Effects of Sealed and Vented Boundary Conditions on Methane Explosion Characteristics in a Reduced-Scale Goaf Model

This study quantitatively investigates the effects of methane concentration and sealed/vented boundary conditions on the transient pressure, temperature, and propagation characteristics of methane–air explosions in a reduced-scale goaf-like enclosure. Experiments were conducted in a 0.5 m3 rectangular chamber at methane concentrations of 8%, 10%, and 12%, with pressure and temperature measured synchronously under sealed and vented boundary conditions. Numerical simulations were further performed to examine explosion-propagation characteristics. The sealed boundary condition produced substantially greater pressure and thermal accumulation within the chamber than the vented condition. The highest measured local pressure and temperature were 0.711 MPa and 552.46 °C, respectively, at 12% methane. The maximum pressure rise rates under the sealed condition were 3.00, 3.00, and 6.25 MPa/s at 8%, 10%, and 12% methane, respectively. Under the vented condition, the pressure and temperature responses exhibited a pronounced non-monotonic dependence on methane concentration, with the strongest measured response among the tested concentrations occurring at 10% methane, close to the stoichiometric composition. At this concentration, the highest measured local pressure and temperature reached 0.341 MPa and 373.05 °C, respectively, while the representative maximum pressure rise rate at P2 reached 5.70 MPa/s. Numerical results further indicate that venting reduces pressure and thermal accumulation within the chamber but can transfer high-temperature, high-velocity explosion products into the connected airway. These findings indicate that methane-explosion hazards in goaf–roadway systems should be evaluated by considering both peak loads and transient energy-transfer characteristics under different boundary conditions.