## 2 Materials and Methods  
### Fuel  
During tests on a dynamometer bench at the Institute of Vehicles and Working Machinery, the engine was powered by two fuels. First, tests were carried out by powering the engine with diesel fuel as a basis for comparing the results obtained. Then, empirical tests were carried out by powering the engine with a second-generation biofuel, namely hydrotreated vegetable oil. Table 1 shows the key physical and chemical parameters of both fuels. These properties alone give rise to the hypothesis that HVO fuel could replace diesel if its physicochemical parameters were similar to those of diesel listed in Table 1.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Properties** & **Unit** & **Method** & **HVO** & **Diesel Fuel** \\ \hline Kinematic viscosity & \(\frac{\text{m}\text{m}^{2}}{\text{m}^{3}}\) & - & 2.646 & 2.969 \\ Density (at 15 \({}^{\circ}\)C) & \(\frac{\text{kg}}{\text{m}^{3}}\) & - & 778 & 830 \\ Dynamic viscosity & Pa-s & - & 2.06-10\({}^{-3}\) & 2.47-10\({}^{-3}\) \\ Cetane number & - & ASTM-D613 & 79.7 & 54.6 \\ Pour point & K & ISO3016 & 215 & 234 \\ Flash point & K & ISO2719 & 339 & 344 \\ Cold filter & K & EN 116 & 229 & 251 \\ Plugging point & Total aromatic & \% \(\
icefrac{{}}{{}^{\circ}}\)/\(\
icefrac{{}}{{}^{\circ}}\) & - & 0 & 23.1 \\ Polyaromatic & \% \(\
icefrac{{}}{{}^{\circ}}\)/\(\
icefrac{{}}{{}^{\circ}}\) & - & 0 & 3.0 \\ Monoaromatic & \% \(\
icefrac{{}}{{}^{\circ}}\)/\(\
icefrac{{}}{{}^{\circ}}\) & - & 0.50 & 20.1 \\ Flammability & K & - & 334 & 347 \\ Lower heating & \(\frac{\text{kg}}{\text{kg}}\) & - & 44.35-10\({}^{6}\) & 42.65-10\({}^{6}\) \\ Sulfur & \% m/m & - & 0.53 & 6.50 \\ Carbon & \% m/m & - & 85 & 85.67 \\ Oxygen & \% m/m & - & 0 & 0.61 \\ Hydrogen & \% m/m & - & 15 & 13.72 \\ Ash content & \% m/m & EN ISO 6245 & 0.002 & 0.014 \\ FAME & \% \(\
icefrac{{}}{{}^{\circ}}\)/\(\
icefrac{{}}{{}^{\circ}}\) & - & 0.05 & 5 \\ Approx. formula & \% \(\
icefrac{{}}{{}^{\circ}}\)/\(\
icefrac{{}}{{}^{\circ}}\) & - & C\({}_{13}\)H\({}_{28}\) & C\({}_{13}\)H\({}_{24}\)O\({}_{0.06}\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Selected properties of HVO and diesel oil [26; 27; 28; 29; 30].  
Hydrogenated vegetable oil fuel is a type of biofuel that is produced by hydrogenating vegetable oil to make a substitute for traditional petroleum fuels such as gasoline and diesel. The process is designed to change the chemical properties of vegetable oil to give it characteristics more similar to conventional fuel [8; 27; 31; 32; 33]. Hydrogenated fuel from vegetable oil can be used in internal combustion engines as an alternative to petroleum fuels. It is often considered an environmentally friendly option because vegetable oils are biodegradable and can be a renewable energy source, unlike petroleum fuels, which are a limited resource and generate greenhouse gas emissions [23; 24; 31; 32; 33]. An essential advantage of HVO fuel is its freezing point, which can be as high as 215 K [34; 35]. HVO fuel has a density similar to conventional diesel fuel, making it potentially suitable for direct use in existing diesel engines without modification. HVO fuel tends to have a low kinematic viscosity, which may affect its easier splashing of injectors in diesel engines. The heating value of HVO fuel is similar to that of diesel, which means it can provide a similar amount of energy when burned. HVO fuel is typically sulfur-free and contains far fewer other pollutants than diesel fuel, which can help reduce harmful emissions into the atmosphere [36; 37; 38]. One solution that will consider the environmental protection goal, while not requiring rapid reorganization of the operations of companies and ordinary households, is to use biofuel as a substitute for diesel fuel [39; 40]. Such a fuel is hydrotreated vegetable oil.