Development of an imaging technique for measurement of mixture composition and liquid phase temperature in spray processes (MEGA-Spray)

• Applicant: Professor Dr.-Ing. Lars Zigan
• Subject Area: Technical Thermodynamics ; Fluid Mechanics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 570908459

In this project, a measuring technique is developed to simultaneously determine the temperature and composition of droplets in spraying processes. Both quantities may change during evaporation and could affect the subsequent processes. “Green solvents” applied are ethanol and water as well as mixtures thereof, which are relevant for a wide range of energy and process engineering spraying processes. This includes, for example, the spray cooling of electrical components or the production of powdered foodstuffs or pharmaceutical products by spray drying. The injection of (water-containing) ethanol is also relevant for fuel additives in direct-injection gasoline engines or as a solvent for particle synthesis, e.g. in flame spray pyrolysis. The measuring technique is based on laser-induced fluorescence (LIF) and the two dyes fluorescein disodium (FL) and sulforhodamine (SRh) for determining the liquid phase temperature using a two-color LIF method (2C-LIF). The measuring technique is extended by an additional color channel to a 3C-LIF technique in order to determine the mixture composition in two-component systems by means of an additional signal ratio. Spectroscopic point measurements are carried out as well. In addition to the temperature sensitivity of the signals in different mixtures, interfering influences such as pressure, dye concentration and laser energy density are also analysed. The LIF technique is calibrated by using a droplet generator, whereby the mixture composition and the droplet temperature are varied. With these measurements the undesirable influences on the calibration of the 3C-LIF method are studied in detail and corrected. An important goal is the realization of measurements at increased evaporation rates, especially at high droplet temperatures, at which preferential evaporation can also occur. Simultaneous measurements of the droplet temperature and the mixture composition are carried out under technically relevant conditions in the spray. For the macroscopic measurement in the spray, the SLIPI method (Structured Light Illumination Planar Imaging) will be used to minimize interference signals from multiple scattering in denser spray regions. The potential of the extended 3C-LIF technique will be investigated in an optically denser spray at increased ambient pressure and temperatures. In a parameter study under varied boundary conditions, simultaneous measurements of the droplet composition and temperatures are carried out spectroscopically and by imaging on a single shot basis for the first time. Operating points and spray regions are identified, which show preferential evaporation.

• DFG Programme: Research Grants