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The injection of fuel in a combustion engine cylinder is a highly transient and very complex process which dictates the performance and emissions of engines. Increasing the injection pressure or injecting fuel during late compression stroke tends to increase the combustion efficiency and decrease emissions. However, excessive fuel impingement on piston top and cylinder walls could become major negative issues resulting in very inhomogeneous mixture formation, incomplete combustion, considerable cycle-to-cycle variation, and increased fuel film formation. It is generally assumed that the shape of the piston top has a profound impact on the behaviour on spray impingement, spray propagation, fuel evaporation as well as the cycle-to-cycle variation. This work investigates the spray impingement on surface with various geometrical configurations to develop a deeper understanding of the macroscopic spray behaviour. High-speed Mie-scattering visualisations of spray impact on surfaces in a constant volume chamber are conducted. A parametric analysis with three surface geometries of stepped configurations with slope of 30°, 60°, and 90° is carried out. Probability Presence Imagines are created to evaluate the cycle-to-cycle variations and their effects when the spray impinges on the surface. It reveals that the surface geometry has an immense effect on the spray propagation and, therefore, on the evaporation process. On one hand, the geometry can stretch the spray and improve the spreading of the fuel, indicating an enhanced evaporation. On the other hand, the geometry can also constrict the propagation and thus delay the evaporation. Additionally, by focussing on the cycle-to-cycle variation, significant differences in the impingement process and propagation behaviour are elucidated. For instance, the spray propagation in different cycles develop different film thicknesses and vortex behaviour. Results imply that the impinging geometry could either amplify or weaken a vortex behaviour. This work should establish a link between the surface geometry and the spray behaviour both qualitatively and quantitatively. In addition, the influence of the geometry on the cycle-to-cycle variation will be investigated towards to possibility if the impinging geometry is feasible to dampen the effect of cycle-to-cycle variation while enhancing the evaporation process.
