Predicted Paths of Soot Particles in the Cylinders of a Direct Injection Diesel Engine

Soot formation and distribution inside the cylinder of a light-duty direct injection diesel engine, have been predicted using Kiva-3v CFD software. Pathlines of soot particles traced from specific in-cylinder locations and crank angle instants have been explored using the results for cylinder charge motion predicted by the Kiva-3v code. Pathlines are determined assuming soot particles are massless and follow charge motion. Coagulation and agglomeration have not been taken into account. High rates of soot formation dominate during and just after the injection. Oxidation becomes dominant after the injection has terminated and throughout the power stroke. Computed soot pathlines show that soot particles formed just below the fuel spray axis during the early injection period are more likely to travel to the cylinder wall boundary layer. Soot particles above the fuel spray have lesser tendency to be conveyed to the cylinder wall. The upper part of the cylinder liner seems to be the most vulnerable to soot transfer to the wall layer. This soot is formed at the early crank angles after the start of injection, e.g., 8° ATDC. Soot generated at later crank angles, e.g., 18° ATDC, swirls around the combustion chamber following the piston in the expansion stroke and does not come near the cylinder wall. If nucleation was retarded soot transfer to the cylinder liner boundary layer could be reduced.