This paper presents a thorough analysis of the exhaust gas aftertreatment systems of Gasoline Direct Injection (GDI) engines. The mechanism of the exhaust gas aftertreatment systems is investigated using chemical thermodynamics. The physical models of three-way-catalyst (TWC) and lean NOx trap (LNT) are presented. The objective is to propose an alternative approach for the identification of A/F ratio and oxygen concentration in the exhaust systems to substitute the costly oxygen sensors. A simple control scheme is included within the model identification and prediction results are compared with the testing data from the universal exhaust gas oxygen (UEGO) sensor and from the heated exhaust gas oxygen (HEGO) sensor. The oxygen storage effect has an essential impact on the LNT storage and purge operations, which will also affect the overall fuel economy of GDI engine systems. Its influence on the fuel economy has been estimated by numerical simulations, which is correspondent to the extra percentage of fuel consumption.

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