EFFECT OF PARTICLE LOADING ON THE BURNING CHARACTERISTICS OF BORON-LADEN GEL FUEL DROPLET

Droplet combustion of pure and boron-loaded gel fuels is studied to understand the combustion behavior of gel fuel under atmospheric conditions. Here, Jet A-1 is taken as a base fuel, Thixatrol ST as gellant, and boron as energetic particles. Four kinds of gel fuels are taken for this study with varying boron loadings of 0%, 10%, 20%, and 30% (by weight). Before combustion studies, the rheological properties of all gel fuels were determined. The results show a linear variation of viscosity with an increasing shear rate and with increasing boron content. Combustion characteristics of all these fuels were studied and analyzed. The droplet combustion process was captured using a time-resolved high-speed imaging system. The evolution of droplet profile shows that droplet regresses smoothly for pure gel (PG) sample (0% boron), whereas for the GB10 and GB20 cases with 10% and 20% boron, respectively, the droplet regresses with puffing, disruption, and is followed by micro-explosions. For the GB30 case with 30% boron, the phenomena of micro-explosion occur immediately after the ignition of the droplet. Flame standoff distance decreases with the higher boron-loaded gel fuel. Analysis of secondary droplets explains that: (1) puffing induces a smaller diameter, while micro-explosion ejects daughter droplets of larger diameter. (2) Average secondary flame length increases with the increase of boron loading. As a result, the boron component in gel fuel appears to have a good impact on the whole combustion process. Scanning electron microscopy (SEM) image shows numerous micropores (blow holes) on particle surface in case of GB30 sample while no such pores were present on other counterparts. The micrograph also reveals eroded, flaky, and ashy-like structures in the residue of the GB30 case.