Evaluation of Free-Floating Droplet Acceleration in ISS Droplet Combustion Experiments

Abstract

Trajectories of free-floating droplets burned in experiments on the International Space Station (ISS) are evaluated from digital images. n-Heptane droplets are observed to move in irregular paths after cool flame extinction with acceleration levels of tens or hundreds of μg and frequencies of 0.2 - 0.3 Hz. Flame oscillations for burning methanol and n-heptane droplets can affect droplet acceleration components. During flame oscillation, droplets exhibit oscillatory acceleration patterns with characteristic frequencies of 0.2 - 0.3 Hz and accelerations of the order of 50 μg. The droplet acceleration magnitudes are significantly larger than measured ISS acceleration levels (g-jitter). It is concluded that motions of free droplets are initially a result of the deployment and ignition processes, while motions later in droplet lifetimes are a result of interactions between the droplets and the gas phase including influences of thermal and solutal Marangoni stresses at the liquid-gas interface.