COMPRESSED NATURAL GAS

Compressed Natural Gas (CNG) is a substitute for gasoline (petrol) or diesel fuel. It is considered to be an environmentally "clean" alternative to those fuels. It is made by compressing natural gas (which is mainly composed by methane (CH4), in a percantage range of 70% to 98%). It is stored and distributed in hard containers, at a normal pressure of 200/220 bar, usually in cylindrical or spherical shapes to maintain equal pressure on the walls of the containers.
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Natural gas which is comprised primarily of methane, compressed to a pressure at or above 2,400 pounds per square inch and stored in special high-pressure containers. It is used as a fuel for natural gas powered vehicles. (DOE5)

An alternative fuel for motor vehicles; considered one of the cleanest because of low hydrocarbon emissions and its vapors are relatively non-ozone producing. However, vehicles fueled with CNG do emit a significant quantity of nitrogen oxides.