Influences of Residence time of Fuel Vapor Transport on Sooting Behavior of Ethanol Droplet Flames in Microgravity

A series of experiments were performed to elucidate the influence of residence time of fuel vapor transport on the sooting behavior of microgravity ethanol droplet flames using the 2.2 sec drop-tower facilities at the NASA Glenn Research Center (GRC). In these experiments, the residence time of fuel vapor transport was adjusted by means of changes in initial droplet diameters (1.6 mm versus 1.9 mm) and oxygen concentrations (ranging from 21 % to 33 % mole fraction in argon atmospheric environments). As the flame temperature is increased, the measured soot volume fraction initially increased and then began to decrease after reaching a maximum value. Experimental results clearly indicate that the residence time can control the sooting behavior for microgravity droplet flames by mediating the competition among the fuel pyrolysis reactions, fragmentation of formed soot precursors, and oxidation of soot precursors and particles which eventually result in an interesting non-monotonic sooting behavior at elevated flame temperatures.