Shadowgraph tomography of a high-pressure GDI spray

An isooctane spray from a high-pressure multihole GDI injector (Bosch HDEV6) was characterised by means of optical extinction tomography, relying on collimated illumination by a focused shadowgraph setup. The tests were carried out in air under ambient conditions at an injection pressure of 300 bar. Spray images 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 artefacts arising from the reconstruction process, the extinction data were subjected to spatially-variant filtering steps for both raw and post-log data before being analytically inverted through the inverse Radon transform. This approach made it possible to process extinction data at 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 spray development. Different phases of the atomization process, from the near-field to the far-field regions of the spray, were observed.