Framed in the optimization of the fuel injection in internal combustion engines, laser-induced fluorescence (LIF) spectroscopy and imaging were used to describe the homogeneity and miscibility of fuel, water, and ethanol emulsions. LIF signals from the dye Eosin-Y dissolved in water were employed to track the dispersed phase in the water-fuel-ethanol emulsions. As the dye may undergo physical and chemical changes at different experimental conditions, the effects of the solution's temperature, dye concentration, and photodissociation of fluorescence signals were evaluated. A reduction in the dye fluorescence was observed for a high number of laser pulses due to the dye photodissociation. LIF imaging of the emulsions with and without ethanol addition allowed assessment of its homogeneity and miscibility by calculating the coefficients of variation of multiple LIF images. The observed spatial and temporal LIF-signal fluctuations were associated to the coefficient of variation values as well as to the physical changes of the dispersed phase at different experimental conditions. As numerous applications require the characterization and control of an emulsion's properties, the experimental and data processing methodologies presented by Koegl et al. may be extended to chemical, food, pharmaceutical, and environmental fields.
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