Scale effects on premixed flame propagation of hydrogen/methane deflagration

• An experimental study of scale effects on hydrogen/methane deflagration of premixed flame in venting ducts is presented.
• The “tulip” flame disappeared with increasing cross sectional area and gradually appears with increasing duct length.
• The maximum overpressure decreases with cross sectional area and increases with the length of the duct.

An experimental study of scale effects on hydrogen/methane deflagration of premixed flame in venting ducts is presented. The experiments focused on the effect of scale on flame structure, premixed flame propagation speed and overpressure during hydrogen/methane deflagration. Six ducts with different cross-sections and lengths were used in the experiments. Tests were performed for stoichiometric hydrogen/methane mixtures with five hydrogen fractions (hydrogen fraction from 0 to 100%) under ambient conditions. In the experiment, the “tulip” flame disappeared with increasing cross sectional area and hydrogen fraction. Meanwhile, the tulip flame gradually appears and a more pronounced “tulip” flame is observed with increasing duct length. The effect of cross sectional area coupled with duct length on flame propagation can be attributed to the influence of aspect ratio, while the “tulip” flame formation is only found when the aspect ratio > 6.7. In the experiments, the maximum flame speed has the similar trend with laminar flame speed regardless of whether there was “tulip” flame formation and the maximum flame propagation speed occurs with an aspect ratio of 10. The maximum overpressure decreases with cross sectional area and increases with the length of the duct. The time corresponding to maximum overpressure, tmax decreases with hydrogen addition. Meanwhile, tmax increases with cross sectional area and length of duct.