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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. [ABSTRACT FROM AUTHOR]

This article introduces an innovative method for the segmentation of Mie-scattering and schlieren images of GDI sprays. The contours of the liquid phase are obtained by segmenting the scattering images of the spray by means of optimal filtering of the image, relying on variational methods, and an original thresholding procedure based on an iterative application of Otsu’s method. The segmentation of schlieren images, to get the contours of the spray vapour phase, is obtained by exploiting the surface curvature of the image to strongly enhance the intensity texture due to the vapour density gradients. This approach allows one to unambiguously discern the whole vapour phase of the spray from the background. Additional information about the spray liquid phase can be obtained by thresholding filtered schlieren images. The potential of this method has been substantiated in the segmentation of schlieren and scattering images of a GDI spray of isooctane. The fuel, heated to 363 K, was injected into nitrogen at a density of 1.12 and 3.5 kg m−3 with temperatures of 333 K and 573 K. [ABSTRACT FROM AUTHOR]