Combustion of Two-Component Miscible Droplets in Reduced Gravity

This research focuses on reduced-gravity combustion of binary miscible droplets initially in the mm size range or larger. Combustion experiments were performed using the NASA Lewis 2.2 sec Drop Tower, as well as the Glovebox Facility during a 1995 flight of the Space Shuttle. This paper will focus on work performed over the previous two years. A large number of experiments was performed using the NASA Lewis 2.2 sec drop tower. Mixtures of alkanes and/or alcohols were studied. The fuel components were selected to have significantly different volatilities. Initial oxygen mole fractions from about 0.15 - 0.5 and initial pressures from 0.3 - 3 atm were employed. Different inerts were used (He, CO2, Ar, N2) to change burning rates and sooting behaviors. A major effort has been the analysis of results from these experiments. More recently, particle seeding was employed to allow visualization of flowfields inside droplets in microgravity. In some of these experiments, line-of-sight measurements of average soot volume fractions were made, and thermocouples were used to measure gas temperatures. All experiments (ground and Glovebox) were conducted to gain information on the following: transient droplet diameters (including three staged combustion behaviors and microexplosion); transient flame behaviors (sudden flame contraction, luminosity, extinction); droplet internal flowfields (i.e., whether spherical symmetry was closely approached); behaviors of observable soot particles; transient variations in line of sight soot volume fraction measurements; flame temperatures.