DDT run-up distance for stoichiometric hydrogen-methane-oxygen measured in an orifice plate filled tube

Abstract

Flame acceleration and deflagration-to-detonation transition (DDT) was studied in a 2.88-m, 7.6-cm inner-diameter transparent round tube filled with repeating 50 % blockage-ratio orifice plates. Stoichiometric hydrogen/methane/oxygen, with different hydrogen-to-methane mole ratios, and argon-diluted stoichiometric hydrogen-oxygen mixtures were tested. These mixtures span a range of detonation cell structure regularity. The reactivity of the mixture was controlled by varying the initial pressure, from the DDT critical pressure to a maximum of 40 kPa. Flame velocity was measured from high-speed video. The DDT run-up distance was obtained directly from the video images, and soot foils were used to confirm the DDT location at the critical initial pressure and to measure the detonation cell size at the end of the tube void of obstacles. The DDT run-up distance was shorter for methane containing mixtures at the lowest initial pressure near the DDT limit but was the same for all mixtures at pressures greater than 15 kPa. For each mixture, the DDT run-up distance decreased with the detonation cell size according to an inverse power-law. For a given detonation cell size, the DDT run-up distance decreases with increased methane-fraction. Therefore, for a given orifice diameter, at the DDT limit (where the orifice diameter roughly equals the detonation cell size), the DDT run-up distance for methane-containing mixtures is shorter than for 100 % hydrogen. This, and the fact that a higher initial pressure is required for methane containing mixtures to have the same cell size, needs to be considered when assessing the explosion hazard of hydrogen/methane mixtures.