Natural gas powers more than 100,000 vehicles in the United States and roughly 11.2 million vehicles worldwide. Natural gas vehicles (NGVs) are most appealing to high-mileage fleets - such as buses and taxis - that are centrally fueled or operate within a limited area. The advantages of natural gas as an alternative fuel include its domestic availability, variable cost, and clean-burning qualities.
What is natural gas? Natural gas is an odorless, nontoxic, gaseous mixture of hydrocarbons - predominantly methane (CH4). Because it is a gas, it must be stored onboard a vehicle in either a compressed gaseous or liquefied state. Compressed natural gas (CNG) is typically stored in a tank at a pressure of 3,000 to 3,600 pounds per square inch. Liquefied natural gas (LNG) is super-cooled and stored in its liquid phase at -260°F in special insulated tanks. Natural gas is sold in units of gasoline or diesel gallon equivalents based on the energy content of a gallon of gasoline or diesel fuel.
How do NGV emissions compare with gasoline and diesel vehicle emissions? Compared with gasoline and diesel vehicles, NGVs can lower carbon monoxide, nitrogen oxide, non-methane hydrocarbon, particulate matter, and other toxic emissions, as well as greenhouse gas emissions. In addition, because CNG fuel systems are completely sealed, CNG vehicles produce no evaporative emissions. For details, see the Natural Gas Vehicle Emissions page in the Vehicles section of the AFDC at www.afdc.energy.gov.
Is natural gas safe for use in vehicles? Yes. NGVs meet the same safety standards as gasoline and diesel vehicles and also meet the National Fire Protection Association's (NFPA) NFPA 52 Vehicular Fuel System Code. Natural gas has a narrow flammability range and, because it is lighter than air, dissipates quickly if released. NGV fuel tanks are strong and extremely puncture resistant.