Preliminary Study of Jet Fuel Droplet Combustion in Microgravity

Abstract

Combustion of stationary JP8 and JP8+100 fuel droplets was studied in a low convection environment. The goal was to promote spherical symmetry in the burning process and to thereby obtain fundamental information on soot structure, burning rate, and evolution of droplet, soot and flame diameters. Spherical droplet flames are an ideal configuration for this purpose because of the one-dimensional droplet burning process it promotes. JP8 and JP8+100 were selected because of their great commercial interest and the fact that little fundamental knowledge is available on their combustion performance, especially for JP8+100. Droplets with initial diameters between 0.44mm to 0.49mm were ignited both in air and in a mixture of 30% oxygen and 70% helium at room temperature to compare results in a nonsooting ambience. Some preliminary experimental results were also obtained at elevated pressure in the helium mixture. High speed 16mm cine photography was the primary diagnostic: color film was used to record the flame structure, and black and white film was used to visualize soot and droplet images. Some data for pure nonane are also included for comparison. At 1atm, significant droplet heating and sooting was found for both JP8 and JP8+100 in air. The ‘+100’ additive influenced only the sooting characteristic as revealed with particularly intense backlighting. As expected, burning in the helium mixture showed much less sooting, and at 3atm in helium significant soot formation returned which indicated a dominant effect of pressure over flame temperature. Droplet burning progressions were nonlinear giving time-dependent burning rates. A scaling relationship was developed that allowed droplet, flame and soot shell diameter data to be presented onto a single curve in a power-law relationship with a scaled time. NOMENCLATURE