Utilizing co-pyrolysis oil from waste polypropylene and Calophyllum inophyllum seed in diesel engines: combustion,...

The rise in worldwide energy needs and growing environmental concerns necessitate the development of clean, renewable alternatives to fossil fuels. Co-pyrolysis of plastic waste and biomass provides a sustainable method for transforming waste into valuable fuel products. This study explores the engine performance, combustion behaviour, and emission properties of a single-cylinder, four-stroke compression ignition (CI) diesel engine fueled by blends of traditional diesel and co-pyrolytic oil produced through the co-pyrolysis of waste polypropylene (discarded saline bottles) and tamanu seed (Calophyllum inophyllum). Diesel was blended with 10%, 20%, 30%, and 40% co-pyrolytic oil by volume, labelled as B@10, B@20, B@30, and B@40, respectively, and tested in an unmodified diesel engine. Among the blends, B@40 exhibited the most promising performance, achieving a peak brake thermal efficiency (BTE) of 28.32% at full load, comparable to conventional diesel (D100). Moreover, B@40 exhibited a brake-specific fuel consumption (BSFC) of 0.29 kg/kWh, which is 14.7% lower than that of D100. B@30 demonstrated a slightly reduced exhaust gas temperature (EGT) of 328.78 °C, which was 0.99% lower than D100. CO and HC emissions increased with higher blend ratios but decreased with rising engine load, while NOx emissions declined with increasing blend ratios and rose with load. B@30 exhibited the most efficient emission performance, with CO, HC, and NOx emissions at 0.021%, 12%, and 189 ppm, respectively, showing a 5.9% reduction in NOx compared to D100. The blend also exhibited reduced heat release rates and in-cylinder pressure, reflecting improved combustion efficiency. These results demonstrate that co-pyrolytic oil is a promising, sustainable, and environmentally friendly substitute for conventional diesel fuel.