Comparative Analysis of Thermal Efficiency in Otto Engines Using E20 and Pertalite Fuels

This study aims to analyze the influence of fuel type on the thermal efficiency of the four-stroke Otto engine, by comparing the use of Pertalite (RON 90) and E20 (a mixture of 20% ethanol and 80% gasoline). The research was conducted experimentally at the Combustion Motor and Renewable Energy Laboratory using a single-cylinder gasoline engine with a capacity of 125 cc at a load variation of 25%, 50%, 75%, and 100%. The parameters observed included torque, power, specific fuel consumption (BSFC), thermal efficiency, exhaust gas temperature, and CO and HC gas emissions. The test results show that E20 fuel produces performance that is almost equivalent to that of Pertalite. The maximum power of E20 only decreases by about 2–3%, while its thermal efficiency reaches 28.4%, close to Pertalite's efficiency of 29.1%. The consumption of E20-specific fuels is slightly higher (about 5–7%) due to the lower calorific value of ethanol, but this is offset by a more complete combustion and a significant reduction in exhaust emissions. CO emissions decreased by 30%, and HC decreased by about 25%, while the average exhaust gas temperature was 20–30 °C lower than Pertalite. The results of the statistical test showed no significant difference in thermal efficiency between the two fuels (p = 0.087 > 0.05). Overall, E20 proved to be feasible for use on conventional Otto engines without major modifications, and supported efforts to transition to clean and sustainable energy in Indonesia.