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

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 ( K v ) was employed to characterize the effects of vent area ( A v ) on flame evolution and pressure buildup within and outside the duct. The maximum internal overpressure was attained near the duct bottom for a certain K v . As K v 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 K v , 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 K v . 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 K v ≥ 7.8. • Effect of vent coefficient ( K v ) on vented hythane–air deflagration was studied. • The overall maximum internal overpressure increased non-monotonically with K v . • Maximum external overpressure first increased and then decreased as K v increased. • Helmholtz oscillations occurred in the tests for low K v .