Air-to-fuel ratio (AFR) is the mass ratio of air and fuel trapped inside a cylinder before combustion begins, and it affects engine emissions, fuel economy, and other performances. For a dual fuel engine equipped with both port-fuel-injection (PFI) and direct injection (DI) systems, the fuel ratio is the ratio of the first fuel and total fuel masses. In this research, a multi-input-multi-output sliding mode control scheme is developed with guaranteed stability to simultaneously control air-to-fuel and fuel ratios to desired levels under various air flow disturbances by regulating the mass flow rates of engine PFI and DI injection systems. A state estimator with varying parameter gain is designed with guaranteed stability to allow implementation of the proposed state feedback sliding mode controller into a Hardware-In-the-Loop (HIL) simulation environment, where the sliding mode control strategy is implemented into a production engine control module ("hardware"). The sliding mode control performance was compared with a well-tuned baseline multi-loop PID controller through HIL simulations and showed improvements, where HIL simulations were conducted to validate the feasibility of utilizing the developed controller and state estimator for automotive engines.A dynamic linear quadratic (LQ) tracking controller is developed to regulate the transient AFR based upon a control oriented model of the engine PFI wall wetting dynamics and the transport delay between the measured air flow and manifold. The LQ tracking controller is designed to optimally track the desired transient AFR by minimizing the error between the trapped in-cylinder mass and the product of the desired AFR and fuel mass over a given time interval. The performance of the optimal LQ tracking controller was compared with the conventional transient fueling control based on the inverse fueling dynamics through simulations and showed improvement over the baseline conventional inverse fueling dynamics controller. To validate the control strategy on an actual engine, a 0.4 liter single-cylinder direct-injection engine was used. The PFI wall-wetting dynamics were simulated in the engine controller after the DI injector control signal. Engine load transition tests for both DI and simulated PFI cases were conducted on an engine dynamometer, and the results showed improvement over the baseline transient fueling controller based on the inverse fueling dynamics.
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