Natural-gas VehiclesKermit the Frog once said, "It's not that easy bein' green." Although

Natural-gas Vehicles

Kermit the Frog once said, "It's not that easy bein' green." Although he wasn't referring to cars, his observation seems particularly appropriate for the auto industry today: Designing, developing and marketing "green" cars has not been an easy task, which is why gasoline-powered vehicles still rule the mad and fossil fuels still account for almost 75 percent of the word's energy consumption. As gasoline soar and concern over harmful emission mounts, however, cars that run on alternate fuel sources will become increasingly important. A natural-gas vehicle, or NGV, is the perfect example of such a car -- it's fuel- efficient, environmentally friendly and offers a relatively low cost of ownership.

Natural Gas Basics

The word "gas" is a confusing term because it is used to 'describe many different substances that are similar but not exactly the same. For example, the "gas" you put in your car is gasoline, one component of crude oil, or petroleum. Petroleum is a dark, sticky liquid mixture of compounds formed underground by the decay of ancient marine animals.

Natural gas also comes from the decay of ancient organisms, but it naturally takes a gaseous form. instead of a liquid from. Natural gas commonly occurs in association with crude oil. It is derived from both land plants and aquatic(水生的)organic matter and forms above or below oil deposits. It is often dissolved in crude oil at the high pressures existing in a reservoir. There are also reservoirs of natural gas, known as non-associated gas, that contain only gas and no oil.

Natural gas consists primarily of methane (沼气)and other hydrocarbon gases. Hydrocarbons are organic compounds composed only of the elements carbon and hydrogen. The hydrocarbons in natural gas are called saturated hydrocarbons because they contain' hydrogen and carbon bound together by single bonds.

Like gasoline, natural gas is combustible (易燃的), which means it can be used in a combustion engine like gasoline. But cars that could burn natural gas didn't appear on the scene until the 1930s.

From Field to Ford

We extract natural gas trapped in underground reservoirs by drilling wells into the earth. A modern well, equipped with diamond-studded drill bits, can drill to depths approaching 25,000 feet.

Throughout the 19th century, the use of natural gas remained localized because there was no way to transport large quantities of gas over long distances. In 1890, the invention of a leakproof pipeline coupling made it possible to transport gas miles from the source. Improvements in pipeline technology continued over the next two decades until long-distance gas transmission became practical. From 1927 to 1931, laborers constructed more than 10 major natural gas transmission systems in the United States, making natural gas a viable energy source for many applications. The oil shortages of the late 1960s and early 1970s brought renewed interest in natural gas as a fuel source, especially for automobiles.

Today, owners of natural-gas vehicles can fill up their cars at one of 1,300 fueling stations located in the United States. Honda also offers a personal natural gas pump to people who purchase its natural-gas- powered Civic. The pump uses a home's existing natural gas lines and can be installed for $ 500 to $ 1, 500.

Natural-gas Vehicle Design

Natural-gas vehicles use the same basic principles as gasoline-powered vehicles. In other words, the fuel (natural gas in this case) is mixed with air in the cylinder of a four-storke engine and then ignited by a spark plug to move a piston(活塞) up and down. Although there are some differences between natural gas and gasoline in terms of flamability and ignition temperatures NGVs themselves operate on the same fundamental concepts as gasoline-powered vehicles.

Still, some modifications are required

A．Y

B．N

C．NG