Acoustically-Driven Combustion Dynamics and Extinction in Burning Nanofuel Droplets*

This study investigates combustion of liquid fuel droplets containing energetic aluminum nanoparticles (nAl) in an acoustic waveguide, extending prior studies on ethanol to examine the nature of extinction as well as the impact of nAl on sooting hydrocarbon liquids such as dodecane and Fischer–Tropsch (FT) synthetic fuel.  The addition of nAl to ethanol alters flame dynamics close to extinction, with attendant effects on estimated extinction strain rates.  For sooting hydrocarbons, surfactant (Span80) is required to maintain a uniform dispersion of nanoparticles, and this in and of itself causes increases in the burning rate constant (K) with increasing surfactant concentration.  Both Span80 and nAl concentrations impact droplet combustion behavior, with and without the application of acoustic excitation. As with nAl additives to ethanol, acoustically-perturbed, sooting droplets can burn for much longer periods of time than in the absence of particle additives, demonstrating continuous oscillatory combustion as enhanced particle dispersion takes place within the liquid.  These studies are relevant to other acoustically-coupled reactive systems, such as gaseous jet flames, also currently under exploration.