Effects of Natural Gas Compositions on CNG Fast Filling Process for Buffer Storage System

Abstract

The accurate modeling of the fast-fill process occurring in Compressed Natural Gas (CNG) fuelled vehicle storage cylinders is a complex process and should be thoroughly studied. Final in-cylinder conditions should meet appropriate cylinder safety standards. The composition of natural gas plays an important role on its thermodynamic properties and consequently, on the fast-fill process and the final conditions. Here, a theoretical analysis has been developed to study the effects of the natural gas composition on the filling process of an onboard Natural Gas Vehicle (NGV) cylinder. The cylinder is assumed as a lumped system. The analysis is based on laws of thermodynamics and mass balance. Based on AGA8 Equation of State (EOS) and thermodynamics relationships, the required properties of natural gas mixtures have been calculated. The results are presented for an adiabatic system. The results show that the compositions of natural gas have great effects on the filling process and final in-cylinder conditions. Furthermore, the gas with less methane percentage in its composition is more suitable for the filling process. © 2013, IFP Energies nouvelles.