Outwardly Opening Hollow-Cone Diesel Spray Characterization under Different Ambient Conditions

The combustion quality in modern diesel engines depends strictly on the quality of the air-fuel mixing and, in turn, from the quality of spray atomization process. So air-fuel mixing is strongly influenced by the injection pressure, geometry of the nozzle duct and the hydraulic characteristics of the injector. In this context, spray concepts alternative to the conventional multi-hole nozzles could be considered as solutions to the extremely high injection pressure increase to assure a higher and faster fuel-air mixing in the piston bowl, with the final target of increasing the fuel efficiency and reducing the engine emissions. The study concerns an experimental depiction of a spray generated through a prototype high-pressure hollow-cone nozzle, under evaporative and non-evaporative conditions, injecting the fuel in a constant-volume combustion vessel controlled in pressure and temperature up to engine-like gas densities in order to measure the spatial and temporal fuel patterns. The spray evolution was characterized by means of two optical techniques, schlieren and Mie scattering. Schlieren images take into account of both liquid and vapor fraction, while the Mie-scattering for the liquid fraction. The images were processed through a customized procedure developed in MATLAB to better outline the contours of the liquid phase and the vapor/atomized zones. Results showed this nozzle configuration appears intrinsically capable of generating a finely atomized spray homogeneously and circumferentially distributed contributing to a better fuel-air mixing level.