## 2 Experimental Details  
The investigation was performed on a naturally aspirated, four-stroke tractor diesel engine UTB 2404055, which develops 48 kW at 2400 rpm constant speed. The engine specifications are presented in Table 1.  
The engine was installed in a test cell provided with the corresponding instrumentation for experimental investigation (Figure 1). The test bench was equipped with an AVL Alpha 160 eddy current dynamometer which accurately measures the engine instant torque and speed. The unit under test is monitored and controlled by the AVL EMCON 400. The SCHLUMBERER Fluxi 2000/TZ volumetric flow meter was used to measure the engine air consumption. The AVL Dynamic Fuel Meter 733S and AVL Fuel Temperature Controller 753C were used to measure the engine fuel consumption. The HORIBA Mexa 7170D gas analyser was used to measure the exhaust emissions of CO\({}_{2}\), CO, NO\({}_{\text{x}}\) and THC and to calculate the relative air-fuel ratio, while the AVL 415S measured the exhaust smoke expressed as Filter Smoke Number (FSN). The temperature and pressure of the exhaust gases, cooling water, intake air, oil as well as the atmospheric temperature and pressure were measured with appropriate devices through the signal conditioning system AVL FEM BOX and recorded by the AVL Puma Open v1.4 equipment. The data acquisition system for pressure diagrams consisted of an AVL 365C crank angle encoder and two AVL GM12D piezoelectric pressure transducers which were mounted in different cylinders and connected to the AVL 3066A02 charge amplifiers. The injector needle lift was recorded for one cylinder using a proximity sensor incorporated in a Perkins-Lucas injector. The AVL 3066A01 charge amplifier and AVL QL21D transducer equipped the high-pressure line of this injector. The fuel pressure measurement system at the injection pump consisted of an AVL 3009 A03 charge amplifier and an AVL 31 DP pressure transducer. An AVL IndiSet 620 data acquisition module recorded high-speed variation parameters using the AVL Indicom 1.6 software. In this work, the experimental data were collected for engine maximum brake torque-R1 (full load, 1400 rpm) and maximum brake power-R2 (full load, 2400 rpm) conditions when fuelling was successively made with diesel fuel and biodiesel B20. For every operating point, at least 3 tests were performed, each of them consisting in the registration of 200 consecutive cycles recorded cycle by cycle, an average cycle and statistical data. The relative deviations of the in-cylinder pressure variation comparative to the mean values were below 3%. The oil temperature stayed within 90 \(\pm\) 5 \({}^{\circ}\)C throughout the experiments. This was done using a heat exchanger equipped with two OMRON E5 CN temperature controllers and electrovalves. The temperature of the engine cooling water was maintained between 70 and 75 \({}^{\circ}\)C. The experimental data which were averaged have been considered as the basis for the calibration of the simulation model. Table 2 shows the measuring accuracy values for the main equipment used in this study. It is well known that carbon dioxide (CO\({}_{2}\)) is one of the harmful emissions of piston engines with a massive influence on the greenhouse effect, which induces the global warming phenomenon. To combat this undesirable phenomenon, continuously reducing carbon dioxide emissions must be promoted. One way to achieve this important goal is by using biofuels. Currently, commercial diesel fuel in the European Union has a content of 7% _v/v_ biodiesel (B7). The slow increase in the biofuel percentage allows the technological development of motor vehicles, the aim being to use high percentages of biofuel in the future to further reduce CO\({}_{2}\) emissions. For this reason, biodiesel B20 was considered important in this study, representing a potentially viable solution for the next future as it has only 20% volumetric fraction rapeseed biodiesel in its composition. In Romania, large rapeseed crops are cultivated.