Diesel spray velocity and break-up characterization with dense spray imaging

International audienceThis work presents analysis methods for categorizing breakup morphology in a diesel spray produced by a single-hole, plain orifice diesel injector issuing into ambient atmospheric conditions. Velocity data and images which include the near-nozzle region of a diesel spray were obtained using both time-gated ballistic imaging (BI) and high-resolution ultrafast shadow imaging (USI) measurements. The USI results provide high-resolution visualization of the spray edges and resolved droplets within the depth-of-field of the collection optics, while the BI results provide a view of the spray at a modified dynamic range which mitigates interferences from refracted light and multiple-scattering noise, revealing additional spatial information. Time-correlated image-pairs obtained by both techniques were filtered and cross-correlated on a variety of scales to produce velocity profile data and identifiable structures which can be exploited to differentiate the breakup modes observed in the diesel spray. In addition, a multi-scale analysis was applied to the image data, demonstrating an approach whereby physical parameters can be derived from the image data to quantify the degree of atomization exhibited by a diesel spray

Diesel spray velocity and break-up characterization with dense spray imaging

International audienceThis work presents analysis methods for categorizing breakup morphology in a diesel spray produced by a single-hole, plain orifice diesel injector issuing into ambient atmospheric conditions. Velocity data and images which include the near-nozzle region of a diesel spray were obtained using both time-gated ballistic imaging (BI) and high-resolution ultrafast shadow imaging (USI) measurements. The USI results provide high-resolution visualization of the spray edges and resolved droplets within the depth-of-field of the collection optics, while the BI results provide a view of the spray at a modified dynamic range which mitigates interferences from refracted light and multiple-scattering noise, revealing additional spatial information. Time-correlated image-pairs obtained by both techniques were filtered and cross-correlated on a variety of scales to produce velocity profile data and identifiable structures which can be exploited to differentiate the breakup modes observed in the diesel spray. In addition, a multi-scale analysis was applied to the image data, demonstrating an approach whereby physical parameters can be derived from the image data to quantify the degree of atomization exhibited by a diesel spray

VELOCITY, INTERFACE COMPLEXITY AND DROPLETS PRODUCTION IN THE NEAR NOZZLE REGION OF A DIESEL SPRAY: COMPARISON BETWEEN EXPERIMENTAL ANALYSIS AND DIRECT NUMERICAL SIMULATION

International audienceA transillumination imaging arrangement using a double-pulsed femtosecond laser system coupled to a double frame camera was used to record high-resolution time-correlated image-pairs in the near-nozzle region of a high pressure Diesel jet. On the other hand, direct numerical simulations (DNS) using coupled volume of fluid/level set (VOF/LS) method for interface tracking have been carried out for this kind of injection. For the sake of precision of these numerical simulations, the flow inside the injector was also computed by using a commercial CFD code (Fluent 6.3). A quantitative comparison between numerical simulations and experimental images has been performed by applying the same tools. From the numerical point of view, some jet characteristics are well reproduced and this study allowed detecting the features that need improvement

Image processing techniques for velocity, interface complexity, and droplet production measurement in the near-nozzle region of a diesel spray

An ultrafast shadow imaging arrangement using a double-pulsed femtosecond laser system in concert with a frame transfer CCD was used to record time-correlated image-pairs in the near-nozzle region of a dissymmetric diesel jet issuing from a single-hole injector. A region-matching procedure was applied to produce velocity maps of the spray. The time-correlated image data were binarized and segmented to produce comparative data sets which isolate the jet core and the surrounding droplet cloud. The velocity mapping process was applied to these segmented data sets, a variable characterizing the degree of atomization of the jet was defined by means of statistical analysis, and the curvature scale space of the jet core edge was used to extract a measure of its complexity

NUMERICAL SIMULATION OF PRIMARY ATOMIZATION: INTERACTION WITH EXPERIMENTAL ANALYSIS

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