Model Prediction Control of Fuel-Air Ratio for Lean-Burn Spark Ignition Gasoline Engine

Abstract

Higher fuel economy and lower exhaust emissions for lean-burn spark-ignition (SI) engines depend significantly on precise fuel-air ratio (FAR) control. In addition, in order to improve fuel economy and reduce emissions, it is crucial for lean-burn engine to change the FAR according to different operating conditions. However, the presence of large time-varying delay due to the engine combustion, exhaust emissions transmission and lean NOx trap (LNT) module in the engine is the primary limiting factor in the control of FAR. Hence, the FAR prediction control algorithm based on disturbance observer is proposed in this paper. First, a predictive model with time-delay characteristic is established. Second, state observer is designed to predict the future dynamic changes of the engine system, and disturbance observer is designed to estimate and predict disturbances. Finally, the physical constraints of the engine and the FAR control requirements are transformed into the optimization objective function, and the optimization problem is solved online to get the amount of fuel injection. The results of Matlab and GT-Power co-simulation show that FAR predictive control algorithm based on the disturbance observer not only can quickly track the desired FAR, but also can achieve a large range of precise control of FAR and reduce the delay and parameter uncertainty impact on system dynamics.