Abstract
Suitable fluorescence tracers (“dyes”) are needed for the planar measurement of droplet sizes by using a combination of laser-induced fluorescence (LIF) and Mie scattering. Currently, no suitable tracers have been characterized for application in planar droplet sizing in gasoline and kerosene fuels, as well as biofuel blends. One promising tracer is nile red, which belongs to the fluorophore group. For its utilization for droplet size measurements, preliminary characterization of the fluorescence of the respective fuel tracer mixtures are mandatory. For this purpose, the fluorescence and absorption behavior of nile red dissolved in the surrogate fuels Toliso and Jet A-1 as well as in biofuel blends was investigated. The fluorescence signal for nile red that was dissolved in the two base fuels Toliso and Jet A-1 showed a linear behavior as a function of dye concentration. The temperature effect on spectral absorption and emission of nile red was investigated in a specially designed test cell. An ethanol admixture to Toliso led to a spectral shift towards higher wavelengths. The absorption and emission bands were shifted towards lower wavelengths with increasing temperature for all fuels. Both absorption and fluorescence decreased with increasing temperature for all fuels, except for E20, which showed an increased fluorescence signal with increasing temperature. Jet A-1 and its blends with hydroprocessed esters and fatty acids (HEFA) and farnesane did not exhibit explicit variations in spectral absorption or emission, but these blends showed a more distinct temperature dependence compared to the Toliso-ethanol-blends. The effect of photo-dissociation of the LIF signal of the fuel tracer mixtures was studied, and all fuel mixtures besides Toliso showed a more or less distinct decay in the fluorescence signal with time. In summary, all investigated fuel-tracer mixtures are suitable for LIF/Mie ratio droplet sizing in combination with nile red at moderate temperatures and low evaporation cooling rates.
Highlights
Liquid fuel atomization and evaporation behavior controls the subsequent processes of ignition, heat release, and pollutant formation, as well as the efficiency of a combustor
The suitability of nile red as a fluorescence dye for spectroscopic investigations was investigated for the gasoline surrogate fuel Toliso and for Jet A-1 as well as for blends with various biofuels
The fluorescence behavior was studied for nile red dissolved in the two base fuels, Toliso and Jet
Summary
Liquid fuel atomization and evaporation behavior controls the subsequent processes of ignition, heat release, and pollutant formation, as well as the efficiency of a combustor. This process chain is complex and not fully understood, yet the utilization of alternative fuels introduces an even higher degree of complexity to the combustion process. The time for atomization and mixture formation of modern direct injection spark-ignited (DISI) engines is very. An admixture of ethanol to commercial gasoline leads, under certain conditions, to an increase of soot formation within a DISI-engine [1]. An admixture of 20 vol% ethanol (E20) showed an enhanced soot formation in comparison to the base fuel and E40
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