Compressed natural gas (CNG) is a fuel that can be used in internal combustion engine vehicles (ICEVs) in place of petrol and diesel. It is made by compressing natural gas which consists mainly of methane (CH4). This means that the combustion of CNG produces fewer gases than petrol and diesel–mainly only carbon dioxide and water vapour. In addition, CNG vehicles emit significantly less carbon dioxide than the ones using petrol or diesel.
All ICEVs can be converted into vehicles that are fueled with CNG and there are also vehicles specially manufactured to use CNG. CNG can be used as the only fuel for the vehicle (dedicated), with a segregated petrol system (dual fuel), or in conjunction with petrol (bi-fuel).
Since CNG is not in liquid form, its energy density is lower than that of petrol. This means that the storage cylinders of CNG have to be rather big to offer good driving range. But since CNG’s price is lower than that of petrol, it is mainly used in big commercial vehicles (trucks) and public transport (buses).