Propane, also known as liquefied petroleum gas or LPG, is considered an alternative fuel under the Energy Policy Act of 1992. There are more than 270,000 on-road propane cars in the United States and more than 10 million worldwide. Many are used in fleets, including light- and heavy-duty trucks, buses, taxicabs, police cars, and rental and delivery cars.
The availability of new light-duty original equipment manufacturer propane cars has declined in recent years. However, certified installers can economically and reliably retrofit many light-duty cars for propane operation. Propane engines and fueling systems are also available for heavy-duty cars such as school buses and street sweepers.
What is a propane car?
Propane, also known as liquefied petroleum gas (LPG), has been used in cars since the 1920s. It is considered an alternative fuel under the Energy Policy Act of 1992 and qualifies for alternative fuel car tax incentives.
Today, most propane cars are conversions from gasoline cars. Dedicated propane cars are designed to run only on propane; bi-fuel propane cars have two separate fueling systems that enable the car to use either propane or gasoline.
Propane car power, acceleration, and cruising speed are similar to those of gasoline-powered cars. The driving range for bi-fuel cars is comparable to that of gasoline cars. The range of dedicated gas-injection propane cars is generally less than gasoline cars because of the 25% lower energy content of propane and lower efficiency of gas-injection propane fuel systems. Extra storage tanks can increase range, but the additional weight displaces payload capacity. Liquid Propane Injection engines, introduced in 2006, promise to deliver fuel economy more comparable to gasoline systems.
Lower maintenance costs are a prime reason behind propane’s popularity for use in delivery trucks, taxis, and buses. Propane’s high octane rating (104 to 112 compared with 87 to 92 for gasoline) and low carbon and oil contamination characteristics have resulted in documented engine life of up to two times that of gasoline engines. Because the fuel mixture (propane and air) is completely gaseous, cold start problems associated with liquid fuel are eliminated.
Compared with cars fueled with conventional diesel and gasoline, propane cars can produce significantly lower amounts of harmful emissions. Another benefit of propane cars is increasing U.S. energy security.
How Propane Cars Work
Propane cars work much like gasoline-powered cars with spark-ignited engines. Propane is stored as a liquid in a relatively low-pressure tank (about 300 pounds per square inch). Liquid propane travels along a fuel line into the engine compartment. The supply of propane to the engine is controlled by a regulator or vaporizer, which converts the liquid propane to a vapor. The vapor is fed to a mixer located near the intake manifold, where it is metered and mixed with filtered air before being drawn into the combustion chamber where it is burned to produce power, just like gasoline.
Liquid Propane Injection engines, developed over the past 15 years, do not vaporize the propane. Instead, it is injected into the combustion chamber in liquid form. Liquid injection systems have proven reliable in terms of power, engine durability, and cold starting.
Propane Car Emissions
Compared with cars fueled with conventional diesel and gasoline, propane (also known as liquefied petroleum gas or LPG) cars can produce significantly lower amounts of some harmful emissions and the greenhouse gas carbon dioxide.
The EPA calculated the potential benefits of propane versus gasoline based on the inherently cleaner-burning characteristics of propane, summarized in Clean Alternative Fuels:
- Potentially lower toxic, carbon dioxide (CO2), carbon monoxide (CO), and nonmethane hydrocarbon (NMHC) emissions.
- Rich calibration shows high NMHC and CO emissions, but lower nitrogen oxide (NOx) emissions
- Lean calibration shows slightly higher NOx emissions, but lower CO and NHMC emission
