In order to design more responsible production processes, "green," environmentally friendly solvents are being considered as alternatives to more complex substances. Achieving greater sustainability across various industrial applications requires deeper knowledge to support the development and optimization of these processes. Specifically, transient two-phase systems, such as sprays, present complex, dynamic phenomena that demand more comprehensive research to understand the mechanisms of atomization, evaporation and mixing. Optical diagnostics enable more detailed analyses of these processes and offer a precise, spatially and temporally resolved quantification of relevant parameters, such as temperature, droplet size and mixture composition. This work presents the advancement and application of fluorescence-based measurement techniques for the quantitative characterization of the liquid phase in sprays and droplets. Especially, first-time applications of micrometric droplet LIF thermometry imaging are presented. The optimization of the two-color technique and additionally reviewed fluorescence approaches aim for a comprehensive characterization of the liquid phase in sprays through planar fluorescence diagnostics. The fluorescent tracers fluorescein disodium and sulforhodamine 101 are admixed to ethanol, water and binary mixtures of each. The temperature-dependent photophysical behavior of the dyes is used for ratiometric two-color laser induced fluorescence thermometry. For a minimization of measurement uncertainties caused by dye influences, extensive investigations of the emission behavior are required. Corresponding calibration measurements are conducted in a temperature-controlled, monodisperse ethanol droplet chain. The enhanced technique is further applied to study heat transfer and evaporation along the heated droplet chain. A microscopic imaging system is used to record the spatially resolved droplet temperatures. Additional investigations in differently tempered atomizing ethanol jets allow for a review of the method’s applicability in polydisperse droplet systems. These studies are conducted with a spectrometer detection setup, providing spectrally resolved information to estimate the influences of stimulated fluorescence emission and reabsorption effects on the recorded spectra. Furthermore, two-photon excitation is utilized to image technical sprays of a commercial injector by laser-induced fluorescence. The microscopic visualization enables the sizing of individual liquid structures even in dense spray regions. As a result, the acquired information provides insight into different breakup mechanisms and the influence of the solvent’s liquid properties on the spray structure.    «

In order to design more responsible production processes, "green," environmentally friendly solvents are being considered as alternatives to more complex substances. Achieving greater sustainability across various industrial applications requires deeper knowledge to support the development and optimization of these processes. Specifically, transient two-phase systems, such as sprays, present complex, dynamic phenomena that demand more comprehensive research to understand the mechanisms of atomiz...    »