Unveiling the Role of Methanol, Ethanol, and Butanol Additives in a Spark-Ignition Engine: Combustion, Performance, and Emission Metrics

The growing need for cleaner transportation fuels has intensified interest in renewable oxygenated additives for spark-ignition (SI) engines. This study investigates the comparative effects of three oxygenated alcohols, methanol (M30), ethanol (E30), and butanol (B30), blended at 30% by volume with gasoline, on combustion, performance, and emission behaviors of an SI engine. Experiments were conducted on a single-cylinder, four-stroke, port-fuel-injected engine at 1500 rpm under 50% and 75% load conditions. The results showed that B30 produced the most advanced pressure peaks, reaching 17 °CA at 75% load, while E30 showed delayed combustion. M30 achieved the highest brake thermal efficiency at 29.6%, a 10.4% increase over gasoline. E30 delivered the greatest brake power increase (10.1% at 75% load), and reduced hydrocarbons and nitrogen oxides emissions by over 40% and 26.5%, respectively. However, all alcohol blends showed elevated carbon dioxide emissions (up to 25% for B30) and brake specific fuel consumption (M30 increased by 24.3% at 75% load).