Effect of TPGME Blending on Soot Emissions from JP8 Fuel Droplets Burning with Spherical Symmetry

Abstract

Combustion of stationary fuel droplets of JP8 (a kerosene derivative) mixed with tripropylene glycol mono-methyl ether (TPGME, CH3[CH2CH(CH3)O]3OH)) was examined to understand the influence of oxygenate concentration on particulate emissions and burning process of the fuel blend. The experimental configuration examined was that of spherical symmetry in the droplet/flame configuration, promoted in the experiments reported in this paper by a low gravity environment. Such a state of symmetry for a droplet burning situation corresponds to a one-dimensional transport configuration that is particularly useful for modeling purposes, and for understanding the underlying mechanisms involved in the various features observed. Prominent among these are the fate of soot aggregates formed during the droplet burning process which are trapped between the droplet and flame in a very porous cloud. Experiments are reported for TPGME mixed with JP8 in concentrations of 10% and 20% in volume, which correspond to the industrially relevant oxygenate concentration of between 3.7% and 7.2%. Principle diagnostics are a high-speed 16 mm movie camera, and a high resolution color video camera, to provide both qualitative information on sooting dynamics and quantitative information on droplet mass transport including droplet flame and soot cloud diameters. To isolate the effect of TPGME on sooting tendency, initial droplet diameters (which generally influence sooting) were kept within a narrow range (average of 0.45 mm ± 0.05 mm) to eliminate the impact of the initial diameter in the interpretation of the results. The ambient gas conditions were room temperature air and atmospheric pressure. Results showed that TPGME addition has a significant impact on the sooting dynamics with flames showing significantly less soot formed, especially at 20% concentration in the mixture. TPGME addition reduced the tendency of droplet heating and increased the burning rate. Preferential vaporization behavior was most pronounced at 20% concentration. Sooting propensities are in the approximate order of JP8 > JP8+10% TPGME > JP8+20% TPGME.