Duct-vented explosion of stoichiometric hydrogen/methane/air mixtures at various hydrogen ratios

In this study, the effects of hydrogen ratio (x) on the vented deflagration of stoichiometric hydrogen/methane/air mixtures were investigated in a cylindrical vessel connected with a relief duct at an initial pressure of 100 kPa and an initial temperature of 290 K. Flame behavior and pressure evolution in the vessel, the duct and the free field outside the vented configuration were clarified by means of pressure measurement synchronized with high-speed photography. Experimental results revealed that the secondary explosion in the relief duct significantly affected the venting process because it created a negative pressure gradient and consequently a reverse flow regardless of x. The pressure peak in the relief duct resulting from the secondary explosion was higher than the maximum explosion overpressure in the vessel when x > 0.8, and a shock wave in the relief duct was visualized in these tests. Various pressure peaks in the pressure-time histories in the vessel owing to vent failure, reverse flow, and acoustically enhanced combustion could be distinguished when x <= 0.8, and the one which was dominant depended on x. Only one pressure peak formed when x > 0.8. The average maximum explosion overpressure in the vessel increased monotonically from 26 kPa to 289 kPa as x increased from 0 to 1.0. The maximum rate of pressure rise in the vessel approximated that in the duct when x <= 0.45, but the former was much lower than the latter in the tests with higher xs. The average maximum overpressure outside the vented configuration, owing to external explosion, increased from several kPa to 62 kPa with x increasing from in 0 to 1.0, and a shock wave downstream of the relief duct formed when x > 0.8.