Effect of Droplet Size on the Burning Characteristics of Liquid Fuels with Suspensions of Energetic Nanoparticles

The objective of this paper is to understand the effect of droplet size (decreasing from a millimeter scale to a micron scale) on the combustion characteristics of nanofluid fuels (liquid fuels with suspensions of energetic nanoparticles). An experiment was developed to produce a droplet stream with droplet sizes ranging from 100-500 μm and spacing between 200-600 μm. The droplet stream was ignited using a heated coil, producing a stable droplet stream flame. Pure ethanol and ethanol with the addition of aluminum nanoparticles at varying concentrations were tested. Macroscopic visualization of the flames showed micro-explosions to appear in the flame as the nano aluminum burns and escape the flame front. Ethanol burned with a blue flame indicating little or no soot formation inside the flame. Residue analysis on the stream showed that the aggregation intensity increases with increasing particle concentration. The aggregate structures are dominated by chain like structures and spherical clusters. The burning rate increased with increasing particle concentration. For low concentrations nanofluids (up to 2wt.% aluminum), the burning rates remained stable, following the D 2 -Law of droplet burning. For higher concentrations, the burning rate reduces as a function of time hence deviating from the D 2 -Law. Increasing particle concentration increased the maximum temperature of stream flame. The nanofluid droplet stream burned at a higher temperature downstream as compared to upstream due to the burning of nanoparticles which burned at a higher temperature then that of ethanol.