Optical Diagnostics of Single Liquid Droplets

Abstract

Most propulsion and energy utilization devices rely on the spraying of liquid-phase fuel or oxidizer, into an energy conversion chamber. The behavior of individual droplets in a spray combustor is a critical part of the combustion process, and currently we can only speculate about several fundamental aspects related to droplet heat-up and evaporation. A series of laser diagnostic techniques has been developed to measure heat and mass transfer associated with individual droplets characteristic of a spray. One such technique provides images of flow patterns along a meridian slice of small droplets using Laser-Induced Fluorescence (LIF), illustrating the presence of internal circulation. Extremely accurate vaporization rate measurements are being performed by using individual droplets as miniature lasers, producing Morphology–Dependant Resonances (MDR). MDR output mode-structure (primarily wavelength) contains information about the laser cavity dimensions and is related to droplet size. Another set of measurements is aimed at studying gas-phase-flow/flame front interactions in a microgravity environment using both planar laser–induced fluorescence and Partical Image Velocimetry, (PIV). By developing new ways of probing individual droplets, an understanding of the fundamental physics governing their behavior may be gained.