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A major source for soot particle formation in Gasoline-Direct-Injection (GDI) engines are fuel-rich zones near walls as a result of wall wetting during injection. To address this problem, a thorough understanding of the wall film formation and evaporation processes is necessary. The wall temperature before, during and after fuel impingement is an important parameter in this respect, but is not easily measured using conventional methods. In this work, a recently developed laser-based phosphor thermography technique is implemented for investigations of spray-induced surface cooling. This spatially and temporally resolved method can provide surface temperature measurements on the wetted side of the surface without being affected by the fuel-film. Zinc oxide (ZnO) particles, dispersed in a chemical binder, were deposited onto a thin steel plate obtaining a coating thickness of 17 μm after annealing.

To meet future particulate emission limits is quite ambitious for gasoline engines working with direct injection. It was found that there is a relationship between the fuel deposited on the combustion chamber surfaces due to spray impingement and the soot emissions. To understand and avoid the fuel film formation, measurements of the fuel film thickness and mass are important. However, in practical applications fuel films in general are not always problematic as long as they evaporate in time before ignition. Therefore, a systematic investigation of the evaporation duration of fuel film resulting from spray/wall interaction using high-speed visualization was performed. The investigation focused on the influence of engine related operating parameters on the film evaporation duration under the typical homogeneously charged gasoline engines conditions.