Sensitivity of Dropsize Measurements by Phase Doppler Anemometry to Refractive Index Changes in Combusting Fuel Sprays

Summary

In fuel spray combustion fuel droplets experience a wide range of temperatures and hence variations in their densities and refractive indices. In this paper, the sensitivity of Phase Doppler dropsize measurements to fluid refractive index changes is quantified. A light scattering analysis shows that for optical scattering geometries based on a scattering angle of 70 degrees dropsize measurements are practically insensitive to refractive index change. Phase measurements made at other scattering angles will bias the dropsize distribution; in particular, dropsizes at high temperatures will be overestimated if a “cold” refractive index is assumed. By comparing simultaneous phase measurements from two different scattering angles the unknown refractive index of a droplet at high temperature can be quantified and its density and temperature calculated.