Spray impingement and the resulting liquid fuel films are main causes of soot emissions in gasoline direct-injection (GDI) engines. This work presents an experimental investigation of liquid fuel-film formation and evaporation with UV-absorption imaging at a condition representative for engines. One of the 8-hole "Spray G" injectors from the Engine Combustion Network (ECN) was used in a constant-volume vessel, with a transparent plate mounted perpendicular to the injector axis at 30 mm from the nozzle. A fuel surrogate consisting of 30% toluene and 70% iso-octane was injected at 200 bar. The gas and wall temperature were 100°C, and the gas pressure 1 bar. Spatio-temporally resolved measurements of the film thickness were obtained by high-speed imaging of the UV absorption of toluene. For this purpose, the plate that the sprays impinged on was illuminated with an array of UV LEDs at 265 nm, collecting the transmitted light with an intensified CMOS camera. Since vapour and liquid cannot be distinguished spectrally, morphological post-processing was developed to separate them based on spatio-temporal features in their appearance in the image sequences. The images then provide quantitative information on the evolution of the films thickness, mass, and surface area.
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