Abstract
Implementation of a crevice model (CM) is important for the simulation study of soot mass entrainment into engine oil via crevice flow, especially when examining the detailed influence of in-cylinder processes on this. In this reported work, operating parameters affecting spatial evolution of combustion soot and the associated bulk gas transport processes into crevice region in a light-duty diesel engine were appraised. Numerical computation of diesel combustion was undertaken by means of linking a plug-in chemistry solver namely, CHEMKIN-CFD into ANSYS FLUENT 12, a commercial Computational Fluid Dynamics (CFD) software. The chemical reactions mechanism of n-heptane surrogate fuel was integrated with the Eddy-Dissipation Concept (EDC) model to represent turbulent-chemistry interaction of the fuel oxidation process. Discrete phase model of the Lagrangian approach was employed to represent the particles of liquid fuel spray dispersed in the continuous phase, with a hybrid spray atomisation model, Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) implemented to model fuel spray breakup. The computation mesh comprised the crevice region to allow quantitative and qualitative inspections. With the CM activated, an increase in soot mass entering the crevice region was noted due to higher velocities induced at the vicinity of the crevice region by this transport mechanism. The pressure difference between the combustion chamber and crankcase generates the flow of mass charge through the crevice region. Effects on the soot spatial evolution are studied for different injection strategies, which include single injection with different start of injection (SOI) timings, as well as split main injection with different dwell period. Most significant soot mass entrainment into the crevice volume was found in cases with retarded fuel injection and split main injection with large separation in between the pulses.
KEYWORDS Computational Fluid Dynamics, light-duty diesel engine, diesel combustion, soot entrainment, crevice flow