## 3 Results and Discussion  
### Model Validation by Comparing Real-World Diesel Trucks with ICEV-CNG Truck Model (ICET-CNG)  
The most advanced and ecologically effective combustion-based drive technology is the CNG engine, which we therefore use as a benchmark. The first step on the way to our goal was to compare the simulation results of the ICET-CNG model with the real diesel consumption on the reference tours. Values from the literature were taken for the key consumption-determining parameters such as air and rolling resistance [50; 51] and then adjusted as dictated by the state of the art or by measurement results. Where ranges were given in the literature, we placed ourselves in the middle. For example, Ref. [52] gives a range of 0.49 to 0.77 for the air resistance of five-axle semi-trailer trucks. As this study provides very detailed information on the aerodynamics of heavy commercial vehicles but the data date back to 2012, the \(c_{\text{w}}\) value was initially set below the mid-point of 0.65.  
In contrast to air resistance, the values for the rolling resistance are quite uniform in the literature. We used 0.6% as the starting value in the model [52; 53].  
Some adjustments also had to be made to the characteristic curves of combustion engines due to technological developments. In Table 4 of [31], we achieved very good results with a maximum efficiency of 39% for the CNG engine. However, a few years ago, DAF launched a new, more economical generation of diesel trucks, the fuel consumption of which is stated to have been reduced by 10% [37; 54; 55; 56; 57]. Such fuel-efficient trucks were used on the long reference tour, whereas the short tour is still run with old-generation DAF XF trucks.  
The simulations were carried out on the basis of the vehicle data (Table 3), tour data (Table 2) and consumption-determining parameters (Table 9). This led to excellent agreement with the real consumption values for both tours (Figure 8). This is surprising given the high complexity of the traffic conditions described.  
The simulation determines the CNG consumption of an ICEV-CNG truck in kg per 100 km whereas the real-world consumption is for a diesel truck and is measured in liters per 100 km. The conversion was made using the empirically known fact that 10 L of diesel corresponds to 9 kg of CNG [58].  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**GHG Emission Factors** **(g CO\({}_{2}\)-Equiv./kWh)**} & \multicolumn{2}{c}{**2020/24**} & \multicolumn{2}{c}{**2030**} & \multicolumn{2}{c}{**2050**} \\ \cline{2-7}  & **Previous** & **Updated** & **Previous** & **Updated** & **Previous** & **Updated** \\ \hline Electricity \({}^{*}\) & 376 & 376 & 225 & 300 & 58 & 125 \\ \hline H\({}_{2}\) & 301 & 301 & 256 & 284 & 95 & 175 \\ \hline CNG & 230 & 230 & 195 & 195 & 76 & 126 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Updated GHG emission factors [47; 48; 49] (for previous estimates, see Section 3.4 of [31], \({}^{*}\) Germany).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{2}{c}{**Start Parameter Set**} & \multicolumn{2}{c}{**Adjusted Parameter Set**} \\ \cline{2-5}  & **Short Tour** & **Long Tour** & **Short Tour** & **Long Tour** \\ \hline Air resistance & 0.65 & 0.65 & 0.63 & 0.60 \\ \hline Rolling resistance & 0.60\% & 0.60\% & 0.58\% & 0.56\% \\ \hline CNG motor efficiency (max.) & 39\% & 39\% & 39\% & 42\% \\ \hline \hline \end{tabular}
\end{table}
Table 9: Parameter sets for the dominant variables influencing consumption.