Andrew B. Swantek

X-ray Diagnostics for Cavitating Nozzle Flow

Cavitation plays a critical role in the internal flow of nozzles such as those used in direct fuel injection systems. However, quantifying the vapor fraction in the nozzle is difficult. The gas-liquid interfaces refract and multiply scatter visible light, making quantitative extinction measurements difficult. X-rays offer a solution to this problem, as they refract and scatter only weakly. In this paper, we report on current progress in the development of several x-ray diagnostics for cavitating nozzle flows. X-ray radiography experiments undertaken at the Advanced Photon Source at Argonne National Laboratory have provided measurements of total projected void fraction in a 500 μm submerged nozzle, which have been directly compared with numerical simulations. From this work, it has been shown that dissolved gases in the liquid also result in the formation of vapor regions, and it is difficult to separate these multiple phenomena. To address this problem, the liquid was doped with an x-ray fluorescent bromine tracer, and the dissolved air substituted with krypton. The fluorescent emission of Br and Kr at x-ray wavelengths provide a novel measurement of both the total void fraction and the dissolved gas component, allowing both cavitation and dissolved gas contributions to be measured independently. [199/200 words]

X-ray radiography of cavitation in a beryllium alloy nozzle

Making quantitative measurements of the vapor distribution in a cavitating nozzle is difficult, owing to the strong scattering of visible light at gas–liquid boundaries and wall boundaries, and the small lengths and time scales involved. The transparent models required for optical experiments are also limited in terms of maximum pressure and operating life. Over the past few years, x-ray radiography experiments at Argonne’s Advanced Photon Source have demonstrated the ability to perform quantitative measurements of the line of sight projected vapor fraction in submerged, cavitating plastic nozzles. In this paper, we present the results of new radiography experiments performed on a submerged beryllium nozzle which is 520 μm in diameter, with a length/diameter ratio of 6. Beryllium is a light, hard metal that is very transparent to x-rays due to its low atomic number. We present quantitative measurements of cavitation vapor distribution conducted over a range of non-dimensional cavitation and Reynolds numbers, up to values typical of gasoline and diesel fuel injectors. A novel aspect of this work is the ability to quantitatively measure the area contraction along the nozzle with high spatial resolution. Analysis of the vapor distribution, area contraction and discharge coefficients are made between the beryllium nozzle and plastic nozzles of the same nominal geometry. When gas is dissolved in the fuel, the vapor distribution can be quite different from that found in plastic nozzles of the same dimensions, although the discharge coefficients are unaffected. In the beryllium nozzle, there were substantially fewer machining defects to act as nucleation sites for the precipitation of bubbles from dissolved gases in the fuel, and as such the effect on the vapor distribution was greatly reduced.

Numerical investigation of liquid jet breakup and droplet statistics with comparison to X-ray radiography

In direct injection engines, the jet primary and secondary breakup processes have a significant influence on the fuel/air mixture formation and drop-size distribution directly affecting the fuel conversion efficiency and combustion characteristics. In this work the disintegration process of turbulent liquid jets from a realistic diesel injector issuing into a still environment is investigated numerically using a coupled liquid/gas interface capturing technique and a high-fidelity DNS/LES approach. This study is aimed at assessing the influence of NJFCP aviation jet fuel mixtures on the disintegration and droplet-size spray characteristics at simulated diesel operating conditions. For this purpose, an unstructured unsplit Volume-of-Fluid method is employed in conjunction with a realistic diesel injector geometry to simulate the pulsed jet disintegration and breakup process. Flow and droplet PDF statistics are extracted to demonstrate the impact of physical properties (A2, C3 fuel) on the mixing behavior and droplet distribution. The simulations are compared against X-ray radiography volume fraction measurements from Argonne National Laboratory and also serve as numerical benchmarks for calibration of lower fidelity models.

High-resolution X-ray tomography of engine combustion network diesel injectors:

The flow inside direct-injection diesel nozzles is strongly influenced by the local geometry. Deviations from the design geometry and nonuniformities along the fuel’s flow path can alter the expected spray behavior. The influence of small-scale variations in the internal geometry is not well understood due to a lack of data available to experimentalists and modelers that resolve such features. To address the need for more accurate geometry measurements that also quantify the error bounds on manufacturing variability, the 7-BM beamline of the Advanced Photon Source at Argonne National Laboratory has been customized to obtain high-resolution X-ray tomography of injection nozzles. In this article, we present results for several diesel injectors provided by the Engine Combustion Network. The imaging setup was optimized to measure dense metallic samples at high signal-to-noise ratio using projection imaging. To improve contrast, multiple images were recorded at each rotation angle. Phase shifting effects, which amplify the uncertainty in locating nozzle boundaries, were minimized by reducing the propagation distance of the X-rays between the nozzle and detector. Such improvements to the imaging technique enabled the nozzle hole diameter to be measured with an accuracy of 1.8 µm, which takes into account the pixel resolution as well as the properties of the imaging setup and the geometric analysis. The high spatial resolution allows the nozzle hole inlet corner radius to be azimuthally resolved. For the sample set under consideration, these new measurements reveal that non-hydroground injectors have a distribution of radii which typically vary by more than a factor of two. An azimuthally varying radius of curvature at the hole inlet is expected to result in highly asymmetric cavitation. Skeletal wireframe models of the nozzle hole geometries suitable for computational fluid dynamics mesh generation have been developed, in addition to full three-dimensional isosurfaces; these data have been made publicly available online.

A study on the relationship between internal nozzle geometry and injected mass distribution of eight ECN Spray G nozzles.

This research was performed at the 7-BM beamline of the APS at Argonne National Laboratory. Use of the APS is supported by the U.S. Department of Energy (DOE) under Contract No. DE-AC02-06CH11357. We gratefully acknowledge the computing resources provided on Blues, a high-performance computing cluster operated by the Laboratory Computing Resource Center at Argonne National Laboratory. We thank Dr. Doga Gursoy for the use of TomoPy and corresponding user support, as well as Dr. Xianghui Xiao at the APS 2-BM beamline for technical guidance in performing x-ray tomography. Argonne’s x-ray fuel injection research is sponsored by the DOE Vehicle Technologies Program under the direction of Gurpreet Singh and Leo Breton.

Synchrotron X-Ray Interrogation of Turbulent Gas–Liquid Mixing in Cryogenic Rocket Sprays

The atomization and vaporization of liquid jets within turbulent gaseous flows are characterized by the mixing phenomena occurring over a wide range of spatiotemporal scales. This creates a complex...