Journal of Safety and Environment

To investigate explosion safety issues associated with localized combustible gas clouds propagating in confined and elongated spaces， a pipeline explosion experimental system capable of generating localized premixed gas clouds was developed. The effects of methane concentration and the volume of localized premixed gas clouds on methane explosion propagation characteristics were systematically studied. High-speed imaging and pressure sensors were employed to measure and analyze key parameters， including flame morphology evolution， flame propagation dynamics， explosion overpressure， and the overpressure rise rate. The results indicate that the volume of the premixed gas cloud has a significant influence on explosion propagation characteristics. As the premixed cloud volume increased from one pipe section to two sections， the flame luminosity was markedly enhanced and the flame propagation velocity increased significantly. The maximum average flame propagation velocity reached 205.88 m/s for the two-section condition， which is substantially higher than the 154.18 m/s observed for the one-section condition. Methane concentration also plays a critical role in both flame propagation dynamics and explosion pressure characteristics. The flame propagation velocity， peak overpressure， and maximum overpressure rise rate all reached their maximum values at the stoichiometric concentration of 9.5%. When the mixture deviated from the stoichiometric condition， the combustion intensity weakened， leading to reductions in both flame propagation velocity and explosion overpressure. For the same deviation from the stoichiometric concentration， the peak overpressure and its rise rate under fuel-rich conditions were significantly higher than those under fuel-lean conditions. In addition， the axial evolution of explosion overpressure in the pipeline exhibited a characteristic pattern: slight initial oscillatory growth， rapid increase， sharp decay， and a slight rebound near the pipe end. The maximum overpressure occurred at 3.75 m， where the superposition of reflected shock waves and their coupling with the combustion wave were most pronounced. These findings provide useful insights for hazard assessment of localized gas cloud explosions and the design of explosion protection strategies in confined spaces.