Experimental study on the combustion and flame propagation characteristics of CH4/O2/N2 premixed turbulent jets

The combustion and flame propagation characteristics of CH 4 /O 2 /N 2 premixed turbulent jets are investigated experimentally in a constant volume chamber (CVC) under different initial temperature (T ini , 300/400/500/ 600K) and oxygen fractions ( gamma, 0.4/0.6/0.8/1.0) conditions using High-speed camera and schlieren system. Four types of jet tip velocity were found: primary vortex motion at the jet top (M -type 1), secondary vortex motion (Mtype 2), weaker positive and negative feedback between the flame and the flow field (M -type 3), and stronger positive and negative feedback (N -type 4). With the decrease of gamma, the jet acceleration and deceleration mechanism is changed from the top vortex motion mechanism in M -type 1 and M -type 2 to the positive and negative feedback mechanism in M -type 3 and N -type 4. The interaction between the pulsating flow field and the heat release from the pre -chamber transitions to the flow field momentum dissipation. For M -type 1 and M -type 2, there is no significant difference in overpressure dynamics. The N -type 4 exhibits lower peak pressure and pressure rise rates. Moreover, the flame mode was predicted under higher P ini (10 bar <= P ini ) and lower gamma ( gamma <= 0.4) based on empirical equations established by the self -similar analytical model.