Development of liquid biofuel properties through the blending of biodiesel from used cooking oil and pyrolysis oil from low-quality rubber waste

Abstract

This study explores the potential of enhancing waste rubber pyrolysis oil (WRPO) by blending it with biodiesel derived from used cooking oil (WCO biodiesel oil) to improve its suitability as an alternative biofuel. The hypothesis posits that such blending will improve fuel stability, reduce acidity, and enhance combustion efficiency. The methodology included fuel characterization, preparation of various blending ratios, and evaluation of fuel properties, engine performance, and emissions. WRPO was found to contain high levels of aromatic and oxygenated compounds, resulting in high acidity (0.48 mg KOH/g), low viscosity (1.93 cSt), and a reduced heating value (44.39 MJ/kg). In contrast, WCO biodiesel oil exhibited strong ester characteristics, contributing to improved combustion and stability. Blending WRPO with WCO biodiesel oil at a 50:50 ratio (P50:B50 blend) enhanced fuel properties, including a density of 895 kg/m3, reduced viscosity (3.28 cSt), and a lower acid value (0.26 mg KOH/g), along with an increased heating value of 45.60 MJ/kg—approaching that of conventional diesel. Engine testing showed improved torque and reduced brake-specific fuel consumption (BSFC) compared to pure WRPO. Emission analysis revealed reductions in CO (18.5 %), HC (23.7 %), and smoke opacity (16.2 %), while NOx emissions remained below diesel levels due to the lower combustion temperature of WRPO. These results suggest that the P50:B50 blend effectively addresses the drawbacks of WRPO, offering a promising, sustainable alternative to conventional diesel through improved performance, reduced emissions, and waste-to-energy valorization. © 2025 The Authors