Effect of equivalence ratio on hydrogen-methane-air deflagration in a duct with an open end

In this study, experiments on the vented deflagrations of hydrogen-methane-air mixtures were performed in a duct of length (300 mm) x width (300 mm) x height (1000 mm) duct possessing a 250 mm x 250 mm vent at the top, to investigate the effect of equivalence ratio (phi), in the range of 0.6-1.8, on flame evolution and pressure build-up within and outside the duct at an initial pressure of 101 kPa and an initial temperature of 285 K. phi significantly affects the pressure-time histories and flame propagation in the duct. Helmholtz oscillations of the lower flame front, which resulted in violent Taylor instability, were observed in all the tests. Acoustic oscillations occurred at phi >= 1.0, and three pressure peaks could be distinguished. The pressure peak which dominated the pressure-time histories depended on phi and the distance to the vent. At a given phi, the maximum internal overpressure increased with the distance to the vent. The maximum internal and external overpressures first increased as phi increased from 0.6 to 1.0. Thereafter, they decreased with further increase in phi.