COMPRESSED NATURAL GAS
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Compressed natural gas (CNG) is a fossil fuel substitute for gasoline (petrol), diesel, or propane/LPG. Although its combustion does produce greenhouse gases, it is a more environmentally clean alternative to those fuels, and it is much safer than other fuels in the event of a spill (natural gas is lighter than air, and disperses quickly when released). CNG may also be mixed with biogas, produced from landfills or wastewater, which doesn't increase the concentration of carbon in the atmosphere.
CNG is made by compressing natural gas (which is mainly composed of methane [CH4]), to less than 1% of the volume it occupies at standard atmospheric pressure. It is stored and distributed in hard containers at a pressure of 200–248 bar (2900–3600 psi), usually in cylindrical or spherical shapes.
CNG is used in traditional gasoline internal combustion engine cars that have been converted into bi-fuel vehicles (gasoline/CNG). Natural gas vehicles are increasingly used in the Asia-Pacific region, Latin America, Europe, and America due to rising gasoline prices. In response to high fuel prices and environmental concerns, CNG is starting to be used also in tuk-tuks and pickup trucks, transit and school buses, and trains.
Worldwide, there were 12.6 million natural gas vehicles by 2010, up 11.6% over the previous year, led by Pakistan with 2.74 million, Iran (1.95 million), Argentina (1.9 million), Brazil (1.6 million), and India (1.1 million).with the Asia-Pacific region leading with 5.7 million NGVs, followed by Latin America with almost 4 million vehicles.
CNG cars available in Europe are bi-fuel vehicles burning one fuel at a time. Their engine is a standard gasoline internal combustion engine (ICE). This means that they can indifferently run on either gasoline from a gasoline tank or CNG from a separate cylinder in the trunk. The driver can select what fuel to burn by simply flipping a switch on the dashboard.
Several manufacturers (Fiat, Opel (General Motors), Peugeot, Volkswagen, Toyota, Honda and others) sell bi-fuel cars. In 2006, Fiat introduced the Siena Tetrafuel in the Brazilian market, equipped with a 1.4L FIRE engine that runs on E100, E25 (Standard Brazilian Gasoline), Gasoline and CNG.
CNG locomotives are operated by several railroads. The Napa Valley Wine Train successfully retrofit a diesel locomotive to run on compressed natural gas before 2002. This converted locomotive was upgraded to utilize a computer controlled fuel injection system in May 2008, and is now the Napa Valley Wine Train's primary locomotive.Ferrocarril Central Andino in Peru, has run a CNG Locomotive on a freight line since 2005 CNG locomotives are usually diesel locomotives that have been converted to use compressed natural gas generators instead of diesel generators to generate the electricity that drives the motors of the train.
CNG compared to LNG
CNG is often confused with liquefied natural gas (LNG). While both are stored forms of natural gas, the key difference is that CNG is gas that is stored (as a gas) at high pressure, while LNG is in uncompressed liquid form. CNG has a lower cost of production and storage compared to LNG as it does not require an expensive cooling process and cryogenic tanks. CNG requires a much larger volume to store the same mass of gasoline or petrol and the use of very high pressures (3000 to 4000 psi, or 205 to 275 bar). As a consequence of this, LNG is often used for transporting natural gas over large distances, in ships, trains or pipelines, and the gas is then converted into CNG before distribution to the end user.