Comparative Experimental Assessment of Methanol, Ethanol, and Butanol Fuels in a Spark-Ignition Engine: Combustion, Performance, and Emissions

This study experimentally investigates the combustion, performance, and emission characteristics of a spark-ignition engine fueled with single, dual, and ternary alcohol–gasoline blends under optimized ignition timing conditions. The tested fuels include single-alcohol blends containing 30% ethanol (E30), methanol (M30), and butanol (B30), a dual-alcohol blend (E15M15), and a ternary blend (E10M10B10), benchmarked against neat gasoline (G100). Experiments were conducted at constant operating conditions (75% load and 1500 rpm) while varying ignition timing. At the optimum ignition timing, all alcohol–gasoline blends exhibited significantly enhanced combustion intensity compared to G100. Relative to gasoline, B30 showed the largest increases in peak in-cylinder pressure and heat release rate (HRR), rising by 39% and 30%, respectively, followed by E30 (36% and 27%), M30 (24% and 21%), E15M15 (18% and 15%), and E10M10B10 (18% and 18%). In terms of engine performance, B30 achieved the highest brake power (+14% over G100); however, its efficiency was constrained by elevated in-cylinder temperatures (14% higher than G100) and increased thermal losses, resulting in a lower brake thermal efficiency (BTE) of 27%. In contrast, E30 recorded the highest BTE (30.3%), followed by M30 (29.6%), E15M15 (28.2%), E10M10B10 (28%), and G100 (24.5%). From an emissions perspective, the ternary E10M10B10 blend provided the most balanced outcome, achieving substantial reductions in hydrocarbon (HC) and NOx while limiting increases in carbon monoxide (CO) and carbon dioxide (CO₂) compared to single-alcohol blends.