A spin coating device for the investigation of spray-film interactions under engine relevant conditions

A novel spin coating device for producing homogeneous and stable thin oil films under internal combustion (IC) engine−relevant conditions is presented. A minimum film thickness of 2 µm is achievable, which seems to correspond to the thickness of oil films found on cylinder walls of IC engines. The incorporation of the spin coating device into a high-pressure chamber provides both, adjustable ambient conditions and access for optical measurement techniques. The chamber can be equipped with automotive fuel injectors spraying onto the oil films. Oil film generation is achieved via rotation of a sapphire window as film carrier surface. The resulting film thickness is determined using interferometry. Four different aspects of the evolving film thickness are observed and analyzed: (i) influence of rotational speed, (ii) influence of ambient temperature, (iii) film stability during deceleration and after the end of rotation, and (iv) spatial homogeneity of the film. The results confirm that the main parameter influencing minimum film thickness is rotational speed, as it scales centrifugal forces. As oil viscosity strongly decreases with temperature, ambient temperature has an effect on film thickness, too. The film can be considered homogeneous after end of rotation, which is a prerequisite for well-defined investigations of spray−film interactions.