Assessing the rheological properties of waste cooking oil biodiesel for sustainable fuel application

Abstract The global search for sustainable and renewable energy alternatives has brought biodiesel into focus, particularly that produced from waste materials such as waste cooking oil (WCO). This study aims to assess the rheological properties of biodiesel derived from WCO to determine its feasibility as an alternative to conventional fossil diesel. Rheological behaviour, including viscosity, shear stress, and flow characteristics, plays a critical role in fuel injection, atomization, and combustion performance in engines. Therefore, a detailed analysis of these properties is essential for practical biodiesel applications. WCO was collected, filtered, and converted into biodiesel using a transesterification process. The resulting biodiesel was subjected to rheological analysis using a rotational rheometer across a range of temperatures (10°C to 60°C) and shear rates. The results were compared with those of conventional diesel to assess performance differences. The biodiesel demonstrated a temperature-dependent decrease in viscosity, indicating improved flow properties at higher temperatures. At lower temperatures, the biodiesel exhibited slightly non-Newtonian behaviour, whereas at temperatures above 40°C, it behaved as a Newtonian fluid, aligning with the behaviour of standard diesel fuels. Compared to conventional diesel, WCO biodiesel showed higher viscosity at lower temperatures, which may require consideration in cold climate applications. However, all rheological values remained within the acceptable range specified by international biodiesel standards (e.g., ASTM D6751 and EN 14214). These findings highlight the potential of WCO biodiesel as a sustainable, cost-effective fuel that contributes to waste.