Numerical simulation of filling process of natural gas onboard vehicle cylinder

The accurate modeling of the filling compressed natural gas-fuelled vehicle storage cylinders is a complex process, and should be studied deeply. The minimum filling time has positive impact on commercialization of natural gas vehicles. On the other hand, very fast filling may result in unexpected temperature rise, violating the safety standards. This study investigates flow and heat transfer in natural gas vehicle’s onboard cylinder during filling. The cylinder is assumed to be a type III onboard storage cylinder. An axisymmetric computational model for unsteady, compressible turbulent flow has been built. A computational fluid dynamics has been developed for predicting the temperature and pressure change during the fill based on using commercial software Fluent. The natural gas (NG) as working fluid is treated as a real gas. The Redlich–Kwong equation of state has been employed to compute the thermodynamic properties of NG. The computation results have been compared with previously measured values and shows good agreement. The results show that the temperature rise for NG is about 35 K. Most of the heat dissipation from the in-cylinder gas is stored in the cylinder wall during the fill and the heat lost to the ambient is small.