Effects of Hydrogen Concentration and Flexible-Rigid Obstacles on the Explosion Characteristics of Hydrogen-Enriched Natural Gas

This study examines the effects of hydrogen concentrations (10%, 30%) and rigid obstacle blockage ratio (BR = 0.2, 0.4, 0.6) on explosion characteristics, using an unobstructed case as control. Hybrid flexible–rigid obstacles initially suppress flame propagation but then promote turbulence. Darrieus–Landau instability, flame speed, and explosion pressure increase with rigid BR, enhancing flame wrinkling and vortex dynamics. Instantaneous flame velocity 40 cm from ignition decreases with higher rigid BR but increases with higher hydrogen concentration. Increasing hydrogen fraction alleviates obstacle-induced suppression and shortens flame propagation time. Both the rigid BR and hydrogen concentration amplify peak overpressure and its rise rate. Peak pressure is higher downstream than upstream, while the pressure rise rate shows the opposite trend. At 30% hydrogen and rigid BR = 0.6, downstream peak pressure reaches 267.57 kPa, exceeding the upstream value, while the maximum pressure rise rate occurs upstream—17.63 multiple that of the control. Hydrogen accelerates chain reactions via free radical generation, and obstacles create a positive feedback loop by intensifying turbulence. The overpressure occurrence frequency, derived from a normal distribution function, decreases monotonically with increasing peak pressure both upstream and downstream.