Experiments on vented H2/CH4/air explosion in a chamber with a hinged panel: Effects of hydrogen volume fraction

Abstract

Explosion venting technology is an effective means of reducing explosive hazards, and hydrogen volume fraction (χ) is one of the important parameters affecting its effectiveness. The vent covers, as a key part of the explosion venting application, consist of two types: inertia-free (e.g., membranes) and inertial (e.g., panels). χ has been extensively studied using inertial-free vent covers, but very limited work has been done using an inertial vent cover. Hence, the effects of χ, ranging from 0 to 1.0, on the vented H₂/CH₄/air explosion were studied in a chamber with a hinged aluminum panel, and the explosion overpressure during venting was simulated by FLACS software. The results show that the flame bubble becomes larger and brighter with increasing χ. However, the time for the flame to travel through the vent ($t_{out}$) and the opening angle of the hinged panel at the time of $t_{out}$ constantly decreases as χ increases from 0 to 1.0. In the tests with χ ≤ 0.6, $p_3$ caused by acoustically enhanced combustion becomes the pressure peak with the highest amplitude in the internal pressure profile, but the pressure peak $p_2$ induced by the external explosion dominates the internal pressure trace for χ > 0.6. In comparison to the H₂/CH₄/air deflagration experiments using an inertialess vent cover, the shape of the external fireball is quite similar for smaller χ in the current study with an inertial vent panel. However, the use of the inertial vent panel results in a more flattened external fireball for larger χ. The highest amplitude of the external pressure peak ($p_{ext}$) and the maximum reduced overpressure ($p_{red}$) increase with increasing χ. Whether the studies are performed with inertial and inertialess vent covers or FLACS simulations, the formation time (Δt) of $p_{ext}$ decreases linearly with increasing χ, but $p_{red}$ increases linearly with $S_l^2$. The explosion overpressure simulated by FLACS is relatively close to the experimental results, and in particular, the simulated $p_{red}$ agrees very well with the experimental value.