In a natural-gas-powered vehicle, energy is released by the combustion of methane gas () fuel with oxygen () from the air to form carbon dioxide () and water vapor () in an internal combustion engine. Methane is the cleanest burning hydrocarbon, and many contaminants present in natural gas are removed at the source. Existing gasoline-powered vehicles may be converted to CNG or LNG and can be dedicated (running only on natural gas) or bi-fuel (running on gasoline or natural gas). Diesel engines for heavy trucks and buses can also be converted and can be dedicated with the addition of new heads containing spark ignition systems or can be run on a blend of diesel and natural gas, with the primary fuel being natural gas and a small amount of diesel fuel being used as an ignition source. It is also possible to generate energy in a small gas turbine and couple the gas engine or turbine with a small electric battery to create a hybrid electric motor-driven vehicle.
