Grigoriadis, Karolos M.Rao, Jagannatha R.Wilson, ChadYazji, Jalal2019-07-292019-07-292019-05https://hdl.handle.net/10657/4304Lean-burn operation in spark-ignition engines has shown promise in improving fuel economy and reducing harmful emissions in comparison with traditional stoichiometric operation. Close reference-tracking of the set air-fuel ratio profile is very crucial to healthy engine operation. What makes air-fuel ratio control challenging is the presence of a large variable time delay in the system's closed-loop, resulting mainly from the large distance traveled by the air-fuel mixture between the injection point and the exhaust. This thesis proposes modifications to an IMC-Smith predictor design employed to control the air-fuel ratio in a lean-burn engine. Matlab's Simulink provides a convenient platform to build dynamic models and simulate controllers, and for that reason, it is chosen to validate the proposed controller design and compare its performance to that of a PI controller and that of an IMC-Smith controller. Simulation results reveal the inadequacy of a basic PI controller in providing good reference tracking to a lean-burn profile. The proposed design shows very similar performance to a basic IMC-Smith controller in terms of overshoot and disturbance. However, its reduced settling time in comparison with the IMC-Smith controller (difference of up to 1.5s) renders it a more effective design at providing the desired level of reference-tracking.enThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).Honors Thesis