Study on the deflagrations of H2/air in a 1-m3 vessel with a hinged aluminum vent panel: Effects of hydrogen concentration and ignition position

The effects of ignition position and hydrogen concentration on the pressure build-up and flame evolution during H₂/air deflagrations were studied in a 1-m³ vessel with hinged aluminum vent panel. Three ignition positions were tested: TI (top ignition), CI (central ignition), and BI (bottom ignition), with hydrogen concentrations ranging from 12 vol% to 27 vol%. Explosion overpressure was simulated using the CFD software FLACS and validated against experimental data. Results revealed that Helmholtz oscillations occurred only for 12–18 vol% H₂/air mixtures at TI. Three overpressure peaks inside the vessel were identified: P₁, P₂, and P_vib, caused by the opening of the aluminum panel, interplay between the external explosion and the venting process, and flame-acoustic oscillations, respectively. Compared to inertia-free venting, the aluminum panel significantly increased P₁ at TI. For CI, the panel enhances the external explosion, but it weakens the explosion at BI. When hydrogen concentration exceeded 18 vol%, the maximum explosion overpressure (P_max) at all ignition positions increased with increasing hydrogen concentration. An external overpressure peak, P_ext, was observed at all ignition positions for hydrogen concentration above 18 vol%. For TI, an additional overpressure peak, P_open, caused by the propagation of the flame wave after the aluminum panel opening, was recorded. The maximum external overpressure (P_e-max) increased with hydrogen concentration. The simulated values of P_max and P_e-max closely matched the experimental data for CI. However, simulations overestimated the experimental results for hydrogen concentration above 18 vol% at TI and BI. Additionally, the vent panel obstructed external flame propagation.