Computational Analysis of Spray Formation in Large Two-Stroke Marine Diesel Engine Atomizers

Abstract

Large two-stroke marine diesel engines have special injector geometries which differ substantially from the configurations used in most other diesel engine applications. In particular, injector orifices are distributed in a highly nonsymmetric arrangement, thus affecting the spray characteristics. In this study, a new approach was implemented in computational fluid dynamics (CFD) simulations of these sprays, for nonevaporating conditions, for one noneccentric and two eccentric atomizers. The approach consisted of modeling spray primary breakup using large eddy simulation (LES), and modeling spray secondary breakup by means of Reynolds-Averaged Navier–Stokes (RANS) equations in conjunction with validated spray models. LES results were processed using a new droplet identification method, yielding probability density functions (PDFs), which were used as input in the secondary breakup simulations. Spray morphology was characterized in terms of penetration length, deflection angles, and spray cone angles. Results were in good agreement with those of recent experiments in a large spray combustion chamber, verifying strong deviation from an axisymmetric spray structure; they outperformed CFD results using a conventional (RANS-only) method. Overall, the present approach was shown to be effective for CFD studies of asymmetric sprays in large marine engines.