Numerical Investigation of the Fuel/Air Ratio Sensor Sensitivity in a Port-Fuel-Injected Spark-Ignition Engine Equipped With Three-Way Catalysts

Abstract

The internal combustion engine will continue to be the primary source of power for transportation. Spark ignition (SI) engines are still widely used for mobility due to their wide range of operating conditions. The key operating variables of an engine are primarily controlled by an engine control unit that has been calibrated. However, a less accurate sensor can lead to large variations in engine performance and emissions. The purpose of this study was to investigate the importance of air–fuel ratio sensor precision during operation of various engines. In this study, a one-dimensional (1D) computational fluid dynamics (CFD) model was used to analyze the engine response due to the variation of the equivalence ratio sensor precision at different engine speeds and loads, to explore the main indicators influenced by the precision of equivalence ratio measurements, and to propose a discriminant criterion for evaluating the suitability of the proposed equivalence ratio precision in relation to the conversion rate of three-way catalyst and vehicle emissions. The results show that for engine performance, it varies slightly with small changes in the fuel-to-air ratio. At higher engine speeds, a slight change in the air–fuel ratio leads to a smaller change in emissions. At the same time, changes in fuel-to-air ratio have a significant effect on carbon monoxide (CO) and nitrogen oxides (NOx) emissions. Carbon monoxide is the most sensitive to the air–fuel ratio, followed by nitrogen oxides, while unburned hydrocarbons are not sensitive to it. And for the three measurement accuracies studied in this paper (0.5%, 1%, and 2%), the accuracies are acceptable, but combining the relative errors of the actual emissions of CO and in order to achieve accurate combustion control, it is recommended that the sensor accuracy should be at least higher than 1% for the port fuel injected engine investigated in this study.