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Feasibility Demonstration of Exciplex Fluorescence Measurements in Evaporating Laminar Sprays of Diesel Fuel
Final rept. 14 May 2008-15 May 2011
YALE UNIV NEW HAVEN CT DEPT OF MECHANICAL ENGINEERING
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A six-month seed project was funded to investigate the feasibility of applying quantitatively laser diagnostic techniques to jet fuel surrogates in well controlled sprays. A significant novelty with respect to previous work is the use of an electrospray to generate initially monodisperse droplet size distributions whose evaporation would be monitored in a preheated inert stream under laminar conditions. The fuel mixture consists of hexadecane C16H34, 89.7 wt., naphthalene C10H8, wt.9, TMPD C6H8N2, N,N,N,N-Tetramethyl-1,4-phenylendiamin, 1.0 wt., and an electrical conductivity enhancer Stadis 450. Such a mixture, although not a typical jet fuel surrogate, was chosen because it is widely used in the spray laser spectroscopy literature to distinguish the liquid phase from the vapor one. Vapor fluorescence centered at 400 nm is calibrated using a heated laminar conflow vapor jet diluted with nitrogen, and is found to be proportional to the vapor mole fraction up to 500 ppm. Vapor fluorescence is found to increase with temperature up to 538 K and then declines. Fluorescence from the liquid phase, i.e. the exciplex NaphthaleneTMPD, is imaged at different fuel flow rates and ambient temperature. These measurements are correlated with complementary ones using a Phase Doppler Particle Analyzer to determine droplet size, velocity, number density and, ultimately, droplet evaporation rate along the spray axis. Additional complementary measurements using sampling of the fuel vapor and off-line gas chromatographmass spectrometry analysis to assess its composition are planned to have as well characterized a description of the spray environment and assess conclusively the potential of the exciplex approach for more challenging turbulent spray systems.
APPROVED FOR PUBLIC RELEASE