This paper presents a modeling approach for describing the dynamics from the fuel injection command of individual cylinders to the oxygen sensor output in spark-ignition multicylinder engines. In the presented approach, it is shown that the dynamics can be modeled as a single-input, single-output, periodic time-varying system, in which the periodicity is attributable to the cyclically physical phenomenon of the engine system. Furthermore, as compared to the conventional air-fuel ratio model,

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... proposed model provides the characteristics of the air-fuel ratio in a small-scale sampling rate under individual cylinder fuel injection. To demonstrate the effectiveness, numerical simulation results are presented, and finally, experimental validation is provided on the basis of the results of the identification tests conducted on a six-cylinder gasoline engine control test bench.