Modeling gas thermodynamic states and jet flame behaviors of high-pressure gas cylinders in fire scenarios

High-pressure gas cylinders (e.g. hydrogen, compressed natural gas, propane) are widely used for both residential energy supply and vehicular applications. Accurate modeling of high-pressure gas cylinder behavior in fire scenarios is a traditional and still a challenging problem. This study proposes a theoretical framework that thermodynamically characterizes the gas behavior inside the cylinder as an isochoric heating process prior to venting and an isothermal expansion process after venting, and the subsequent gas leakage as an isentropic flow. The model integrates process equations with the van der Waals equation of state to establish a transient leakage formulation, which couples a notional nozzle model and flame dimension models available in the literature. The model predictions of gas pressure and flame length show strong agreement with experimental data from hydrogen cylinders across different volumes (48, 210 L) and nominal working pressures (35, 70 MPa). Compared to expensive case-specific testing, the proposed model provides comprehensive outputs with direct engineering applications, e.g. time-to-explosion prediction at specified burst pressures, release pipe diameter optimization, seamless integration with established radiation models in literature.