Natural-gas Vehicles
Kermit the Frog once said, "It’s not that easy be in 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 road
and fossil fuels still account for almost 75 percent of the world’s energy
consumption. As gasoline prices 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
form. 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 t0 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
$1500. 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-stroke 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 to make an NGV work efficiently. These changes
are primarily in the fuel storage tank, the engine and the
chassis(底盘). Advantages The biggest advantage of NGVs is that they
reduce environmentally harmful emissions. Natural-gas vehicles can achieve up to
a 93 percent reduction in carbon monoxide emissions, 33 percent reduction in
emissions of various oxides of nitrogen and a 50 percent reduction in reactive
hydrocarbons when compared to gasoline vehicles. NGVs also rate higher in
particulate matter 10 (PM10) emissions. PM10 particles transport and deposit
toxic materials through the air. NGVs that operate in diesel applications can
reduce PM10 emissions by a factor of 10. Natural-gas vehicles also offer
these benefits: NGVs are safer. The fuel storage tanks on an NGV
are thicker and stronger than gasoline or diesel tanks. There has not been an
NGV fuel-tank rupture in more than two years in the United States.
Natural gas costs are lower than gasoline. On average, natural gas costs
one-third less than gasoline at the pump. Natural gas is
convenient and abundant. A well-established pipeline infrastructure exists in
the United States to deliver natural gas to almost every urban area and most
suburban areas. There are more than 1,300 NGV fueling stations in the United
States, and more are being added every day. Natural gas prices
have exhibited significant stability compared to oil prices. Historically,
natural gas prices have exhibited significant price stability compared to the
prices of petroleumbased fuels. This stability makes it easier to plan
accurately for long-term costs. NGVs have lower maintenance
costs. Because natural gas burns so cleanly, it results in less wear and tear on
the engine and extends the time between tune-ups and oil changes.
Disadvantages One of the biggest complaints about NGVs is that
they aren’t as roomy as gasoline cars. This is because NGVs have to give up
precious cargo and trunk space to accommodate the fuel storage cylinders. Not
only that, these cylinders can be expensive to design and build — a contributing
factor to the higher overall costs of a Natural-gas vehicle compared to a
gasoline-powered car. Another drawback is the limited driving
range of NGVs, which is typically about half that of a gasoline-powered vehicle.
For example, Honda’s natural gas Civic, the Civic GX, can go up to 220 miles
without refueling. A typical gasoline-powered Civic can go approximately 350
miles without refueling. If a dedicated NGV ran out of fuel on the road. it
would have to be towed to the owner’s home or to a local natural gas refueling
station, which might be harder to find than a "regular" gas station.
Finally, it should be noted that natural gas, like gasoline, is a fossil
fuel and cannot be considered a renewable resource. While natural gas reserves
in the United States are still considerable, they are not inexhaustible. Some
predict that there are enough natural gas reserves remaining to last another
67.1 years, assuming that the 2003 level of production continues. More and more people are fond of NGVs because they help reduce deaths in car accidents to a great degree.