THERMAL INVESTIGATION OF A GDI MULTI-HOLE SPRAY IMPACT ON A HEATED THIN FOIL

Investigation about operating conditions in modern Gasoline Direct Injection (GDI) engines keeps awake theinterest of car manufacturers in order to be respectful of the strict rules about pollutant emissions imposedby states' laws and regulations. It is well-known the strong influence of surface temperature on droplet-wallinteraction and the resulting liquid film formation. On the other side, it is poor the quantitative knowledgeabout the temperature drop on impact zones and about detection of liquid and gaseous phases after the impacton piston head. The present study focuses on the application of infrared thermography about a multi-hole GDIinjector generated spray impinging on a heated thin foil. Thermal images of the iso-octane fuel impacting onthe heated thin foil are acquired at different delays starting from the impact time. Each acquisition is repeatedin order to obtain phase-averaged images. A parametric study is driven about injection pressure at fixedwall temperature and nozzle-to-wall distance. The temperature difference maps and the temperature dynamicbehavior on a single impact spot are presented. A threshold selection method (Otsu's method) is then appliedon thermal images in order to distinguish the liquid wall film from the cooler dry regions. From temperaturedifference images, the temperature drop on the impact zones is of about 35C starting from the first instantsafter the impact. As a matter, after about 0.5ms, the slipping of the fuel from the center of the impact areaappears.