Radiative extinction of large n-alkane droplets in oxygen-inert mixtures in microgravity

Experimental observations are presented concerning radiative extinction of large n-alkane droplets in diluent-substituted environments at moderately varied pressures in microgravity onboard the International Space Station. The fuels considered are n-heptane, n-octane, and n-decane with carbon dioxide, helium, and xenon used as inerts, replacing nitrogen as diluents at varying amounts. It is shown that a simple scaling analysis, based on the assumptions that radiative extinction occurs when the flame temperature drops to a critical value and that the radiative heat loss rate is a fraction of the heat-release rate at the flame, is able to correlate the measured droplet diameter at extinction as a function of its initial diameter and of the ambient gas-mixture properties.