Investigation on fuel wall films using laser-induced fluorescence

Modern gasoline engines use the principle of direct injection. During the warm-up and for early injections the spray droplets contact the piston surface. As a result of the spray-wall interaction a wall film occurs. The liquid film as a fuel rich zone is one important reason of high soot emissions. Therefore it is necessary to carry out investigations on wall film forming and evaporation. It is aimed to reduce the wall film mass. The method of Laser-Induced-Fluorescence is able to quantitatively visualize wall films. Using this technique it is possible to study the effects of spray shape, orientation, operating pressure, injection quantity as well as distance from the wall. The boundary conditions of the test section are close to those of an emission test engine. As a simplified approach the LIF measurements are taken under normal ambient conditions. The applied injector is a common high-pressure six hole nozzle controlled by a magnetic system. Two parameters were varied: the injection pressure and the distance between nozzle and wall. As a result the spatial and time resolved wall film thicknesses were found. The first aim was to design a sensitive setup without using intensifiers. This resulted in a very fine-resolution gray scale and height information. Subsequently the analysis of the measuring system and the calibration were conducted.