Effects of hydrogen concentration on flame propagation and pressure evolution during vented H2/air explosions in a vessel with a hinged panel

This paper investigates the pressure evolution and flame propagation behavior during the vented explosion of H2/air mixtures with hydrogen concentrations(C) ranging from 9 % to 27 %. The experiments were conducted in a 1 m3 vessel equipped with a vent covered by a 4-mm thick hinged aluminum panel. The results reveal three distinct internal pressure peaks during the vented explosion: P1 (the first pressure peak), P2 (the second pressure peak), and P3 (the third pressure peak). When C exceeds 12 %, P2 replaces P3 as the highest-pressure peak within the vessel. As C increases from 9 % to 27 %, P1 becomes less distinguishable in the pressure profiles. The maximum pressure formula proposed by Cubbage and Marshall accurately predicts the maximum explosion overpressure (Pmax) within the vessel. In the external pressure profiles, a maximum external pressure peak (Pext) is observed. As C increases, Pext rises from 4.8 kPa at C = 15 % to 49.9 kPa at C = 27 %. Additionally, as C increases, the maximum external flame speed increases from 170 m/s at C = 21 % to 236 m/s at C = 27 %. When C increases from 18 % to 27 %, the maximum external flame length(Lmax)increases from 1.5 m to 2.0 m. During the inertia-free venting experiments, the fireball, synchronized with the external explosion, assumes a mushroom shape. When hinged panels are used, the fireball becomes progressively flatter at the vent as C decreases.