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A Novel Approach to Assess Diesel Spray Models using Joint Visible and X-Ray Liquid Extinction Measurements
Abstract:
Spray processes, such as primary breakup, play an important role for subsequent combustion processes and emissions formation. Accurate modeling of these spray physics is therefore key to ensure faithful representation of both the global and local characteristics of the spray. However, the governing physical mechanisms underlying primary breakup in fuel sprays are still not known. Several theories have been proposed and incorporated into different engineering models for the primary breakup of fuel sprays, with the most widely employed models following an approach based on aerodynamically-induced breakup, or more recently, based on liquid turbulence-induced breakup. However, a complete validation of these breakup models and theories is lacking since no existing measurements have yielded the joint liquid mass and drop size distribution needed to fully define the spray, especially in the near-nozzle region.
In this work, we compare physical models of aerodynamically-induced and turbulence-induced spray breakup and assess their influence on predictions of local spray behavior using 3D CFD simulations in CONVERGE. Motivated by these results, we propose a new spray model validation methodology, using a combination of quantitative measurements and light-scatter modeling, to help fully validate the joint liquid mass and mean drop size distribution in predicted sprays. In particular, we demonstrate that employing joint x-ray and visible liquid extinction measurements, in combination with light extinction modeling within the predicted spray, can provide unique evaluation of the predicted spray morphology and ensure a more accurate representation of the experimentally measured spray.