## 3 Results and Discussion
The mean engine BTE, in this case, was evaluated as the average value over all the points lying in the BEP. Figure 7 shows the BTE maps of hydrogen-fueled engines in both TC and VSC configuration with the BEP curves. The mean BTE value of the hydrogen-fueled engine, equipped in an HEV is evaluated by averaging the BTE values lying on the BEP curves. Table 3 shows, for all the three engine configurations, the power and BTE values of all the points lying on the BEP. Figure 6: The gasoline-engine BTE map with the BEP in green. Figure 7: The hydrogen-engine BTE map with the BEP in green. Table 4 shows the average values extracted from Table 3, which are the mean BTE of a gasoline- or hydrogen-fueled ICE when equipped in an HEV. Some important considerations can be drawn: The ICE hybridization brings great benefits to the mean BTE in both gasoline (+15.9%) and hydrogen (+8.0% and +13.3%) configurations. TC remains, also in HEV, a better alternative than VCSC. Finally, the TC hydrogen ICE has a higher mean BTE than the gasoline hybridized engine in both the conventional and hybridized configurations with increases of +3.1% and +16.7%, respectively. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**HEV ICE Configuration** & **Mean BTE** & \
\begin{tabular}{c} **\% Increase Compared to** \\ **Gasoline Hybrid** \\ \end{tabular} &
\begin{tabular}{c} **\% Increase Compared to** \\ **Conventional** \\ \end{tabular} \\ \hline gasoline & 0.245 & 0 & 15.9\% \\ hydrogen VCSC & 0.266 & 8.6\% & 8.0\% \\ hydrogen TC & 0.286 & 16.7\% & 13.3\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The mean BTE of the three engine configurations in an HEV. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Power [kW]** & **BTE Gasoline** & \ \begin{tabular}{c} **Power [kW] SC** \\ **Hydrogen** \\ \end{tabular}  & **BTE SC Hydrogen** & \begin{tabular}{c} **Power [kW] TC** \\ **Hydrogen** \\ \end{tabular}  & **BTE TC** \\
3.9 & 0.182 & 4.2 & 0.226 & 3.6 & 0.212 \\
4.6  
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In order to test the three hybridized engines (gasoline, VCSC and TC hydrogen) in a more realistic situation, they were implemented in the WLTC driving cycle as described above. Table 5 resumes the findings, in terms of the total energy consumed in the WLTC, of both gasoline- and hydrogen-fueled engines. All the hybrid configurations show a strong reduction of energy consumption compared to the conventional gasoline engine, from the \(-15\%\) of the hybrid gasoline to the \(-23.6\%\) of the VCSC hybrid and finally to the \(-28.2\%\) of the TC hybrid, and this confirms the effectiveness of the hybrid technology in increasing the vehicle efficiency by exploiting the engine best efficiency operating points and by recovering the vehicle kinetic energy. Table 5 highlights the efficiency increases specifically due to the use of hydrogen in a hybrid vehicle with respect to gasoline (third column). The hydrogen VCSC hybrid engine shows a total energy consumption that is \(9.7\%\) lower than the gasoline hybrid, and the hydrogen TC hybrid engine is \(15.1\%\) lower than the gasoline hybrid confirming the already discussed mean efficiency increases reported in Table 4.  
The total fuel mass consumption of hydrogen (in both TC and VCSC configurations) was lower than one third that of gasoline, and the main reason is the lower heating value of hydrogen that is three times that of gasoline. In any case, a vehicle mileage evaluation can be made. The energy consumption reduction of \(15.1\%\) agrees well with the above-mentioned literature results [9; 10; 11; 12; 13; 14] in which a range between \(12\%\) and \(20\%\) of gasoline equivalent fuel consumption reduction has been reported between conventional fuel and hydrogen in HEV.