CNG : An Introduction

Natural gas is made up primarily of methane with trace amounts of other gases. It occurs naturally underground and is extracted through gas wells or in conjunction with crude oil production. For storage purposes it can be stored as compressed natural gas (CNG) or liquid natural gas (LNG).

Vehicles running on CNG may have reduced range as compared to similar gasoline model vehicles. This is a limitation of the fuel storage tanks rather than a limitation of the fuel. For example a dedicated CNG Honda Civic GX has an eight-gallon tank and a gasoline powered Civic has an eleven-gallon tank. Bi-fuel vehicles have a longer range because they have two fuel tanks and can run on gasoline or diesel in addition to CNG. Because methane does not have to vaporize before being burned with oxygen, natural gas can burn cleaner, especially at colder temperatures than gasoline or diesel. LNG is kept at very low temperatures to increase storage capability and therefore provides longer ranges than CNG. Vehicles operating on CNG and LNG have a longer engine life and require less frequent oil change intervals.

Burning natural gas results in lower emissions of sulfur dioxide and particulate matter as well as 20% less carbon dioxide than gasoline or diesel. It is one of the cleanest burning fuels. Natural gas is non-toxic, non-corrosive, less combustible than most other fuels, and has few associated health risks. CNG is stored under high pressures. The range of flammability and combustion is much narrower with CNG, making it safer than gasoline. The flashpoint for gasoline is 250 degrees whereas the flashpoint for natural gas is 1100 degrees. Natural gas is lighter than air and will dissipate if leaked whereas gasoline will sink and puddle. Dedicated CNGs produce little or no evaporative emissions during their fueling and use. In gasoline vehicles, evaporative and fueling emissions account for at least 50% of a vehicle’s total hydrocarbon emissions.

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