SUMMARY

The proposed thesis will use performance, emissions, and optical measurements to unravel the physical mechanics causing complicated operational trends in compression ignition (CI) engines equipped with a novel ducted fuel injection (DFI) system. Internal combustion engines make up the majority of vehicles. Emissions regulations make it prohibitively expensive for engine manufacturers to produce engines that simultaneously meets consumer demand and regulation requirements. One reason for this is the soot-NOx trade off that plagues CI engines. Exhaust gas recirculation (EGR) is the primary method of reducing NOx emissions. EGR lowers the oxygen concentration of the intake gas by recycling exhaust gasses back into the intake. This causes soot emissions to spike. A combustion strategy that can break this soot-NOx trade-off is needed. To meet this need, DFI was invented. DFI is an injection strategy that can be used to enhance fuel/charge-gas mixing in direct-injection CI engines. DFI injects fuel along the axis of a small tube in the combustion chamber. This promotes the formation of locally leaner mixtures in the autoignition zone relative to conventional diesel combustion. Evidence shows that DFI has potential to significantly reduce soot emissions in CI engines - it even can break the soot-NOx trade-off. Even so, implementation of DFI in engines has varied widely. Some authors have found multiple orders of magnitude reduction in soot emissions while others have found increased soot emissions. This shows that DFI has a failure mode, yet neither the mechanism of this failure nor the parameters that control it have been established. Furthermore, previous combustion strategies have been unable to operate at high-load. Identifying pathways for high-load DFI operation will be critical for the development of this technology. This work will address these gaps using a ducted, two- and four-orifice injector-tip assembly in a heavy-duty optically accessible research engine.