## 2 Equipment, Methodology and Fuel  
A comparative study of engine performance was conducted using a compression ignition engine (AUDI, 1.9 TDI, 1z) controlled by an electronic control unit (ECU). Fuel was supplied to the engine using a BOSCH VP37 axial piston distributor type injection pump and two spring hole type nozzle injectors. Air was supplied using a turbocharger. The engine was equipped with an exhaust gas recirculation (EGR) system. Table 1 presents the key engine data. A diagram of the equipment used in the experimental research is presented in Figure 1. For the engine load, the brake torque \(M_{B}\) was measured using the KI-5543 load bench (accuracy of measurement = 1.2 Nm). Fuel consumption was determined using the SK-5000 scale (accuracy of measurement = 1.0 g) and a stopwatch. The intake air mass was measured using the BOSCH HFM 5 air mass meter (accuracy \(\leq\) 2%). For the fuel injection timing, the start of injection (SOI) was determined using VAG-COM diagnostic equipment connected to the ECU On-board diagnostics (OBD) connector. A needle lift sensor integrated in the fuel injector generated SOI information. The in-cylinder pressure was measured using a glow plug adapter with an AVL GH13P integrated piezo pressure sensor, with its sensitivity/linearity at 250 \({}^{\circ}\)C being 15.88 (pC/bar)/\(\pm\)0.11 (%Fast Cookoff Sensor (FCO)). The crankshaft position was determined using an A58M-F encoder (accuracy = 0.1758 crank angle degrees (CAD)). The 100 cycle in-cylinder pressure and CAD data were transmitted using an AVL DiSTEST DPM 800 oscilloscope and recorded using LabView Real software. The pressure in the engine intake manifold was measured using a Delta OHM HD 2304.0 and a TP704-2 BAI sensor (accuracy = \(\pm\)0.0002 MPa). A Type K thermocouple with an accuracy of \(\pm\)0.5% was used to measure the intake air and the exhaust gas temperature. The concentrations of various components (carbon dioxide (CO\({}_{2}\)), carbon monoxide (CO), hydrocarbons (HCs), nitrogen oxides (NO\({}_{x}\)) and the smoke absorption coefficient) in the exhaust gas were measured using an AVL DiCom 4000 gas analyzer and the opacimeter. The gas analyzer accuracies were as follows: 0.1% vol. for CO\({}_{2}\); 0.01% vol. for CO; 1 ppm for HC; 1 ppm for NO\({}_{x}\); and 0.01 m\({}^{-1}\) for smoke. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Displacement & 1986 cm\({}^{3}\) \\ Number of cylinders & 4 \\ Compression ratio & 19.5 \\ Piston diameter & 79.5 mm \\ Piston stroke & 95.5 mm \\ Power & 66 kW (4000 rpm) \\ Torque & 182 Nm (2000–2500 rpm) \\ Fuel injection & Direct \\ Pressure of the opening of the fuel injector & 190 bar \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The main parameters of the compression ignition engine. The experimental research was conducted at a constant engine speed of \(n=2000\) rpm and three different loads (\(M_{B}=45\) Nm, \(M_{B}=60\) Nm and \(M_{B}=90\) Nm), corresponding to a brake mean effective pressure (BMEP) of 0.3 MPa, 0.4 MPa and 0.6 MPa, respectively. Engines operate in this mode when cars run at a speed of \(\sim\)50-100 km/h. Tests were also performed with EGR off and on. When conducting a test with EGR on, the ECU controlled the EGR valve; the EGR flow was set for assessing the intake air mass. At different engine loads (BMEP = 0.3 MPa, 0.4 MPa and 0.6 MPa), the EGR coefficient was \(k_{EGR}\) = 0.27, 0.26 and 0.19, respectively. Numerical analysis of the combustion process was performed using the AVL BOOST software with the BURN utility. The rate of heat release (ROHR) was calculated during combustion according to cylinder pressure traces measured during the experiment, the fuel and air consumption, fuel properties and engine data, using the laws of thermodynamics and mechanics. The start of combustion (SOC), temperature, rise in temperature and rise in pressure in the cylinder were determined.