This study examines the influence of diesel, bio-hydrogenated diesel (BHD), and biodiesel fuels on engine performance, combustion characteristics, and emissions across various engine loads. Fuel properties were evaluated according to American Society for Testing and Materials (ASTM) standards, with blends of BHD and biodiesel at different ratios analysed. Engine performance parameters, combustion characteristics, and emissions were measured using specialized instruments, including pressure sensors and gas analysers, across engine loads from 25% to 90%. Results demonstrate that BHD generally outperforms diesel and biodiesel in terms of brake specific fuel consumption (BSFC) and brake thermal efficiency (BTE), particularly at higher engine loads. Combustion characteristics such as the rate of heat release (RoHR) and in-cylinder pressure (ICP) varied with fuel type and load, indicating the importance of combustion stability and fuel-air mixing. Emissions analysis reveals trends in NOx, HC, CO, and smoke emissions, with BHD showing lower emissions compared to diesel and biodiesel under certain conditions. Additionally, exhaust particle distributions, analysed using an Engine Exhaust Particulate Sizer Spectrometer (EEPS), provided insights into particulate matter (PM) characteristics. Thermogravimetric analysis (TGA) reveals that soot from BHD and biodiesel is more readily oxidized and undergoes decomposition at lower temperatures compared to diesel fuel, contributing to our understanding of fuel effects on engine performance and emissions for future fuel formulation and combustion optimization strategies.