Effects of hydrogen ratio on explosion characteristics of hydrogen/methane/air in vented chamber

Abstract

In this study, experiments were performed in a vented cylindrical vessel to investigate the effects of hydrogen ratio (χ) on the vented deflagration of hydrogen/methane/air mixtures with an ignition source located near the vent of the chamber at an initial pressure of 101 kPa and initial temperature of 290 K. Pressure–time histories in the vessel were obtained via a piezoelectric pressure sensor, and flame propagation was recorded using high-speed photography. The experimental results revealed that the flame cellularity appeared earlier as χ increased. The pressure evolution was nearly independent of χ, as it was no higher than 0.15, but depended on χ in the tests with higher values of χ. Acoustic oscillations of the internal overpressure appeared when χ ranged from 0.3 to 0.9, which were closely related to the fine cells formed periodically on the flame surface. The pressure peak due to acoustically enhanced combustion dominated the pressure–time histories, and its amplitude first increased and then decreased as χ increased from 0.6 to 0.9. The overall maximum explosion overpressure (Pmax) did not increase monotonically with an increase in χ, and the highest value was reached at χ = 0.7. Therefore, a non-monotonic trend between Pmax and laminar-burning rate of hydrogen/methane/air mixtures was obtained, which has not been reported in previous studies.