Potential of double pilot injection strategies optimized with the design of experiments procedure to improve diesel engine emissions and performance

The substitution of the pilot-main injection schedule with the triple injection, for light engine loads and low engine speeds, has led to higher mean combustion pressures, lower heat release rates, shorter ignition delays and lower brake specific fuel consumption. Above all, a significant improvement in engine noise and in both CO and HC engine-out emissions has been achieved and the NOx emission have been limited by the application of high EGR rates. When medium engine loads and speeds are analyzed, the considered double-pilot injection strategy allows the NOx emissions to be reduced, compared to the baseline pilot-main injection schedule. However, the combustion noise does not improve and the soot deteriorates, even though the soot penalties are not relevant.