Air-fuel ratio control in gasoline engines based on state estimation and prediction using dynamic models

A highly accurate air-fuel ratio control scheme has been developed for reducing exhaust emissions from gasoline engines. It uses a compensation scheme based on state estimation and prediction to cope with the problems of precisely detecting the amount of air flowing into the cylinder, which is difficult in transition due to air-flow sensor delay, air charging of the intake manifold, and a control structure that requires predicting the air flow one stroke ahead, and the delay in fuel transport caused by the fuel on the wall of the intake manifold. The internal state variables, the manifold pressure, the air flow rate at the inlet port, and the fuel film amount are estimated using a previously adjusted dynamic model, the fuel injection amount is controlled based on these estimated values so that the target air-fuel ratio can be accurately achieved. Experiments showed that the air-fuel ratio control is improved, reducing exhaust emissions from 10% to 35% compared with the conventional method