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

The use of Wankel engines has been severely limited as the emission regulations get stringent around the world since the 1970s. The fuel puddles due to port fuel injection (PFI) and the leakage between combustion chambers are significant sources of efficiency loss and emissions. For most spark ignition engines in production, the emission strongly depends on the air-fuel ratio (AFR) controller in cooperation with a three-way catalytic (TWC) converter. This paper presents a generic observer-based AFR control framework to deal with the high nonlinearities of Wankel engines so as to improve the fuel economy and emissions. By taking the unknown parameters as augmented engine states, an extended Kalman filter is designed to estimate the fuel puddle dynamics using only mass air flow (MAF) and lambda sensors. The complex nonlinear air-filling dynamics are lumped together and estimated using novel observer techniques. A newly proposed unknown input observer is compared with a dirty differentiation observer and then employed in the feedback AFR control design. Comparative simulations based on a calibrated benchmark engine model show that the proposed control can speed up the transient response and regulate the AFR around the stoichiometric value.