Study on a closed-loop air-fuel control system of gasoline engines by simulation

In order to study the factors that influence the air-fuel ratio(A/F), the amplitude and frequency of A/F fluctuation, to reform the control strategy, and to improve the efficiency of three-way catalyst(TWC), a model of closed-loop control system including the engine, air-fuel mixing and transportation, oxygen sensor and controller, etc., is developed. Various factors that influence the A/F control are studied by simulation. The simulation results show that the reference voltage of oxygen sensor will influence the mean value of A/F ratio, the controller parameters will influence the amplitude of A/F fluctuation, and the operating conditions of the engine determine the frequency of A/F fluctuations, the amplitude of A/F fluctuation can be reduced to range of demanded values by logical selection of the signal acquisition method and controller parameters. Higher A/F fluctuation frequency under high speed and load can be reduced through software delay in the controller. The A/F closed-loop control system based on the simulation results, accompanied with a rare-earth element TWC, gives a better efficiency of conversion against harmful emissions.