Boiling in acoustically levitated nanofuel droplets

Inclusion of metal/metalloid particles in conventional hydrocarbon fuels has unearthed the possibilities of nexgen energetic fuels. Recent research stride on nanofuel (Base Fuel $+$ Nanoparticles) combustion has shown a unique pathway of droplet secondary atomisation, stemming from heterogeneous boiling. Presence of nanoparticles (NPs) aids internal ebullition in nanofuel droplets. Rupture and expulsion of the bubbles generate high-speed ligaments which further undergo tip break-up. In the current work, we report detailed analyses of evaporation and atomisation characteristics of nanofuel droplets in a contactless environment (acoustic levitation) under external radiative heating. We explore the critical parameters for bubble incipience by varying base fuel vapour pressure, initial droplet size, and the input laser power. A time scale analysis considering orthokinetic NP aggregation, evaporation lifetime, and bubble growth rate is presented to elucidate the mechanism of internal boiling. A theoretical non-dimensional time scale ($\tau $*) is devised for calculating the lower limit for droplet size necessary to exhibit internal ebullition. REFERENCE Pandey K., and Basu S. `How boiling happens in nanofuel droplets' Physics of Fluids, 2018, 30, 107103.