How is CNG sold?
CNG is sold and dispensed in kg (kilogram) and not in litres or m. If one considers the above mentioned physical attributes of a gas, it becomes quickly obvious, why a measure for mass (kg) is taken instead of a measure for volume (litre or m). One cubic metre of CNG under 10 bar pressure has just a fraction of the energy value than one cubic metre of CNG under 200 bar pressure. However, one kilogram of CNG has always the same calorific value, no matter whether it has a volume of 500 litres, or just a volume of 60 litres – under 200 bar pressure. 1kg of CNG has a higher energy value than both Petrol and Diesel. Petrol has a energy value of 0.03307 mmbtu / L, Diesel 0.03695 mmbtu / L, and CNG 0.0501 mmbtu / kg, respectively. Depending on the size and the number of the in-built cylinder(s), the mileage of one refilling is about 150 to 300 km.
