Numerical Analysis of Passenger Car HSDI Diesel Engines with the 2nd Generation of Common Rail Injection Systems: The Effect of Multiple Injections on Emissions 2001-01-1068

A second generation of Common-Rail injection systems is coming into production making feasible multiple injection strategies. This paper aims to assess the capability of multiple injection in reducing NOx and soot emissions of HSDI Diesel engines. The analysis has been carried out at a characteristic point of the EUDC emission test cycle by using a customized version of the CFD code Kiva3, with updated sub-models developed by University of Bologna and University of Wisconsin. In particular, a recent modification has been introduced in the fuel conversion rate calculation in order to account for turbulence non-equilibrium effects. Different multiple injection profiles and combustion chamber configurations have been simulated and their effects on mixture formation, heat release rate and NO_x and soot formation have been analyzed. The main target was to comply with emission standards without significant loss in engine performance. Computational results seem to indicate that split injection is very effective in reducing NOx, while soot reduction is related to a better use of the oxygen available in the combustion chamber. Significant reduction of both NOx and soot engine-out emissions will be possible once next injector technology advances will reduce further the minimum delay between two consecutive injections allowing a more flexible injection timing. Investigation has revealed that traditional re-entrant bowls of car passenger HSDI Diesel engine perform well in conjunction with split injection since spray wall impingement is almost eliminated. As a consequence, the 2^nd generation of Common Rail injection system does not require large bowl diameter-to-bore ratio combustion chambers.