This study investigates experimentally and numerically the impact of e-ethanol drop-in on combustion, performance, and emission metrics in a single-cylinder spark ignition engine. Experiments were conducted at a constant compression ratio of 9, 75% throttle, engine speed of 1500 RPM, equivalence ratio of 0.81 and fixed ignition timing of 25° CAD BTDC. Numerical simulations utilizing both a global single-step reaction model for pure gasoline (G100) and a detailed chemical mechanism for G100 and different ethanol blends provided accurate predictions of combustion trends. Blending ethanol up to 30% by volume (E30) enhances combustion quality, as evidenced by increased in-cylinder pressures and improved IMEP. However, ethanol concentrations beyond E40 led to combustion instability and significant losses in pressure and efficiency due to sub-optimal combustion phasing supported by lower heating value. The analyses of the thermal and flow fields revealed consistent intake-induced tumble motion and similar in-cylinder velocity structures for E100 and G100, regardless of blend ratio. E30 offered the lowest indicated specific fuel consumption (ISFC) of 380 g/kWh and the highest indicated thermal efficiency 〖(η〗_(th,I)) of 34.5%. Emission trends favored ethanol addition, with reductions in CO2 by 16%, CO by 27%, NOx by 38%, and unburned hydrocarbons by 57% for E60 in comparison with G100 attributing to ethanol's oxygenation.