Natural gas fuels changes in transit systems

Gasoline vehicles and the infrastructure needed to fuel them are a significant source of air pollution in the United States. Gasoline-powered cars, vans, trucks and buses contribute about three-fourths of the carbon monoxide pollution found in urban areas. They also produce most of the hydrocarbons and a significant amount of nitrogen oxides as well. These gases, when combined in the presence of sunlight, form ground-level ozone or smog. More than 51 million Americans live in counties that have unhealthy ground-level ozone levels, according to a 1993 U.S. Environmental Protection Agency (EPA) report.

One way metropolitan areas are tackling air pollution, according to the American Gas Association (AGA), Arlington, Va., is by increasing the use of natural gas vehicles (NGV), which emit 85 percent to 90 percent less carbon monoxide and reactive hydrocarbons and 32 percent less carbon dioxide than conventionally fueled vehicles.

More than 33,000 NGVs were on the road in 1993, according to the U.S. Department of Energy, with thousands added each year. More than 1,000 natural gas fueling stations are available nationwide. Several federal initiatives recognize the environmental benefits of NGVs and other alternative-fuel vehicles. The Clean Air Act Amendments of 1990 (CAAA) encouraged the owners of fleets of public and private vehicles, as well as urban mass transit buses, to use alternative fuels.

The city of New York operates the largest and most diverse municipal fleet of NGVs in the United States with more than 600 natural gas-powered cars, trucks, vans and transit buses in use. The Department of Sanitation operates 108 NGVs, including seven garbage trucks and two street sweepers.

The Department of Transportation, in addition to operating 71 light-duty NGVs, purchased 53 dedicated natural gas buses that serve routes in Brooklyn, Queens and Manhattan. An additional 36 natural gas buses are scheduled to be delivered during the year.

Vehicles that run on natural gas can be factory-built or converted from conventional vehicles. NGVs can operate in three different modes: on natural gas only (“dedicated” vehicles), on either natural gas or gasoline at the flip of a switch (“bi-fuel” vehicles) or on natural gas and diesel fuel at the same time (“dual-fuel”).

The best performance is achieved when a vehicle is dedicated to run only on natural gas, because the engine can then be set to take full advantage of the fuel’s 120+ octane. In bi-fuel vehicles, a simple electronic timing device is used to adjust the engine to operate properly for each fuel. In a dual-fuel vehicle, combustion of diesel fuel serves to ignite the natural gas.

Two methods of natural gas fueling are available: fast-fill and time-fill. With fast-fill, vehicles can be fueled in about the same amount of time it takes to fuel a vehicle with gasoline or diesel. The time-fill system is designed for centrally fueled fleets and can take several minutes or several hours, depending on the number of vehicles being fueled at the same compressor station.

About 88 percent of the natural gas used in the United States is produced here, and the rest comes from Canada and Mexico. The fueling infrastructure for natural gas vehicles is expanding rapidly.

By the end of 1994, more than 900 natural gas refueling stations were operating in 46 of the lower 48 states and the District of Columbia. Three to four more open every week.

Natural gas as a vehicle fuel costs approximately 40 percent to 50 percent less than gasoline for the energy equivalent of a gallon. As a result, fleet owners or individuals who convert existing vehicles to natural gas can recoup the costs of conversion through fuel savings.

In addition to paying less for fuel, natural gas vehicle owners save money through a reduction in routine maintenance.

Because natural gas does not foul combustion chambers as does gasoline, NGVs need fewer spark plug and oil changes.