Effect of Nitrogen-Modulated Laminar Burning Velocity on Duct-Vented Hydrogen-Air Explosions

Abstract

To investigate the combined effect of venting and dilution on flame behavior and pressure evolution, nitrogen gas was used to modulate the laminar burning velocity (LBV) of stoichiometric hydrogen/air mixtures to explore the combined effect of venting and dilution on flame dynamics. The results reveal that the coupling of the relief duct and nitrogen dilution affects the flame dynamics, e.g., at LBV = 114 cm/s, the flame becomes planar at the enclosure end. The bulges appear at the enclosure axis, which disappears with the decrease in LBV. Decreasing LBV extends the time interval from ignition to the moment of flame front entry into the vent orifice, while the second peak pressure in the enclosure increases with a shortening time interval. There is a notable reduction in both the duration and magnitude of the negative spike in the pressure difference at the lower LBVs. The original equation is modified to improve the exponential prediction between the maximum pressures in the relief duct and the flame velocity at the end of the enclosure to achieve a greater degree of applicability. At lower LBVs, the interaction between the maximum pressure in the relief duct and the maximum pressure in the enclosure is weak, and the linear dependence is not appropriate for the current hydrogen explosion. Therefore, the correlation is probably variable for different fuel types.

Keywords: Hydrogen explosion, N2 dilution, Secondary explosion, Duct-vented explosion