Control options for exhaust gas aftertreatment and fuel economy of GDI engine systems

Gasoline direct injection (GDI) engines have superiority over port fuel injection (PFI) engines on fuel economy at the expense of extra emissions, especially NOx. In lean operations, the traditional three-way-catalyst (TWC) is no longer effective for NOx aftertreatment. As a result, lean NOx trap (LNT) is introduced for the extensive NOx aftertreatment. In homogeneous operations, the HC and CO emission control technologies in PFI engines can be potentially selected. In comparison to TWC technology, LNT technology requires a higher-level integration into the GDI powertrain systems. Its operation switches between storage mode and purge mode. Mode switching has an impact on control of emission and fuel economy as well as driveability due to the rapidly changing mass air flowrate. Its frequency adversely affects fuel economy. A trade-off exists between fuel economy and the additional aftertreatment cost. Thermal management of LNT inquires a proper temperature window to trap NOx, to avoid thermal damage and to prevent NOx desorption. In this research, LNT thermodynamics mechanism is thoroughly investigated. NOx emission control is conducted and HC and CO emission control scheme is proposed. Along with emission control, fuel economy can be improved simultaneously by taking temperature factor and oxygen storage effect into account in LNT modeling and control design. On a basis of the fuel economy and emission improvement objective, the role of the oxygen storage effect on fuel economy is analyzed and simulated. In the meanwhile, the impact of trap temperature on LNT storage time, LNT purge time and fuel economy is examined. New technologies during cold start are suggested for HC and CO reductions.