Modeling and experimental validation of air-fuel ratio under individual cylinder fuel injection for port-injection engines

In internal combustion engines, air-fuel ratio is an important index. This paper aims to present a modeling approach for air-fuel ratio following the physical process in multi-cylinder port-injection engines. A linear periodic time-varying model is proposed with single input and single output. The model input is the fuel-injection command which is for an individual cylinder at its corresponding bottom dead center (BDC), and the model output is the sensed fuel-air ratio in the exhaust manifold. Lastly, the effectiveness of the presented model is validated by experiments. Experimental results show that the model output is close to the sensed fuel-air ratio.