ID 309

High pressure Diesel fuel spray development: the effect of nozzle geometry and flow vortex dynamics

 

Abstract:

The transfer of future engine requirements on spray into the nozzle design is not a straightforward process in Diesel fuel injector nozzle development. One blocking point is a lack of detailed understanding on the mechanism and dynamics of the primary breakup process. Both cavitation and turbulence are known to be a significant mechanisms initiating the primary breakup process. It is still difficult to experimentally characterize the field turbulence inside a real-size injector nozzle. On the other hand, high resolution Large-Eddy-Simulation (LES) can be applied to resolve turbulence scales, and interface tracking techniques like Volume of Fluid (VOF) and level-set can be used to resolve the near-nozzle spray structure. Nevertheless, there are few published studies which take into account the complex nozzle flow dynamics under real application conditions for spray formation. Therefore, little is known on how the turbulence structure and dynamics trigger ligament and droplet formation in the primary breakup process. Delphi’s Advanced Injection and Combustion Center has carried out detailed investigation on the early Diesel spray development using up-to-date theoretical and experimental tools. For the convenience of the spray visualization, different 3-hole nozzles with contrasting injection hole geometric parameters were designed to facilitate this investigation. A high resolution X-ray Phase Contrast Imaging (PCI) technique has been applied for the characterization of the liquid-gas interface of the near-nozzle spray. For the theoretical investigation, ANSYS Fluent CFD software was used to predict the nozzle flow dynamics and the primary breakup process using the Large Eddy Simulation (LES) approach. Both new theoretical and experimental results demonstrated how the vortex dynamics in the nozzle flow triggers the liquid jet deformation and ligament formation as an important mechanism driving the early spray development. A number of examples will be presented to show how the nozzle geometry influences these vortex structures and dynamics.