High Resolution Numerical Simulations of Primary Atomization in Diesel Sprays with Single Component Reference Fuels

A high-resolution numerical simulation of jet breakup and spray formation from a complex diesel fuel injector at diesel engine type conditions has been performed. A full understanding of the primary atomization process in diesel fuel injection has not been achieved for several reasons including the difficulties accessing the optically dense region. Due to the recent advances in numerical methods and computing resources, high resolution simulations of atomizing flows are becoming available to provide new insights of the process. In the present study, an unstructured un-split Volume-of-Fluid (VoF) method is employed to simulate the injection event with prescribed bulk inflow conditions. An axial single-hole ARL fuel injector was X-ray scanned at The Advanced Photon Source Facility from Argonne National Laboratory for this work to define the internal geometry. The working conditions correspond to orifice dimensions of 90μm fueled with n-paraffin (n-dodecane) and iso-paraffin (iso-octane) reference fuels for a detailed investigation of fuel specific mixing mechanisms. The spray releases into a quiescent chamber filled with 100% Nitrogen at ambient conditions at 20 bar, 300K with 6.9x10 < Re < 2.5x10 and 5.4x10 < We < 1.25x10 both with Oh > Ohcr setting the spray in the full atomization mode. The simulations provide detailed diagnostics in the optically dense region extending from 5 < x/d < 25 jet diameters. The results provide insights on the effect of start-of-injection on the velocity and volume fraction fields for each fuel at a range of pressures. High resolution backlit imaged data in the near nozzle region recently acquired at the Army Research Laboratory are used to provide validation metrics for the spray breakup length and dispersion characteristics.