Cool-Flame Behaviors of an n-Decane/Ethanol Binary-Fuel Droplet in Microgravity

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Ignition delays and temperatures of cool flame of isolated n-decane/ethanol binary-fuel droplets in hot air were experimentally measured under microgravity and normal gravity by thermocouples. The droplet diameter was about 1 mm. Ambient pressure was atmospheric pressure, and ambi ent temperature was 620 K or 660 K under microgravity and varied between 580 K and 780 K under normal gravity, where only cool flame appears for pure n-decane droplets. Mole fraction of ethanol of the binary-fuel was varied. Near the droplet were placed three hot junctions of K-type thermocouples with a diameter of 25 mm. The droplet center and the three hot junctions were arrayed in a straight line with a constant distance of 2 mm. Both under normal gravity and microgravity, ignition delay decreased with increasing ambient temperature and increased with more addition of ethanol to n-decane. Fuel composition or ambient temperature affected cool-flame temperature very little under microgravity.