Burning Characteristics of Liquid Fuels with Suspensions of Energetic Nanoparticles: The Effect of Droplet Size

Abstract

The goal of this study 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 experimental setup was developed to produce a droplet stream with droplet sizes ranging from 100-600 μm. The droplet stream was ignited using a heated coil technique, producing a stable droplet stream flame. Pure ethanol and ethanol with the addition of aluminum nanoparticles at varying concentrations were tested with an initial droplet size of 176 μm. Macroscopic visualization of the flames showed micro-explosions to appear in the flame as the nano aluminum burns and escapes 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 2 wt. % aluminum), the burning rates remained stable, following the D 2 -Law of droplet burning. On the other hand, for higher concentrations, the burning rate reduces as a function of time hence deviating from the D 2 -Law. Tests are being conducted for larger droplets (500-600 μm) at higher concentrations of aluminum. Thin filament pyrometry (TFP) is being used to investigate the temperature distributions within the flame and the effect nanoparticle addition has on the absolute flame temperatures.