*3.2. Internal Combustion Engines*

The powertrain model elaborated in this work used the quasi-static approach for the simulation of the internal combustion engines. The engine characteristics were obtained experimentally in steady operating regimes and then implemented in the form of lookup tables. During simulations, the characteristics were interpolated using dynamic values of the engine rpm and the torque command calculated using the model. The required characteristics of the engines were obtained via laboratory dynamometer tests. In those tests, several parameters were measured and logged, namely the shaft speed, shaft torque, and fuel consumption, which were then employed for modeling purposes.

Figure 3 shows the BSFC map of the diesel engine and its maximum torque curve denoted as "Max. trq." The main performance parameters of this engine confirmed using the tests were as follows: rated power 331 kW (at 1900 rpm) and 1985 Nm maximum torque (at 1300 rpm).

**Figure 3.** Brake-specific fuel consumption (BSFC) map of the diesel engine.

Similar maps were built from the dynamometer test data for the gas engines (Figure 4). The main performance parameters of these engines were also confirmed: gas Otto's cycle—rated power 326 kW (1900 rpm), maximum torque 1900 Nm (1300 rpm); gas Miller's cycle—rated power 384 kW (1900 rpm), maximum torque 1950 Nm (1400 rpm).

**Figure 4.** Brake-specific fuel consumption maps of the developed gas engines: (**a**) Otto's cycle and (**b**) Miller's cycle.

One can notice that the engine with the Otto's cycle has a steeper gradient for the BSFC than that of the Miller-cycle engine, especially at low loads. This suggests that a wider part of the engine map should be excluded (if possible) from operating regimes through hybridization in the case of the Otto engine. It can also be seen that the Miller-cycle engine has an apparent torque dip at low shaft angular speeds, which should be compensated for using the additional torque of the electric machine (i.e., the "torque boost" feature).
