Fuel distribution of a GDI spray impacting on a heated wall: liquid and vapour phases

The impingement of liquid fuel on combustion chamber walls is one of the major drawback in GDI engines because of its increasing in HC emissions and the effects on the combustion process. In the spray wall-guided configuration, an increasing attention is focused on the film deposit evolution and its role in the soot formation. The surface temperature of the wall is identified as an important parameter affecting the outcome of the fuel after impact. Hence, the necessity of detailed understanding of the spray-wall impingement processes and their effects on the fuel distribution. Aim of this study is a detailed understanding of the interaction between the injected fuel and a flat wall under engine-like conditions, observing both the liquid and the vapour phases as the surface temperature varied (room to 573 K) in a controlled environment. Iso-octane was injected by an eight-hole direct-injection gasoline injector, from the Engine Combustion Net-work (ECN), and investigated at atmospheric backpressure and room gas temperature. Simultaneous Mie scatter-ing and schlieren images were captured in a cycle-resolved mode to perform a visual tracking of the interaction process for both the liquid and the vapour phases. The experiments provided the spatial distribution and the time-resolved evolution of the impact, as well as the post-impingement spray developments under various operating conditions. A customized algorithm, able to catch the contours of the liquid phase and the vapour/atomized zone, was used to extract the diffusion and evaporation parameters that characterized the impingement of the fuel.