Near field visualization of diesel spray for different nozzle inclination angles in non-vaporizing conditions

Abstract

[EN] Accurate experimental data are often needed to validate computational fluid dynamics models. These models regularly rely on experimental results from single-orifice axially drilled nozzles that do not fully represent real injectors, as the difference in inclination angles creates turbulent conditions at the nozzle outlet, consequences of which on the spray development are not yet fully understood. In this work, near-field visualization was done for two nozzle inclination angles in non-vaporizing conditions. Spray tip penetration, spreading angle, and axis angle fluctuations are reported. Three hypotheses are analyzed: liquid jet breakup mechanism, internal flow development, and cavitation. Experiments were carried out using n-Dodecane, testing a single orifice axially drilled and a three-orifice injector, from the Engine Combustion Network. The spray was observed with a diffused back-illumination technique and a long distance microscope, only visualizing the first 6 mm of spray tip penetration, for three injection pressures and four gas densities at ambient temperature. The multi-orifice injector produced a spray with wider spreading angle, which resulted in smaller penetration values. Additionally, higher spray axis angle fluctuations were observed for the multi-orifice injector, which increased for higher injection pressure and, to a lesser extent, with decreasing chamber density. Further analysis was performed with spreading angle fluctuations measurements, where results showed good agreement with spray axis angle fluctuations trends, implying that complex internal flow structures, and even incipient cavitation, could be present in the multi-orifice injector and be the cause of these spray axis angle fluctuations.