Abstract
The multiphase flow inside a diesel injection nozzle is imaged using synchrotron X-rays from the Advanced Photon Source at Argonne National Laboratory. Through acquisitions performed at several viewing angles and subsequent tomographic reconstruction, in-situ 3D visualization is achieved for the first time inside a steel injector at engine-like operating conditions. The morphology of the internal flow reveals strong flow separation and vapor-filled cavities (cavitation), the degree of which correlates with the nozzle’s asymmetric inlet corner profile. Micron-scale surface features, which are artifacts of manufacturing, are shown to influence the morphology of the resulting liquid-gas interface. The data obtained at 0.1 ms time resolution exposes transient flow features and the flow development timescales are shown to be correlated with in-situ imaging of the fuel injector’s hydraulically-actuated valve (needle). As more than 98.5% of the X-ray photon flux is attenuated within the steel injector body itself, we are posed with a unique challenge for imaging the flow within. Time-resolved imaging under these low-light conditions is achieved by exploiting both the refractive and absorptive properties of X-ray photons. The data-processing strategy converted these images with a signal-to-noise ratio of ~ 10 into a meaningful dataset for understanding internal flow and cavitation in a nozzle of diameter 200 μm enclosed within 1–2 millimeters of steel.
Highlights
The multiphase flow inside a diesel injection nozzle is imaged using synchrotron X-rays from the Advanced Photon Source at Argonne National Laboratory
In contrast to visible light, X-ray diagnostics are not limited by the opacity of a steel injector body as has been demonstrated in previous studies where line-of-sight imaging was conducted inside diesel injector nozzles without any optical access[12,13]
In 2017, Matusik et al.[1] conducted high-resolution X-ray tomography of diesel injector nozzles openly shared for research purposes within the Engine Combustion Network (ECN)[20] and showed that walls of the flow orifices were rich in micron-scale surface features
Summary
A key limitation of many of previous studies employing 3D X-ray imaging is that the nozzle material, size and operating conditions were not representative of practical injectors, considering typical diesel nozzles are made from steel, have diameters of 100–200 μm, and operate at injection pressures of 100–200 MPa. In 2017, Matusik et al.[1] conducted high-resolution X-ray tomography of diesel injector nozzles openly shared for research purposes within the Engine Combustion Network (ECN)[20] and showed that walls of the flow orifices were rich in micron-scale surface features. The flow-field is reconstructed from X-ray projections collected at various angles acquired from several injection events, resulting in time- and ensemble- averaged snapshots which do not capture stochastic phenomena such as string cavitation or shedding/ collapse This is an inherent limitation in any work that uses computed tomography[17,18,19]. Regardless of these constraints, some of the persistent effects on flow morphology due to surface features and geometric variabilities that occur during manufacturing can still be observed, yielding valuable information
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