Experimental Observations On The Geometry And Stability Of A Laminar Diffusion Flame In Micro-gravity

An experimental study is conducted on a laminar diffusion flame established over a 50 mm x 50 mm x 10 mm slab of PMMA subject to a forced oxidizer flow parallel to the surface. The parameters varied are the oxygen concentration, the forced flow velociry and the length of pyrolyzing fuel. Experiments are conducted in micro-gravity to simulate the conditions on board spacecraft and to better approximate the assumptions of classical theoretical developments. The experimental results showed a low oxidizer velocity stability limit linked to a minimum fuel supply to the flame and related to a decrease in the heat feedback from the flame to the fuel surface. The importance of convective transfer of fuel to the flame is underlined and is evidenced by soot glowing (yellow flames) as opposed to blue flames where diffusion of fuel IS dominant. Soot particles are convected towards the flame. A qualitative correspondence of blue flames with theory is observed and significant discrepancies are evidenced as the in~portance of convection increases and the flames become yellow.