Natural Gas & CNG Fuel Characteristics

Natural gas is normally a gas, not a liquid. A high methane content gives natural gas its high octane rating (120-130) and clean-burning characteristics, allowing high-engine efficiency and low emissions. It is stored by being compressed to 3600 pounds per square inch (psi).  Compressed Natural Gas (CNG) fuel containers are thicker and stronger than gasoline or diesel containers, so they weigh more and take up more space.

To provide adequate driving range, CNG must be stored on board a natural gas vehicle in tanks at high pressure—up to 3,600 psi. A NGV gets about the same fuel economy as a conventional gasoline vehicle on a gasoline gallon equivalent (GGE) basis. A GGE is the amount of alternative fuel that contains the same amount of energy as a gallon of gasoline. A GGE equals about 5.7 lb (2.6 kg) of CNG.

Natural gas has a high ignition temperature, about 1,100 degrees Fahrenheit, compared with about 600 degrees Fahrenheit for gasoline. Natural gas has a very limited range of flammability – it will not burn in concentrations below about 5% or above about 15% when mixed with air. Gasoline and diesel burn at much lower concentrations and ignite at lower temperatures. The high ignition temperature and limited flammability range make accidental ignition or combustion of natural gas less likely.

Source:  NGVAmerica and U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE)