Natural Gas Hybrid Vehicle

Natural gas is a mixture of hydrocarbons, primarily methane (CH4) but also containing ethane and propane and other gases such as nitrogen, helium, carbon dioxide, hydrogen sulfide, and water vapor.

Natural gas does have a high octane rating and excellent properties for spark-ignited internal combustion engines and is relatively clean burning. It is non-toxic, non-corrosive, and non-carcinogenic and does not present a threat to soil, surface water, or groundwater.

The majority of natural gas available today is extracted from gas and oil wells, while some smaller amounts are derived from supplemental sources such as synthetic gas, landfill gas and other biogas resources, and coal-derived gas.

Currently, it accounts for approximately one quarter of the energy used in the United States. About one third of this is used for residential and commercial uses, one third for industrial uses, and one third to electric power production. Unfortunately, only about one tenth of one percent is currently used for transportation fuel.

Natural gas can be stored onboard a vehicle in either a compressed gaseous (compressed natural gas, CNG) state or a liquefied (liquefied natural gas, LNG) state.

In order to provide an adequate driving range, CNG must be stored onboard a vehicle in tanks at high pressure-up to 3,600 pounds per square inch. A CNG-powered vehicle will get around the same fuel economy as a conventional gasoline vehicle on a gasoline gallon equivalent (GGE) basis.

To provide a greater driving range in a smaller volume, natural gas can be liquefied. To produce LNG, natural gas is purified and condensed into a liquid by cooling to -260°F (-162°C). At atmospheric pressure, LNG takes up only 1/600 of the volume of natural gas in vapor form. Howevr, because LNG must be kept at such cold temperatures, it must be stored in double-wall, vacuum-insulated pressure containers. For this reason, LNG fuel systems are typically only used in heavy-duty vehicles.
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