Interpretation of Backlit Droplet Images from ISS Droplet Combustion Experiments

Backlit droplet images are evaluated for droplet combustion experiments that have been performed on the International Space Station. The focus of the present analyses is on non-sooting or lightly-sooting droplets. The influences of diffraction, interference, and partial coherence on droplet images are considered via Fourier optics modeling. It is found that light diffraction at the droplet edge can contribute significantly to errors in droplet size measurements. Other error sources include background light variations and partial coherence effects. An image-processing algorithm is proposed to account for the effects of diffraction, partial coherence, and background light variations on measurements of droplet sizes.