Supervisory optimization of ethanol–gasoline blend ratios in spark-ignition engine using coupled GT-Power and MATLAB/Simulink simulation

The growing demand for energy and the environmental impacts associated with fossil fuels have increased interest in renewable alternatives such as ethanol for spark-ignition (SI) engines. Although ethanol–gasoline blends are widely used, a single fixed blend ratio cannot be considered optimal over the entire operating range of an engine. In this study, a numerical framework is developed to determine speed-dependent optimal ethanol–gasoline blend ratios for a single-cylinder SI engine operating under steady-state full-load conditions. A one-dimensional engine model is first developed in GT-Power and validated using experimental data obtained with pure gasoline. The validated model is then coupled with MATLAB/Simulink, where a quasi-steady supervisory control and optimization algorithm is implemented. The optimization procedure, based on the fmincon algorithm, aims to maximize ethanol substitution while limiting power deviation and simultaneously reducing brake specific fuel consumption (BSFC), carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions. Simulations are performed at engine speeds between 2000 and 3000 rpm with ethanol fractions ranging from 0% to 50%. The results indicate that ethanol contents above 50% lead to unstable engine behavior under fixed ignition timing. Moreover, the optimal ethanol fraction increases with engine speed, reaching up to 28% at 3000 rpm, while the associated power loss remains below 3%. Overall, the proposed framework provides a quasi-steady optimization approach for adapting fuel blend ratios to engine operating conditions and may serve as a foundation for future development of real-time fuel blending strategies in SI engines.