Effect of vent area on vented deflagration of hydrogen–methane–air mixtures

Abstract

In this study, experiments on the vented deflagration of hydrogen–methane–air mixtures were performed in a vertical rectangular duct with a vent at its top end. A nondimensional vent coefficient (Kv) was employed to characterize the effects of vent area (Av) on flame evolution and pressure buildup within and outside the duct. The maximum internal overpressure was attained near the duct bottom for a certain Kv. As Kv was increased from 2.2 to 11.9, the maximum internal overpressure near the vent and at the center of the duct increased monotonically; however, a nonmonotonic trend was observed at the duct bottom. Helmholtz oscillations of the internal flame and overpressure were observed in the tests for low Kv, and acoustic oscillations of the internal overpressure with a frequency of ~1200 Hz appeared in all tests. The maximum external overpressure first increased and then decreased with an increase in Kv. The external explosion induced a pressure peak in the duct, and the effect of external explosion on the venting of the internal deflagrations was weakened as Kv ≥ 7.8.