Characterization of the liquid phase of vaporizing GDI sprays from Schlieren imaging

Isooctane sprays from a multi-hole GDI injector were characterized in a constant volume vessel under different experimental conditions in an inert environment. A macroscale characterization of the vapour and liquid phases of the spray was performed using high-speed Schlieren and Mie-scattering imaging techniques. The segmentation of spray images was carried out through an optimal image processing method. It has been shown that the liquid phase of a vaporizing GDI spray can be reliably distinguished from the vapour phase in a schlieren image. Indeed, the schlieren intensity texture due to vapour density gradients is effectively and selectively filtered, leaving the imprint of the light extinction attributable to the liquid phase of the spray almost unchanged. Therefore, the vapour and liquid phases of the spray were characterized in a truly simultaneous manner. The macroscale parameters of the spray liquid phase obtained from Schlieren imaging were also compared with Mie-scattering measurements acquired quasi-simultaneously. (paper)