To maintain the stoichiometric air-fuel ratio (AFR), this paper presents a model-based adaptive AFR control scheme for port-injected spark ignition engines. The utilized mean-value model in control design accounts for the impingement and the evaporation process of the injected fuel on the walls and calculates on the uncertainties in the dynamics of the intake manifold and crankshaft rotation. A fueling controller with adaptive update laws is derived for estimating the uncertain parameters related to inaccuracies in air flow and fuel delivery into the cylinders and engine torque production, which is implemented by utilizing engine speed, manifold pressure and temperature, air mass flow rate at the throttle, and the universal exhaust gas oxygen (UEGO) sensor information, without knowledge of the fuel flow mass. Theoretical analysis shows that the proposed strategy is able to regulate the AFR against the parameter uncertainties. Moreover, both simulation and experiment on an engine test bench demonstrate the capability of the adaptive controller to recover the performance and robustness properties of the control system in the presence of various operating conditions and uncertainties including air path and fuel path perturbations and load torque disturbance as well.

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