Abstract
Compared with conventional port fuel injection engines, fuel economy if GDI engine is significantly improved, but excessive NOx emission is generated at lean mode. TWC converts most HC and CO emissions to non-pollutant form during lean mode, but it is inefficient to treat NOx emission. So LNT is invented for NOx aftertreatment, which has both storage mode and purge mode. Excessive CO is sent out if purge time is too long and the stored NOX will not be fully converted if purge time is too short. To capture A/F ratio feedback information from the tailpipe, either
HEGO sensor or UEGO sensor can be used. In this paper, the mechanism inside the exhaust aftertreatment systems of Gasoline Direct Injection (GDI) engine is analyzed using chemical thermodynamics at first. Effects of O2 concentration, temperature and pressure on the orientations of LNT storage and purge reactions are presented. The basic models of three-way-catalyst (TWC) and lean NOx trap (LNT) are formulated based on actual physical characteristics. The utilization of universal exhaust gas oxygen (UEGO) sensor and heated exhaust gas oxygen (HEGO) sensor as well as the proposed approach for oxygen storage identification are discussed and compared. The oxygen storage effect has an essential impact on the management of LNT storage and purge operation, which also influences the fuel economy. Consideration of the O2 effects will be helpful for fuel economy improvement by the numerical simulations. An oxygen sensor based identification for LNT has been conducted, which is a theoretical attempt as an alternative approach to take the place of the expensive HEGO and UEGO sensors. In this paper, the exhaust aftertreatment systems of Gasoline Direct Injection (GDI) engine are analyzed using chemical thermodynamics. The basic models of three-way-catalyst (TWC) and lean NOx trap (LNT) are formulated based on actual physical characteristics. The utilization of universal exhaust gas oxygen (UEGO) sensor and heated exhaust gas oxygen (HEGO) sensor as well as the proposed approach for oxygen storage identification are discussed and compared. The oxygen storage effect has an essential impact on the management of LNT storage and purge operation, which also influences the fuel economy. An oxygen sensor based identification for LNT has been conducted, which is a theoretical attempt as an alternative approach to take the place of the expensive HEGO and UEGO sensors.