Oxygen index effect on the structure of a laminar boundary layer diffusion flame in a reduced gravity environment

Forty-five experimental flames established over a flat plate were analyzed in parabolic flights providing 22 seconds of microgravity conditions to study the influence of the oxygen index the oxidizer flow velocity and the fuel injection velocity on the flame geometry characterized by the stand-off distance flame length and the soot production. A diffusion flame generated from a porous ethylene burner discharging into a parallel oxidizer flow provided a laminar boundary layer. Soot production was tracked using the laser-induced incandescence technique while the spontaneous emission of OH^∗ was used to identify the reaction zone. The stand-off distance exhibited several regimes as the distance from the burner leading edge increases. Experimental results showed that the flame length decreased with the oxygen index and increased with the fuel injection velocity and the oxidizer velocity. The characteristic length scale of soot volume fraction evolved in an opposite manner with the flame length suggesting that the latter is not relevant to define the soot residence time.