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The lack of delivery infrastructure may delay the broad acceptance of natural gas as a vehicle fuel. Photo: Clean Energy
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    Liquefied natural gas can be delivered and stored like diesel, but compressed natural gas usually requires compression, storage and dispensing equipment. For a more maps, visit the Natural Gas Vehicle Institute at www.ngvi.com or the Alternative Fuel Vehicle Institute at www.afvi.org. Source: U.S. Department of Energy Alternative Fuels and Advanced Vehicles Data Center

Cities and counties have tapped into opportunities made possible through the Department of Energy's State Energy Program, which provides grants to energy offices and sponsors much of the department's Clean Cities program though its Special Projects division. In Texas, it's paid for backup compressors for the natural-gas fueling stations operated by the cities of Lake Jackson and Austin. West Virginia gives local governments grants to offset the higher sticker prices of alternatively fueled vehicles.

This year, State Energy Program appropriations totaled $50 million, which was divided evenly between competitive and formula grants. So far, $7 million of the competitive amount has been awarded. The department has asked for another $50 million for 2009.

The federal government's goal is to reduce the nation's carbon footprint. With programs spread across various departments, figuring out how to pay for greening your fleet is a matter of identifying other public agencies that would benefit and calculating the overall reduction in pollution.

So while the initial investment for natural gas is larger than for diesel vehicles, at $2.60/gallon-equivalent or less, the savings on fuel and the positive public relations benefits may outweigh the disadvantages.

— Paul Abelson is a former director of the Technology and Maintenance Council of the American Trucking Association, a board member of Truck Writers of North America, and active in the Society of Automotive Engineers.

Same style, different color

Light- and some heavy-duty natural-gas vehicles work like gasoline vehicles: with spark-ignited engines. Some heavy-duty vehicles use high-pressure direct-injection engines that burn the natural gas in a compression-ignition (diesel) cycle, but additional spark ignition is needed to sustain combustion.

Here's how a vehicle running on compressed natural gas (CNG) works:

Gas enters the vehicle through the fill valve (A) and flows into high-pressure cylinders (B). When the engine needs power, the gas leaves the cylinders and passes through the master manual shut-off valve (C), travels through the high-pressure fuel line (D), and enters the engine compartment. It then enters the regulator (E), which reduces the pressure used for storage (up to 3,600 psi) to the required fuel-injection system pressure. The solenoid valve (F) allows the gas to pass from the regulator into the mixer or fuel injectors and shuts off the flow when the engine isn't running. Gas mixed with air flows down through the fuel-injection system (G) and enters the engine combustion chambers where, like gasoline, it is burned to produce power.

Source: U.S. Department of Energy Alternative Fuels and Advanced Vehicles Data Center