## 4 Conclusions  
This paper shows a theoretical comparison between a gasoline- and a hydrogen-fueled ICE equipped in an HEV; a set of simulations was performed in order to compare the two fuels in terms of both the engine efficiency and total energy consumption while keeping the maximum engine power constant. To obtain the same maximum power of the gasoline  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**ICE Configuration**} & \multirow{2}{*}{\begin{tabular}{c} **Total Energy** \\ **Consumption [k]** \\ \end{tabular} } & \begin{tabular}{c} **Energy Difference** \\ **Compared to** \\ **Gasoline** \\ **Hybrid [\%]** \\ \end{tabular} & \
\begin{tabular}{c} **Energy Difference** \\ **Compared to** \\ **Gasoline** \\ **Conventional [\%]** \\ \end{tabular} &
\begin{tabular}{c} **Total Fuel Mass** \\ **Consumption [kg]** \\ \end{tabular} \\ \hline gasoline & \(50\),\(731\) & \(+18.0\%\) & \(0\) & \(1.153\) \\ conventional & \(42\),\(930\) & \(0\) & \(-15.0\%\) & \(0.976\) \\ gasoline hybrid & \(38\),\(749\) & \(-9.7\%\) & \(-23.6\%\) & \(0.323\) \\ hydrogen TC & \(36\),\(430\) & \(-15.1\%\) & \(-28.2\%\) & \(0.304\) \\ hybrid & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 5: WLTC energy and fuel mass consumption comparison.  
fueled engine, the hydrogen engine must be supercharged, and the best solution proved to be a turbocharger driven by an exhaust gas turbine. The first comparison involves a conventional vehicle: the hydrogen turbocharged engine exhibited an average BTE 19.5% higher than that of the gasoline counterpart.  
A second comparison between the two fuels was performed considering the engine aboard an HEV that exploits, for each operating condition, the best engine efficiency. In this case, the hydrogen TC engine showed an average BTE 16.7% higher than that of the gasoline one. Finally, the WLTC driving cycle was considered in order to evaluate the total energy consumption of the engine equipped in the HEV and fueled either by gasoline or by hydrogen. In this case, the total energy consumption of the hydrogen-fueled engine (HEV) was 15.1% lower than that of the gasoline one (HEV) and 28.2% lower if compared with the gasoline engine aboard a conventional vehicle.  
An indicative mileage of 300 km was estimated for the hybrid hydrogen engine with a 150 L tank loaded at 300 bar pressure. The energy consumption reduction of 15.1% agrees with the above-mentioned literature results in which a range between 12% and 20% of gasoline equivalent fuel consumption reduction was reported between conventional fuel and hydrogen in HEVs.  
The higher engine efficiency when fueled with hydrogen compared with gasoline is mainly due to three reasons: the lean mixture composition (while gasoline, at full load and works with rich mixture), the better combustion phasing allowed by the higher knocking resistance and the shorter combustion duration due to the higher flame speed. In this work, the three mentioned advantages of hydrogen were quantified in terms of attainable engine efficiency increase and energy consumption reduction in HEVs.  
Our conclusion is that a hydrogen-fueled engine performs better than the gasoline counterpart in both conventional and hybrid vehicles; considering that hydrogen, under proper operating conditions, is a zero-emissions fuel, this represents an almost obligatory choice in the automotive field.  
This research received no external funding.  
Not applicable.  
The authors declare no conflict of interest.