Characteristics of Flame Propagation at Flame Base Region into Premixed Mixture with Concentration Gradient.

Characteristics of a triple flame generated with methane-air mixture are experimentally investigated in various fuel concentration gradients. The OH radical intensity, which obtained by the direct measurement using an interference filter, and the flame position are measured in each case. The flame position shows that the whole flame width between the both premixed flame wings is wider than the flammability limit width of the unburned mixture. The expanding ratio of this flame width rises by increasing the concentration gradient. The result of OH radical intensity indicates that the most active reaction region is at flame base. The heat value supplied in the flammability limit well explains the behavior at the flame base region. It is also clarified that, at the flame base, the diffusion flame is formed away from the stoichiometric premixed flame, and these flames interact each other.