How the cylinder initial conditions affect the HCNG refuelling process - A thermodynamic analysis to determine the most effective filling parameters

The hydrogen compressed natural gas (HCNG) blends play a key role in the European Hydrogen Roadmap targets achievement. The HCNG refuelling stations can be built up by upgrading the existing compressed natural gas stations. This work investigates the thermodynamic of HCNG refuelling processes to determine the impact on gas temperature due to the Joule-Thomson effect, heat transfer through the cylinder wall, the kinetic energy conversion in internal energy, and compression contribution during the fast fill-up. Specifically, the vehicle tank initial conditions and the refuelling parameters have been analysed, evaluating how they affect the final refuelling temperatures, filled mass, relative states of charge, and refuelling times. With an average pressure ramp rate of 0.18 MPa/s, at initial cylinder conditions of 10 C and 9 MPa, the 0.065 m3 and 0.15 m3 tanks reach a SOC of 93.83% and 65.32% and final temperature of 82.5 C and 44.5 C, respectively.