Droplet burning rate enhancement of ethanol with the addition of graphite nanoparticles: Influence of radiation absorption

Abstract

A droplet stream flame was used to measure the burning rate of ethanol droplets with the addition of graphite nanoparticles. Two particle sizes, 50 nm and 100 nm, were used for this study. Results indicate that as particle concentration is increased, the burning rate of the resulting nanofluid droplet also increases. The maximum enhancement of 62% was observed with the addition of 3 wt.% 50 nm graphite nanoparticles. To understand the burning-rate-enhancement phenomenon, a model was developed to estimate the radiation absorptivity by the hybrid droplet from the stream flame. The computational models determine the ratio of radiation retention by the entire depth of the fluid (volumetric absorptivity) using optical properties of both the particles and the fluid along with the penetration of radiation within the nanofluid using the well-known Monte Carlo algorithm that incorporates the aforementioned calculated optical properties of the nanofluid. Results indicate that radiation absorption by the hybrid droplet does play a role in the enhancement of burning rate. More importantly, the absorption is not uniform within the hybrid droplet. It is localized in the region near the droplet surface, promoting boiling at the droplet surface. This mechanism is believed to be responsible for the observed increased burning rate.