Abstract

After leakage from buried hydrogen-blended natural gas pipelines, gas may seep through the soil into quasi-closed enclosures and form buoyancy-driven non-uniform combustible clouds. The effect of ignition delay on such clouds remains insufficiently understood, particularly regarding the relationship between visible flame development and local thermal response. In this study, 44 soil-seepage combustion experiments were conducted in a 1.5 m × 1.5 m × 1.5 m enclosure. The methane and hydrogen concentrations at three heights, flame evolution, and transient temperatures were measured using gas sensors, high-speed imaging, and thermocouples. The ignition delay ranged from 27 s to 5429 s, with hydrogen blending ratios of 10–30 vol% and ignition positions at the floor, middle, and ceiling levels. The results show that longer ignition delays generally weakened the visible flame luminosity and propagation extent. However, the peak temperature measured by the central thermocouple did not decrease. For the long-delay subset with td > 307 s, the central peak temperature increased with the ignition delay, with R2 = 0.74. Concentration measurements indicated that preferential hydrogen migration and slower methane redistribution continuously reconfigured the local flammability state before ignition. These findings suggest that, in enclosed soil-seepage HBNG scenarios, prolonged ignition delay may weaken visible flame development but does not necessarily reduce local thermal exposure.

IPC Classification

Keywords