Mixture formation is fundamental for the development of the combustion process in internal combustion engines, for the energy release, the consumption, and the pollutant formation. Concerning the spark ignition engines, the direct injection technology is being considered as an effective mean to achieve the optimal air-to-fuel ratio distribution at each operating condition, either through charge stratification around the spark plug and stoichiometric mixture under the high power requirements. Due to the highest injection pressures, the impact of a spray on the piston or on the cylinder walls causes the formation of liquid film (wall-film) and secondary atomization of the droplets. The wall-film could have no negligible size, especially where the mixture formation is realized under a wall-guided mode.
The present work aims to report the effects of the ambient pressure and wall temperature on the macroscopic parameters of the spray impact on a wall. The spray-wall interaction was realized inside an optically-accessible quiescent vessel and its development was analyzed by a z-shaped combined schlieren / Mie scattering set-up, using a high-speed C-Mos camera for the image acquisition. The arrangement was capable to acquire alternatively the schlieren and Mie-scattering images in a quasi-simultaneous mode along the same line-of-sight. This methodology allowed complementing the liquid phase with the gas/vapor one resolved in the injection cycle. Isooctane fluid was injected using a Spray G eight-hole injector from the Engine Combustion Network (ECN) circuit. Spatial and temporal evolutions were measured through several image processing steps for both the phases in terms of width slippering and thickness growth. The effects of both the ambient pressure and wall temperature on the width and thickness for the liquid and the vapor phases are discussed.