The effect of tamanu oil and oxygenated additives on spark-ignition engine performance and emissions

A B S T R A C T The growing demand for low-emission and eco-friendly fuels has encouraged the development of multicomponent oxygenated blends for spark-ignition engines. This study evaluates the performance and emission characteristics of a single-cylinder, four-stroke gasoline engine with a 9.5:1 compression ratio using a newly formulated fuel blend called PBBT (Pertasol–n-Butanol–Butoxyethanol–Tamanu oil). The blend consists of 5% n-butanol, 5% 2-butoxyethanol, and 2–10% tamanu oil mixed into a Pertasol base. Experiments were conducted at engine speeds between 4000 and 9000 rpm under controlled conditions using a 50-L dynamometer and a four-gas analyzer. The results indicate notable improvements compared with conventional gasoline: the PBBT-5 blend achieved the highest thermal efficiency of 22.74% (a 44.4% increase), while CO and HC emissions decreased by more than 30%. NOx emissions were reduced by up to 15.40% with higher tamanu oil content. These improvements are attributed to the oxygenated components, which enhanced mixture homogeneity, combustion stability, and reduced peak combustion temperatures. Overall, the findings show that PBBT is a promising, cost-effective, and environmentally beneficial alternative fuel for spark-ignition engines.