Naturalgas Vehicles Kermit the Frog once said, 'It's not that easy being 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 gasolinepowered vehicles still rule the road and fossil fuels still ac count for almost 75 percent of the world's energy consumption. As gasoline prices soar and concern over harmful emission mounts, how ever, cars that run on alternate fuel sources will become increasingly important. A naturalgas vehicle, or NGV, is the perfect example of such a carit's fuelefficient, 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 de scribe many different substances that are similar hut 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 tile decay of ancient marine animals. Natural gas also cranes from the decay of ancient organisms, but it naturally takes a gaseous form. instead of a liquid form. Natural gas commonly occurs in association with crude oil. It is derived from both land plants and aquatic(水中的) 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 nonassociated gas, that contain only gas and no oil. Natural gas consists primarily of methane(甲烷) 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, 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 modem well, equipped with diamondstudded 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 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 naturalgas vehicles can fill up their cars at one of 1,300 fueling stations located in the United States. Honda al so offers a personal natural gas pump to people who purchase its naturalgaspowered Civic. The pump uses a home's existing natural gas lines and can be installed for $500 to $1500. Naturalgas Vehicle Design Naturalgas 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 fourstroke engine and then ignited by a spark plug to move a piston up and down. Although there are some differences between natural gas and gasoline in terms of flammability and ignition temperatures, NGVs themselves operate on the same fundamental concepts as gasolinepowered vehicles. Still, some modifications are required to make an NGV work efficiently. These changes are primarily in the fuel storage tank, the engine and t