Mixture strength control system effectiveness depends on its capacity to deal with air and fuel transport processes inside the intake manifold: the prediction of air mass flow to the engine cylinders and the compensation for the fuel lag during engine transients. These issues are all likely to be of extreme importance with the transient air/fuel ratio control strategies. This paper introduces an innovative model-based air/fuel ratio control strategy for SI engines. It is based on a previously published modeling approach for the air dynamics inside intake manifolds, which is based on the formulation of the mass, momentum and energy conservation equations and named as Method Of Interconnected Capacities. The proposed strategy uses a fuel compensator that is based on a macroscopical modeling of the fuel film dynamical behavior inside the intake manifold, which is derived from the Aquino model. A wide range of severe transient tests obtained from the experimentation of a single-cylinder research engine (type AVL 5401), equipped with port-fuel injection system, is presented. The results obtained have proved the effectiveness of the proposed strategy in controlling the air/fuel ratio in SI engines in a better way compared to the traditional control systems.

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