Adaptive air-fuel ratio control for spark ignition engines with time-varying parameter estimation

Abstract

Abstract-This paper presents a novel adaptive controller of air-fuel ratio (AFR) in spark ignition (SI) engines. The controller robustly estimates unknown time-varying engine parameters and thus improves both the transient and steady-state performance. The objective is to regulate the AFR in the combustion chamber around the stoichiometric value by manipulating the injected fuel mass flow rate so as to improve fuel economy and to reduce emissions. The AFR regulation problem is first reformulated into a tracking control problem of the fuel mass flow. This simplifies the control synthesis, i.e. the number of parameters to be online updated can be reduced. Then a representation of the parameter estimation error is derived by using auxiliary filter operations, which is used as a new leakage term in the adaptive law. In this case, exponential convergence of the AFR error and the estimation of the time-varying parameters can be proved simultaneously. The proposed controller is compared with a generic adaptive controller using the gradient descent method based on a well-calibrated mean value engine model (MVEM). Finally, the proposed controller is also validated with a commercial engine simulation software, GT-Power, demonstrating better results for the suggested adaptive controller than for the gradient descent approach.

Nonlinear Observer-Based Air-Fuel Ratio Control for Port Fuel Injected Wankel Engines

“…the control command for the fuel injector) and χ, 0 ≤ χ < 1, is a fraction of injected fuel that deposited on the manifold wall as fuel puddles. It should be noted that the fuel puddle model (6)(7) is perceived to be more correct compared to our previous version in [5] since it considers the effect of the fuel puddle flow (Couette flow) entering the chamber.…”

“…It has been shown in our previous work [5] that the AFR regulation problem can be reformulated into a fuel flow tracking problem for the sake of design simplicity. Then the feedback control error e used in the AFR controller can be defined as…”

“…However, the conversion efficiency of TWC is fairly sensitive to AFR, which is required to be regulated around the stoichiometric value (e.g. 14.67 for petrol) [5]. Moreover, combustion with a stoichiometric AFR is essential to achieving the optimal thermal efficiency and dynamic performance.…”

“…This motivates the research on advanced AFR control design such as optimal control [7], robust control [8][9], adaptive control [5] [10], and more recently, observer-based control [6] [11]. An optimal AFR controller was designed in [7] considering the cyclic variations of residual gas.…”

“…Then, robust techniques such as H ∞ control [8] and sliding mode control [9] were proposed to regulate the AFR in the presense of external disturbance. In order to deal with parameter uncertainties, adaptive approaches were presented to address air-filling dynamics in [5] and time delay dynamics in [10]. However, the complexity of the adaptive controller limits their practical implementation.…”