A comprehensive analysis of combustion efficiency and emissions in biodiesel blends for sustainable energy solutions

The urgent global demand for clean and renewable fuels has intensified research into biodiesel production from non-edible oil feedstocks. Among them, Sterculia foetida and mango seed oils represent promising, underutilized resources. However, challenges such as inferior fuel properties and higher NOx emissions hinder their widespread adoption. To overcome these limitations, this study evaluates the performance, combustion, and emission characteristics of a biodiesel blend (BSM20) synthesized from Sterculia foetida and mango seed oils, modified with bio-based antioxidants derived from neem (NLA), eucalyptus (ELA), and Pongamia (PLA) leaf extracts. The biodiesels were blended with 20 % diesel and tested in a single-cylinder, four-stroke CI engine at varying loads. Physicochemical characterization showed improved cetane numbers (52–54) and flash points (137–140 °C), meeting ASTM D6751 standards. At full load, BSM20-NLA recorded the lowest BSFC at 0.488 kg/kWh, a 4.5 % improvement over BSM20 and only 1.2 % higher than diesel. BTE for BSM20-PLA reached 32.19 %, close to diesel's 33.04 %. CO and HC emissions decreased by 36.84 % and 22.22 %, respectively, while NOx emissions were reduced by 17.72 % for BSM20-NLA. Smoke opacity was lowered by 13.83 % with NLA. Combustion analysis revealed a 44.95 % shorter ignition delay and a peak pressure of 74 bar for BSM20-NLA, only 2.63 % below diesel. The rate of pressure rise (RPR) improved across all additive blends, indicating enhanced combustion efficiency. The addition of natural leaf additives also helped suppress oxidation and thermal degradation, improving fuel stability. These results demonstrate that incorporating plant-based antioxidants into biodiesel blends can significantly optimize engine performance and reduce environmental impact. Future research should focus on long-term engine wear analysis and scalability for commercial deployment.