Propane, also known as liquefied petroleum gas (LPG), or propane autogas, is considered an alternative fuel under the Energy Policy Act of 1992. According to the Propane Education & Research Council, there are nearly 200,000 on-road propane vehicles with certified fuel systems in the United States. Many are used in fleet applications, such as school buses, shuttles, and police vehicles.
Propane vehicles are available from original equipment manufacturers (OEMs) or via a conversion. Propane engines and fueling systems are also available for heavy-duty vehicles, such as step vans and school buses, including some prep-ready engines from OEMs, which are included in equipment packages with components that allow conventional vehicles to run on propane.
Types of Propane Vehicles
Propane vehicles have been widely used and refined for decades. There are two types of propane vehicles: dedicated and bi-fuel. Dedicated propane vehicles are designed to run only on propane, while bi-fuel propane vehicles have two separate fueling systems that enable the vehicle to use either propane or gasoline.
A propane vehicle's power, acceleration, and cruising speed are similar to those of conventionally fueled vehicles. The driving range for dedicated and bi-fuel vehicles is also comparable. Extra storage tanks can increase range, but the tank size and additional weight affect payload capacity.
The potential for lower maintenance costs is one reason behind propane's popularity for use in light- and medium-duty vehicles, such as trucks and taxis, and for heavy-duty vehicles, such as school buses. Propane's low carbon and low oil contamination characteristics may result in longer engine life. Propane performs well in cold weather climates because the fuel's mixture (propane and air) is completely gaseous when it enters the injection system and engine. This factor allows propane-powered vehicles to avoid many cold-start issues associated with using diesel.
Bi-fuel vehicles include a secondary fuel system and fuel supply, giving them a much greater range than dedicated propane or gasoline vehicles. Likewise, larger storage tanks can increase range, but the additional weight displaces payload capacity. Because a gallon of propane has 27% less energy than a gallon of gasoline, the fuel economy of propane vehicles is slightly lower. However, propane has a higher octane rating than gasoline (104–112 compared to 87–92 for gasoline), and some OEMs offer dedicated engines optimized to take advantage of this higher rating. This can result in improved performance and fuel economy over non-optimized engines.