Particulate matter characteristics and emissions of waste- and bio-derived fuels in diesel engine applications

This study evaluates the performance, emissions, and particulate matter characteristics of alternative diesel fuels derived from waste plastic oil, palm oil-based biodiesel, and bio-hydrogenated diesel, compared with conventional diesel. The experiments were conducted using a single-cylinder diesel engine operated at 1500 rpm under four engine load conditions (25 %, 50 %, 75 %, and 90 %). Conventional diesel consistently demonstrates the highest thermal efficiency and lowest brake-specific fuel consumption, particularly at the 75 % load. In contrast, bio-hydrogenated diesel achieves the greatest nitrogen oxide reduction, with 89.7 % lower emissions compared with diesel at the highest load. Palm biodiesel shows the lowest hydrocarbon and smoke emissions, especially at the highest load, reducing smoke by over 46 % compared with diesel. Particulate matter analysis revealed that biodiesel produces high concentrations of nucleation-mode particles at a low load, while diesel and waste plastic oil generate larger accumulation-mode particles at the highest load. Thermal analysis indicated that particulate matter from biodiesel begins oxidation at lower temperatures than that from diesel and waste plastic oil, reflecting enhanced reactivity due to a higher oxygen content. Notably, particulate matter from waste plastic oil retains approximately 10 % of its mass after oxidation, suggesting potential challenges for emission control. Overall, while conventional diesel retains performance advantages, each alternative fuel offers specific environmental benefits. The findings support the potential of waste- and bio-derived fuels to reduce harmful emissions and particulate matter, although further optimisation of fuel formulation and after-treatment strategies is needed to enhance their practical viability for sustainable transportation applications.