Experimental study on the explosion behavior of nonuniform hydrogen/methane/air mixtures in a duct

•Explosion behavior of a nonuniform hydrogen/methane/air mixture is studied.•Increasing α(H2) and td can increase the uniformity of the hydrogen/methane/air mixture.•A triple flame is observed in highly nonuniform hydrogen/methane/air mixtures.•The flame tip velocity and overpressure increase with α(H2) and td. An experimental study is performed on the explosion behavior of a nonuniform hydrogen/methane/air mixture with varying hydrogen volume fractions (α(H2)) in the fuel used and different mixing levels of the fuel/air mixture (characterized by the diffusion time (td) of the hydrogen/methane mixture). Results show that both α(H2) and td considerably impact the explosion behavior of the nonuniform hydrogen/methane/air mixture. Increasing α(H2) and td can increase the uniformity of the hydrogen/methane/air mixture. A triple flame is observed in highly nonuniform mixtures instead of the finger- and tulip-shaped flames seen in more uniform mixtures. The shape of the flame front varies with the degree of fuel/air mixing. As α(H2) and td increase, the propagating flame gradually transitions from a triple flame to a tulip-shaped flame. The flame tip velocity and overpressure increase with α(H2) and td. For a fixed td, the flame tip velocity and overpressure increase slightly as the α(H2) rises from 0 to 40% and rapidly for a large α(H2). These findings suggest that improving the uniformity of hydrogen/methane/air mixtures could increase the severity of explosions for fuels with high hydrogen contents.