Vented hydrogen-air explosions at elevated static activation pressures

The flame behaviors and pressure characteristics of vented hydrogen-air explosions at elevated static activation pressures (Pstat) were investigated using a 20 L spherical vessel. For vented flame, it was found that the maximum flame lengths and widths raised with the increase in venting diameters (Dv) and equivalent ratios (phi) by dominating the concentration of vented unburned gas, while they were insensitive to the change of Pstat. Based on the variation law, non-dimensional formulas for predicting maximum flame length and width were established and the relative error was within 50 %. For internal pressure, the pressure curves were characterized with notably oscillations and an empirical formula coupled with NFPA 68 was proposed with a relative error within 25 %. For external pressure, the mechanism of the external explosion was revealed with the assistance of BOS images. The intensity of external explosion mainly depended on the external flow field intensity and the concentration of the unburned gas. The peaks of external explosion pressure and the pressure recession indices reached their maximum at Dv = 125 mm due to the conflicting effect of the increased Dv.

Automated summary

The flame behaviors and pressure characteristics of vented hydrogen-air explosions at elevated static activation pressures were investigated in this study. It was found that the maximum flame lengths and widths increased with the increase in venting diameters and equivalent ratios by controlling the concentration of vented unburned gas. Non-dimensional formulas were established to predict the maximum flame length and width with a relative error within 50%. The pressure curves exhibited notable oscillations, and an empirical formula was proposed to predict the internal pressure with a relative error within 25%. The mechanism of external explosions was revealed using BOS images, and it was found that the intensity of external explosions depended on the external flow field intensity and the concentration of unburned gas.