Experimental analysis of the injection pressure effect on the near-field structure of liquid fuel sprays

Abstract

Primary atomization and initial spray development are critical in the operation of high-pressure liquid sprays such as the ones used in internal combustion engines. In the current paper, an analysis of the effect of the fuel injection pressure on the near-nozzle spray morphology is performed. For this purpose, a high-magnification diffused backlight imaging technique is set by means of a high-speed light-emitting diode and a long-distance microscope. The technique allows to visualize the first 2 mm of the spray development with a resolution of approximately 250 pixels per millimeter. The images obtained are processed with two different criteria to define the spray contour: one using an optical thickness threshold and a second one based on the intensity derivative on the radial direction. The analysis is focused on three aspects of the spray morphology: the spray angle, its standard deviation, and the standard deviation of the spray contour itself. The results show that the average spray angle is only slightly affected by the injection pressure, being the discharge density the main boundary condition affecting this parameter. Instead, the two standard deviation parameters show a clear increasing trend with the injection pressure, confirming that higher turbulence at the nozzle outlet induces higher variability in the spray shape. Regarding the two contour detection methodologies, similar values are reached in the average spray angle, while some more impact is seen in the spray dispersion, although the same trends are found.