COMPUTATIONAL INVESTIGATION OF COMBUSTION PHASING AND EMISSIONS FOR GDCI ENGINE OPERATIONS

The gasoline direct-injection compression-ignition (GDCI) combustion strategy is studied in this work based on the numerically constructed ignition phase curves. Previous research has shown that for GDCI operation, the engine efficiency can reach as high as that of diesel engines yet the NOx and soot emissions can be reduced simultaneously. A comparison between GDCI and diesel operation is made by investigating two combustion regimes, partially premixed combustion (PPC) and conventional direct-injection compression-ignition (DICI). The injection timing, which determines the controllability of GDCI operation, spans over a wide range to study its effect on the combustion phasing. Fundamental processes, such as fuel evaporation, transport, and ignition are used to explain the differences between these two operating regimes. Finally, the effects of heating intake air, boosting intake air pressure, applying warm EGR are also studied. The emissions are correlated to the instantaneous parameters of the mixture at the moment of ignition, providing insights about the fundamental mechanisms of the emission reduction by adopting GDCI combustion.