Flame characteristics of premixed H2-air mixtures explosion venting in a spherical container through a duct

Pressure release characteristics of premixed hydrogen-air mixtures in an explosion venting device with a duct

Experimental and numerical study on the effect of low vent burst pressure on vented methane-air deflagrations

Visualization of explosion characteristics of methane-air mixtures with different ignition positions and vent areas in a large-scale venting chamber

Experiments were conducted in a 1 m3 vessel with a top vent to investigate the effect of methane concentration and ignition position on pressure buildup and flame behavior. Three pressure peaks (p1, p2, and Pext) and two types of pressure oscillations (Helmholtz and acoustic oscillations) were observed. The rupture of vent cover results in p1 that is insensitive to methane concentration and ignition position. Owing to the interaction between acoustic wave and the flame, p2 forms in the central and top ignition explosions when the methane–air mixture is near–stoichiometric. When the methane–air mixture is centrally ignited, p2 first increases and then decreases with an increase in the methane concentration. The external explosion-induced Pext is observed only in the bottom ignition explosions with an amplitude of several kilopascals. Under the current experimental conditions, flame–acoustic interaction leads to the most serious explosions in central ignition tests. Methane concentration and ignition position have little effect on the frequency of Helmholtz and acoustic oscillations; however, the Helmholtz oscillation lasts longer and first decreases and then increases as the methane concentration increases for top ignition cases. The ignition position significantly affects the Taylor instability of the flame front resulting from the Helmholtz oscillation.

Effect of concentration and ignition position on vented methane–air explosions

This study investigates the effect of the ignition position on vented hydrogen-air deflagration in a 1 m3 vessel and evaluates the performance of the commercial computational fluid dynamics (CFD) code FLACS in simulating the vented explosion of hydrogen-air mixtures. First, the differences in the measured pressure-time histories for various ignition locations are presented, and the mechanisms responsible for the generation of different pressure peaks are explained, along with the flame behavior. Secondly, the CFD software FLACS is assessed against the experimental data. The characteristic phenomena of vented explosion are observed for hydrogen-air mixtures ignited at different ignition positions, such as Helmholtz oscillation for front ignition, the interaction between external explosion and combustion inside the vessel for central ignition, and the wall effect for back-wall ignition. Flame-acoustic interaction are observed in all cases, particularly in those of front ignition and very lean hydrogen-air mixtures. The predicted flame behavior agree well with the experimental data in general while the simulated maximum overpressures are larger than the experimental values by a factor of 1.5–2, which is conservative then would lead to a safe design of explosion panels for instance. Not only the flame development during the deflagration was well-simulated for the different ignition locations, but also the correspondence between the pressure transients and flame behavior was also accurately calculated. The comparison of the predicted results with the experimental data shows the performance of FLACS to model vented mixtures of hydrogen with air ignited in a lab scale vessel. However, the experimental scale is often smaller than that used in practical scenarios, such as hydrogen refueling installations. Thus, future large-scale experiments are necessary to assess the performance of FLACS in practical use.

Effect of ignition position on vented hydrogen–air deflagration in a 1 m3 vessel

The effects of vent area on pressure and flame evolution in a 1 m3 vessel with and without obstacles were investigated. Five pressure peaks of Popen, Pout, Pext, Phel, and Pvib, which correspond to vent activation, flame venting, external explosion, Helmholtz oscillation, and the coupling of acoustic waves and flames, respectively, were observed without obstacles when the vent coefficient Kv ≤ 6.25. However, the pressure peaks of Pext and Pout from the external explosion and flame venting disappeared when K v > 6.25. Moreover, the pressure peaks of Popen and Pvib produced by vent activation and acoustically enhanced combustion become dominant when K v ≥ 12.5. With the installation of obstacles, the pressure peak Pvib induced by acoustically enhanced combustion disappeared. The other four pressure peaks were observed when K v K v ≥ 12.5. Nevertheless, the pressure peak resulting from the obstacles was observed and became dominant at K v ≥ 12.5. It takes less time for the external flame to propagate to the maximum displacement in the tests with obstacles than that without obstacles, and the maximum flame length for the former is smaller than the latter.

Shengchao Rui

Papers

Experimental and numerical study on the effect of low vent burst pressure on vented methane-air deflagrations

Effect of ignition position on vented hydrogen–air deflagration in a 1 m3 vessel

Effect of vent area on the vented methane-air deflagrations in a 1 m3 rectangular vessel with and without obstacles