X-Ray Tomography of High Pressure Fuel Spray by Polycapillary Optics

The study of transient high pressure fuel sprays by X-ray based techniques is worldwide diffused. Synchrotron radiation is successfully exploited for this aim because of its high intensity and pulsed nature. However top-table application are unusual. This work reports the structure of a gasoline spray from an automotive GDI injection system obtained by X-ray Tomography desktop experiments using an 8 keV Cu K alpha X-ray. Polycapillary semilens shaped the divergent X-ray beam into quasi-parallel one allowing to focus the radiation on the investigated spray region. High contrast focus images were collected by a CCD detector for X-radiation. A 6-hole GDI injector has been coupled to the high pressure pump by a specially designed rotating device able to work up to 25MPa. X-ray absorption measurements have been performed with angular steps Delta theta = 1 degrees at the injection pressure of 12.0 MPa. The sinogram reconstruction of the jets by slices permitted to get information about the inner structure of the fuel spray downstream the nozzle tip, where conventional optical techniques are inhibited. A 3D spatial distribution of the fuel emerging from the injector has been obtained. The data have been used to perform spray density measurements. The results concerning the absorption profile along the fuel jets axis and the cross section distribution at different distances from the nozzle have been reported.