Hydrogen/air and methane/air flames in axi-symmetric opposed jet burners were investigated experimentally for different flow velocities, burner geometries and fuel dilutions. Above critical strain rate values there is the local extinction of the planar diffusion flame, and the edge flame forms, which propagates and stabilizes further away from the axis of symmetry, assuming a toroidal shape. The ranges of air and fuel flow velocities over which the diffusion or the edge flame are stable were determined. There is a substantial range over which both flames can be stabilized, and the transition between the two flame types exhibits a strong hysteresis. Raman spectroscopy was used for the determination of the spatial distribution of temperature and major species concentrations, while the OH radical distribution was obtained with Planar Laser Induced Fluorescence (LIF). Particle Image Velocimetry (PIV) was employed to characterize the flow fields both in cold and reactive conditions. PLIF平面激光誘導(dǎo)熒光火焰燃燒檢測系統(tǒng)