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Sketch and image of a prototype and research single-orifice fuel injector micronozzle. This study focuses on the tip part of the micronozzle where the fuel exits the orifice. The diameter of the orifice has a nominal value of . The shape and diameter of the sac and the thinned tip depends on the specific design.
Normalized absorption for a 3-mm-thick iron (solid line) and the minimum detectable thickness of iron for 1% (dotted line) and 2% (dashed line) absorption contrast as a function of x-ray energy.
Comparison of absorption-based and phase-enhanced radiography of a steel micronozzle: (a) absorption and (b) phase-enhanced images collected using 70 keV x-rays with sample-to-detector distances of 10 mm and 1.8 m, respectively, and 5 s exposure times (c) and (d) magnified views of the boxed regions in (a) and (b), respectively, (e) and (f) numerical simulations of the absorption and phase-enhanced images, respectively, for a model with parameters given in the text. The field of view in the magnified images (c) and (d) is . The arrows in (d) indicate the two regions with observable fabrication imperfections which cannot be resolved in the absorption-based radiograph (c). The ”zingers” in the images are due to x-rays hitting the CCD directly. They can be avoided by adding a mirror so that the CCD is not in-line with the beam.
Observed fabrication imperfections by phase-enhanced imaging: (a) an asymmetry in the shape of the sac in a ”hydroground” micronozzle (2 s exposure). The bright regions at the lower corners are artifacts due to sticking of an optical shutter in the detector for the no-sample reference image; (b) a machining imperfection in the sac-orifice transition region, indicated by the arrow (0.8 s exposure); (c) a machining imperfection (1 s exposure) in the same micronozzle as (b), but further back from the orifice, indicated by the arrow.
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