Effect of Variable Cross-section Duct on Flame Propagation Characteristics of Premixed hydrogen/methane/air Combustible Gas

Abstract

ABSTRACT To study the effects of variable cross-section ducts with different configurations on the flame structure, flame propagation speed and overpressure of hydrogen/methane/air premixed gases, a series of experiments were carried out on stoichiometric hydrogen/methane/air mixtures with six hydrogen contents (φ = 0, 10%, 20%, 30%, 40% and 50%). The flame propagates to a distance of 500mm from the ignition end, the sudden change in the cross-section area of the Initially Contracted Cross-Section duct and Centrally Contracted Cross-Section duct will disturb the flame front, the flame only experiences two stages: spherical and finger-shaped. At the sudden change in the cross-section, the smooth flame front folds and forms a turbulent flame. “Tulip” flames can be observed in the Finally Contracted Cross-Section duct and Uniform Cross-Section duct, but the “tulip” flame in the Finally Contracted Cross-Section duct will disappear due to the sudden change of cross-section area of the duct. The flame propagation speed and overpressure increase with increasing hydrogen content. When the flame passes through the sudden change position of the cross-section of the duct, the difference in speed becomes more significant. The shape of the pressure curve varies and pressure oscillation will occurs with the location of a small cross-section tube. Under the same hydrogen content, the overpressure peak value of the duct with Centrally Contracted Cross-Section is the highest, and the overpressure peak value is the lowest when the duct cross-section is uniform.