Characterization of Wall Film Formation from Impinging Diesel Fuel Sprays using LIF
Conference contribution, 2010
This paper presents a study of Diesel fuel wall films made in a high-pressure/high-temperature spray rig with the purpose to characterize wall film formation from impinging sprays at different injection conditions and to investigate the applicability of different optical techniques. Sprays are impinging on a quartz surface and the formed fuel film is illuminated by laser light through the quartz and the induced fluorescence is imaged from below. The illumination and detection is either done with a combination of a continuous laser and a high-speed video camera or with a pulsed laser and an intensified CCD camera. The first configuration enables following the development of individual sprays and allows for rapid data collection, whereas the latter provides snapshot images with a higher signal-to-noise ratio. The air density, varied by changing temperature or pressure, has an influence of the velocity of the spray arriving at the surface, but found to have less influence on the velocity of the leading edge of the fuel film propagating on the wall. When the air and wall temperature is raised above 200 C the film propagation velocity and the fuel film area are reduced due to fuel evaporation. When the fuel injection is split into several consecutive pulses, a reduction in film thickness and as well as film area is seen at the end of each pulse, followed by a rapid increase at the start of the following pulse.