Flame Propagation in CH₄/H₂/O₂ Blended Mixtures in Smooth Tubes of Millimeter-Scale

There are few studies of flame propagation and the initiation of detonation for blended mixtures. In this article, an experimental study is conducted to investigate the acceleration of a flame in stoichiometric methane/hydrogen/oxygen (CH₄/H₂/O₂) mixtures in millimeter-scale smooth tubes. In the 1.0- and 1.5-mm tubes, there is no flame acceleration or detonation initiation. The flame propagates at a speed of several m/s. This may occur because of the heat loss on a non-adiabatic wall and the condensation of water vapor. When the molar fraction of CH₄ in a 3.0-mm tube is larger than 0.3, detonation is initiated. The early stage of flame propagation is divided into propagation at a constant velocity, deceleration, and exponential acceleration. An increase in the molar fraction of CH₄ induces a pulsating propagation of a flame.