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.
Worldwide, there were 14.8 million natural gas vehicles by 2011, led by Iran with 2.86 million, Pakistan (2.85 million), Argentina (2.07 million), Brazil (1.7 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.
& 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.
Any existing gasoline vehicle can be converted to a bi-fuel (gasoline/CNG) vehicle. Authorized shops can do the retrofitting, this involves installing a CNG cylinder in the trunk, installing the plumbing, installing a CNG injection system and the electronics.
1. Due to the absence of any lead or benzene content in CNG, the lead fouling of spark plugs is eliminated.
& 2. CNG-powered vehicles have lower maintenance costs when compared with other fossil fuel-powered vehicles.
& 3. CNG fuel systems are sealed, which prevents any spill or evaporation losses.
& 4. Increased life of lubricating oils, as CNG does not contaminate and dilute the crankcase oil.
& 5. CNG mixes easily and evenly in air being a gaseous fuel.
& 6. CNG is less likely to auto-ignite on hot surfaces, since it has a high auto-ignition temperature (540 °C) and a narrow range (5%-15%) of flammability.
& 7. Less pollution and more efficiency: CNG emits significantly less pollutants such as carbon dioxide (CO2), unburned hydrocarbons (UHC), carbon monoxide (CO), nitrogen oxides (NOx), sulfur oxides (SOx) and particulate matter (PM), compared to petrol.