High-Speed X-Ray Imaging of Diesel Injector Needle Motion

Phase-enhanced x-ray imaging has been used to examine the geometry and dynamics of four diesel injector nozzles. The technique uses a high-speed camera, which allows the dynamics of individual injection events to be observed in real time and compared. Moreover, data has been obtained for the nozzles from two different viewing angles, allowing for the full three-dimensional motions of the needle to be examined. This technique allows the needle motion to be determined in situ at the needle seat and requires no modifications to the injector hardware, unlike conventional techniques. Measurements of the nozzle geometry have allowed the average nozzle diameter, degree of convergence or divergence, and the degree of rounding at the nozzle inlet to be examined. Measurements of the needle lift have shown that the lift behavior of all four nozzles consists of a linear increase in needle lift with respect to time until the needle reaches full lift and a linear decrease as the needle closes. For all four nozzles, the needle position oscillates at full lift with a period of 170–180 μs. The full-lift position of the needle changes as the rail pressure increases, perhaps reflecting compression of the injector components. Significant lateral motions were seen in the two single-hole nozzles, with the needle motion perpendicular to the injector axis resembling a circular motion for one nozzle and linear oscillation for the other nozzle. The two VCO multihole nozzles show much less lateral motion, with no strong oscillations visible.