Vehicles running on compressed natural gas (CNG) have been gaining in popularity in Europe in recent years, largely because of the reduced operating costs. Natural gas is much less expensive in Europe than either gasoline or diesel fuel. It also has an advantage over the liquid fuels in that it burns cleaner with almost no particulates.

One downside to CNG is that, like ethanol, it has a lower energy content than gas or diesel which tends to hamper the range and increase consumption. American owners of the Honda Civic GX are familiar with the range limitations. Also like ethanol, it has a higher octane rating; CNG is rated at 130.

Manufacturers are now designing and tuning engines specifically to optimize them for CNG use. Many of the newer CNG engines, like those from Volkswagen, are turbocharged. By running higher boost levels and using direct injection, the engines can get more of the energy out of the fuel, allowing down-sizing, better efficiency and reduced CO2 emissions. In addition, European-market CNG vehicles are typically bi-fuel, retaining their gasoline fuel systems. This allows drivers to keep going even when there isn't a CNG filling station nearby.

[Source: Ward's Auto World]  [ Source: green.autoblog.com ]