Measurement of the compressed natural gas in automative application: a comparitive analysis between mass versus volumetric metering methods

Alternative Gaseous Fuels are not new, but the fuel metering systems have become very sophisticated in order to control the flow of several products, such as Compressed Natural Gas (CNG), Liquefied Natural Gas (LNG), Liquefied Petroleum Gas (LPG), Hydrogen, Methanol and others. Alternative fuels and vehicles are now quite widespread, since they reduce emissions and dependence on foreign oil/energy supplies. In particular, CNG is currently being measured by means of a volumetric method when natural gas is supplied to a petrol pump, while is measured by a mass method when the gas is loaded into the vehicles. These different metering approaches can cause misalignments between the two metering systems, thereby causing arguments and disputes. In this paper, a metrological comparison between the two alternative CNG measurement approaches (volumetric vs. mass flow metering) is carried out. In order to show and to stress the inconsistencies connected to these different measuring methods, the main results of a case study are presented and illustrated.