Shadowgraph Tomography of a High Pressure GDI Spray

Abstract

An isooctane spray from a high-pressure multi-hole GDI injector (Bosch HDEV6) was characterized by means of optical extinction tomography, relying on parallel illumination by a focused-shadowgraph setup. The tests were carried out in air at ambient conditions at an injection pressure of 300 bar. Extinction images of the spray were acquired over a 180-degree angular range in 1-degree increments. The critical issues of optical extinction tomography of sprays, related to the strong light extinction by the dense liquid core of fuel jets, were addressed. To mitigate artifacts arising from the reconstruction process, the extinction data were subjected to spatially-variant filtering steps of both the raw and post-log data, before being analytically inverted through the inverse Radon transform. This made it possible to process extinction data for very large optical depths. A nearly complete three-dimensional reconstruction of the spray was obtained, providing significant details of the spray morphology and the internal structure of the jets throughout the spray development. The different phases of the atomization process from the near-field to far-field regions of the spray were observed.