Compressed natural gas (CNG) is a fuel gas mainly composed of methane (CH4), compressed 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 , usually in cylindrical or spherical shapes. CNG is used in traditional petrol/internal combustion engine vehicles that have been modified, or in vehicles specifically manufactured for CNG use: either alone (dedicated), with a segregated liquid fuel system to extend range (dual fuel), or in conjunction with another fuel (bi-fuel). It can be used in place of petrol (gasoline), diesel fuel, and liquefied petroleum gas (LPG). CNG combustion produces fewer undesirable gases than the aforementioned fuels. In comparison to other fuels, natural gas poses less of a threat in the event of a spill, because it is lighter than air and disperses quickly when released. Biomethane – refined biogas from anaerobic digestion or landfills – can be used. In response to high fuel prices and environmental concerns, CNG has been used in auto rickshaws, pickup trucks, transit and school buses, and trains. The cost and placement of fuel storage containers is the major barrier to wider/quicker adoption of CNG as a fuel. It is also why municipal government, public transportation vehicles were the most visible early adopters of it, as they can more quickly amortize the money invested in the new (and usually cheaper) fuel. In spite of these circumstances, the number of vehicles in the world using CNG has grown steadily (30 percent per year). Now, as a result of the industry's steady growth, the cost of such fuel storage cylinders has been brought down to a much more acceptable level. Especially, for the CNG Type 1 and Type 2 cylinders, many countries are able to make reliable and cost effective cylinders for conversion need. CNG's energy density is the same as liquefied natural gas at 53.6 MJ/kg. Its volumetric energy density, 9 MJ/L, is 42 % of that of LNG (22 MJ/L) because it is not liquefied, and is 25 percent that of diesel fuel.
François Maréchal, Shivom Sharma
Olivier Sauter, Yiming Li, Ambrogio Fasoli, Basil Duval, Jonathan Graves, Duccio Testa, Patrick Blanchard, Alessandro Pau, Federico Alberto Alfredo Felici, Cristian Sommariva, Antoine Pierre Emmanuel Alexis Merle, Haomin Sun, Michele Marin, Henri Weisen, Richard Pitts, Yann Camenen, Jan Horacek, Javier García Hernández, Marco Wischmeier, Nicola Vianello, Mikhail Maslov, Federico Nespoli, Yao Zhou, Davide Galassi, Antonio José Pereira de Figueiredo, Hamish William Patten, Samuel Lanthaler, Emiliano Fable, Francesca Maria Poli, Daniele Brunetti, Anna Teplukhina, Alberto Mariani, Kenji Tanaka, Bernhard Sieglin, Otto Asunta, Gergely Papp, Leonardo Pigatto