Effect of relative humidity on methane explosion characteristics of curved pipes in pipe gallery

To explore the influence of relative humidity on the explosion characteristics of methane-premixed gas in the urban underground pipe corridor. The experiment took a 30° bend pipe as an example, and the relative humidity in the pipe had been set to 50% RH, 70% RH, and 90% RH while changing the methane volume fraction to 7%, 9.5%, and 12% to study its influence on the explosion characteristics. When the methane volume fraction is 9.5%, the relative humidity under the same conditions is set in the straight pipe to compare the parameter changes of flame morphology and explosion pressure. The results show that when the methane in the bend is entirely burned, the flame propagation time is delayed by 32.64% by the influence of relative humidity, the flame is hindered by the wall of the bend, the phenomenon of multiple enhancement occurs, and the flame in the straight pipe decays monotonically with the increase of relative humidity. The relative humidity stabilizes the explosion pressure; the relative humidity of 70% RH in the bend has the best impact on suppressing the explosion pressure, and the relative humidity of 90% RH in the straight pipe dramatically reduces the explosion pressure range. In the bending pipe, the relative humidity inhibited the flame propagation velocity, and the flame propagation velocity at 70% RH and 90% RH decreased by 15.46% and 10.65%, respectively, compared with 50% RH.