Evolution and impingement of an automotive fuel spray investigated with simultaneous Mie/LIF techniques

Abstract

The spatial and temporal evolution of an automotive hollow-cone-type spray was investigated with laser-based imaging diagnostics. Optical conditions of an IC engine were emulated with a test cell that was built from an engine cylinder head to hold a high-pressure gasoline-fuel injector. The use of iso-octane fuel that was doped with 3-pentanone allowed measurements of laser-induced fluorescence (LIF) after excitation with a KrF excimer-laser beam. A versatile optical filter system was designed and built that permits simultaneous measurements of Mie-scattering and laser-induced-fluorescence images using a single laser-light sheet and a single intensified CCD camera. The influence of background signals, caused by reflection of signal light from surfaces, laser-sheet intensity attenuation and signal decrease by scattering, was characterized. Mass distributions showed a distinct pre-spray phase, more so than the Sauter mean diameter (SMD) that was determined from the ratio of LIF to Mie signals using single pulse as well as averaged image pairs. Significant changes in SMD distributions were found after the spray had impinged on a flat surface. The impingement also led to the buildup of a liquid film whose thickness was quantitatively determined from LIF images.