Quantitative vapour concentration measurements in n-dodecane and n-hexadecane sprays

Abstract

Quantitative vapour concentration measurements in evaporating sprays of n-dodecane and n-hexadecane at high pressure and temperature are presented in this paper. These two liquids have been selected as they represent realistic fuels such as diesel and biodiesel, and exhibit significantly different boiling points. The objective of this study is to understand the effect of boiling point on vapour distribution in evaporating sprays. The experiments are performed in a high pressure spray chamber with optical access filled with nitrogen and heated to reach a pressure of 50-bar and temperature of 900 K. Two injection pressures of 1000 and 1500-bar are considered. Planar laser induced fluorescence (PLIF) of an exciplex tracer system consisting of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) and α-methyl naphthalene has been used for vapour concentration measurements. A calibration point relating the TMPD concentration and PLIF signal is obtained by using a fuel vapour jet at a known temperature. Various corrections to the PLIF signal are performed. The vapour mixture fraction (or vapour mass fraction) obtained from the experimental data is compared for the two liquids. It is observed that the mixture fractions for both liquids are very close to each other. An analytical model is used to explain this trend by estimating the variation of mixture fraction along centerline for the two liquids. The model shows the predominance of the density ratio, which is similar for both liquids leading to similarity in the experimental data of mixture fraction. Also, the measurements provide a comprehensive dataset for assessment of CFD simulations of single component evaporating sprays in terms of predicting vapour-air mixing.