for use in delivery trucks, taxis, and buses because of lower maintenance costs; for example, Portland school buses are fueled by propane. Propane engines have been documented to have an engine life up to two times that of gasoline engines.
Automotive engineer Roush introduced the first dedicated propane powered Ford pickup truck in 2007. The Roush F-150 LPI uses a liquid propane injection system and is designed to have the same horsepower, torque and drivability as the gasoline-powered F-150.
Gasoline and diesel vehicles can be converted to bi-fuel vehicles powered by propane and the original conventional fuel. Separate fuel systems are needed for these bi-fuel vehicles because the propane is stored in high-pressure fuel tanks. The cost of converting a light-duty vehicle from gasoline to propane ranges from $4,000 to $12,000. Upfront costs are easily offset by lower operating and maintenance costs over the lifespan of the vehicle.
