Biodiesel offers many advantages, including the following: (i) a 10 to 12% oxygen content by mass in its molecular structure, improving combustion efficiency and reducing emissions of CO, unburned hydrocarbons, and smoke; (ii) it reduces net CO\({}_{2}\) emissions by 78% over its life cycle compared to diesel fuel; (iii) it is biodegradable and non-toxic, protecting the environment; (iv) it has a higher ignition temperature and cetane number than diesel fuel; and (v) it improves lubricity, leading to the longer life of engine components [8; 9]. Overall, biodiesel is a sustainable and environmentally friendly alternative for our energy needs [8; 10]. Because animal fats include a large amount of saturated fatty acids, the biodiesel made from them have a greater melting point than those made from vegetable oil, making them unsuitable for diesel engine fuel. Nevertheless, biodiesel made from animal fats have a larger cetane number and calorific value than those made from vegetable oils, and they can be utilized in boilers to generate heat in their original form [11]. Another advantage concerns the fluidity of biodiesel at low temperatures [12; 13]. While biodiesel applications offer many benefits, there are also significant challenges, such as competition with the food industry, lower energy content and volatility, and higher viscosity and NOx emissions compared to diesel fuel [14]. It should be noted that growing biofuel crops rather than food crops, as the demand for biodiesel rises, reduces the land availability for cultivating the basic food supply. Therefore, increased crop use for biodiesel may have an impact on international agricultural markets, which would further affect food access and affordability worldwide [15]. Also, the biodiesel produced from oils, no matter if it is neat vegetable oil or animal fat, is usually more expensive than diesel fuel. Therefore, the high cost of biodiesel is the major obstacle to its commercialization [16]. Fuel atomization and combustion in diesel engines, which take place at high pressures and temperatures as well as derived thermodynamic forces, are significantly influenced by the density, specific gravity, and viscosity of the fuel [17; 18; 19]. Density is the mass of a unit volume of fuel; it is a useful indicator of the composition and operational characteristics of diesel fuel, such as ignitability, power, economy, and low-temperature flow characteristics. Density depends on the type of hydrocarbon composing the fuel and the number of carbons in the tramp oil. A report from the National Renewable Energy Laboratory (NREL), published in 2024, investigated the properties of high-level biomass-derived biodiesel with renewable diesel (RD) and petroleum diesel. The study measured various characteristics, including flash point, cloud point, cetane number, surface tension, density, kinematic viscosity, distillation curve, lower heating value, water content, water solubility, lubricity, and oxidation stability across a broad temperature range. The results indicated that certain properties, such as density and viscosity, may limit the ability to blend high concentrations of biomass-derived biodiesel with diesel fuels [20]. Moreover, the higher biodiesel density than diesel fuel may increase blend density and cause a distinct spray pattern and fuel atomization. The increased density of biodiesel can influence combustion time and pressure within the cylinder. Biodiesel releases energy more slowly than diesel, potentially delaying combustion. This could impact engine performance [21]. In addition, the specific gravity of a fuel is proportional to its energy content. In general, biodiesel will produce less energy for the same volume as regular diesel since it has a lower energy density. As a result, when using biodiesel at higher quantities, power output is reduced. Therefore, density and specific gravity are important parameters of fuels, which, together with cetane number and calorific value, are related to fuel impurities and viscosity.