Computational study of crevice soot entrainment in a diesel engine

In this reported work, operating parameters affecting spatial evolution of combustion soot and the associated 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 mesh domain comprised the crevice region to allow quantitative and qualitative inspections of species entrained into the crevice. Effects on the soot spatial evolution and the soot entrainment into crevice and region near the cylinder liner are studied for different injection strategies. This includes single injection with different start of injection (SOI) timings, as well as two main injection pulses with different fuel mass distribution and dwell period in between the two. Soot entrainment process is found to occur through two phases, which is after the ignition process and at the end of the expansion stroke. Most significant soot mass entrainment is found in cases with retarded fuel injection and split-main injection with large separation in between the pulses. Advancing the SOI reduces the soot concentration in the combustion chamber and correspondingly moderates the soot entrainment process. Implementing a close-coupled injection has a more significant effect in reducing soot entrainment in the late injection cases as compared to those with advanced injection. Amount of soot near the cylinder liner for all cases are between 20 and 2000 times higher than those in the crevice region, and soot entrainment via mass transport is dominant as compared to the soot formation near the crevice. For future investigation, improvement can be made to the CFD sub models to account for the thermophoretic effect on soot deposition process.