Thermodynamic Behavior of Supply Gas and Influence on Vehicle Fuel Fill Line During CNG Fast Fill

The Joule-Thomson effect with a rapid pressure change results in a considerable temperature drop of the gas in the vehicle fuel fill line at the initial stage of fast fill. Since a large volume flows at the beginning of the fast fill, a change in the state of gas in the fuel fill line behaves similar to an adiabatic process, and can be considered to be an isenthalpic expansion. The temperature drop is particularly large when the cylinder is empty or the remaining pressure is low. When the ambient temperature is reduced, the temperature of the fuel fill line becomes lower.

Consequently, it is necessary to consider for lower temperatures in proper specifications for the fuel fill line parts. Providing an orifice on the end of the fuel fill line at the internal solenoid shutoff valve is effective to preventing this temperature drop of gas.