## 2 Materials and Methods  
The turbocharged SI engine considered for the study powers a two-seater vehicle weighting 720 kg. It outputs 40 kW peak power, which ensures a 135 km/h top speed. The overall concept feasibility was previously validated with respect to driving range and peak power operation [28]. A rough estimate of the range was found to be around 100 km with a 30 L H\({}_{2}\) container at 700 bar (fitted alongside the 22 L OEM gasoline tank), which is comparable to the 130 km-range figure of the electric version of the vehicle [29]. An even higher range of around 170 km would be possible if the gasoline tank were substituted with H\({}_{2}\) bottles [30] (of course, if all aspects related to gas line routing and safety were mitigated successfully). The full-load condition was chosen as the starting point for the analysis. Urban and highway use was also considered by calculating equivalent engine output at 30, 50, 90, and 130 km/h constant vehicle speed. The passenger car features an automated manual gearbox, and a gear shift strategy of around 3000 rpm was taken as representative. Engine speed and load were calculated for each of the four vehicle velocity points. Given the purpose of the passenger car, urban driving is most likely, and even if the 2480, 3130, and 2940 rpm values used for 30, 50, and 90 km/h in 3 rd, 4 th, and 5 th gear, respectively [30], seem elevated, they fit the aforementioned gear shift strategy designed to ensure acceptable vehicle dynamics with contained engine torque. Figure 1 shows an overall layout of the power unit, with highlighted components and gas flow paths, including EGR. Table 1 shows its main specifications. The gas injectors are shown to be located upstream in the intake runners (only for illustration purposes), but the actual location in the simulations was considered close to the intake port. A 0D/1D model was built using OEM data and measurements performed on a disassembled unit. The overall concept is that components are represented as combinations of simple volumes (e.g., series of pipes, splits, and so on) [31]. Figure 2 illustrates the overall model layout and the control-oriented approach, for which injection, ignition, wastegate, and EGR valve actuation was performed by PID controllers. Most model specifics are available in [28,30]. Basically, the control logic acts on the throttle during partial-load operation (while keeping a compressor pressure ratio of 1) and on the wastegate when boosting is required (with the throttle wide open). A compressor surge limit was implemented in the PID-turbo component, and the PID-spark element featured a target of 9 deg aTDC for the 50% MFB combustion-phasing parameter. A reduction in the spark advance was implemented as a limit in the PID controller when knocking was predicted. \begin{table}
\begin{tabular}{c c} \hline Displacement & 599 cm\({}^{3}\) \\ Number of cylinders & 3 \\ Rated power & 40 kW @ 5250 rpm \\ Rated torque & 80 Nm @ 2000–4400 rpm \\ Bore \(\times\) Stroke & 63.5 mm \(\times\) 63.0 mm \\ Connecting rod length & 114 mm \\ Compression ratio & 9.5:1 \\ Number of valves & 2 per cylinder \\ Intake valve opening/closure & 363/164 deg DTDC \\ Exhaust valve opening/closure & 157/349 deg a/bTDC \\ Fuel system & Port fuel injection at 3.5 bar for gasoline and 5 bar for gas H\({}_{2}\) \\ Ignition & Inductive discharge, 2 spark plugs per cylinder \\ \hline \end{tabular}
\end{table} 
Table 1: Engine specifications. Figure 1: Illustration of the engine setup considered for simulation and the added EGR components in the LP configuration. Compared to previous versions of the model [28; 30], the recirculation circuit was added (including routing components and valve), as well as a heat exchanger; this was chosen so as to minimize the negative effects of charge heating. Special attention was paid to modeling as accurately as possible the geometry of the intercooler and EGR cooling module so as to obtain results that included the related thermal effects as much as possible.