## 4 Conclusions  
An investigation of the effects of alternative fuel blends (15% ethanol, 35% biodiesel, 50% diesel, E15B35D50, and 15% ethanol, 35% biodiesel, 50% F-T diesel, E15B35 FTD50) on the energy and exergy analysis and exhaust emissions was performed. This work extended the understanding regarding the energetic and exergetic performance of synthesized diesel-like fuels and biofuels (ethanol and biodiesel) as well as the exhaust emissions from the combustion of alternative fuels. The energy and the exergy efficiencies were found to be similar, around 26% and 24%, respectively, with a little difference. The energy efficiency and also exergy efficiency of the diesel engine fueled with F-T diesel and ethanol/biodiesel (E15B35 FTD50) was slightly lower than for the diesel fuel as a result of the inlet fuel energy and the higher fuel chemical exergy of the blend, respectively. The major cause of the inefficiency of the engine was the destroyed exergy caused by the irreversibilities of the system, especially by the combustion \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Engine** & **Operating** & **Fuel Type** & **Energy (\%)** & **Energy (\%)** & \\
**Characteristics** & **Conditions** & & **Efficiency (\%)** & **Efficiency (\%)** & \\ \hline \multirow{2}{*}{1-cylinder 4 stroke} & \multirow{2}{*}{1500 rpm} & Diesel & & \\  & & E15/B35/D50 & 26.2–26.6 & 24.4–24.9 & \(\eta_{\text{diesel}}>\eta_{\text{blends}}\) \\  & & E15/B35/FTD50 & & \(\psi_{\text{diesel}}>\psi_{\text{blends}}\) \\ \hline \hline \end{tabular}  
* D: diesel fuel, B: biodiesel fuel, E: ethanol fuel, FTD: Fischer-Tropsch diesel fuel.  
\end{table} 
Table 6: Summary of the energy and exergy results of this work. Figure 8: Energy flow (Sankey) diagrams on the left side and exergy flow (Grossman) diagrams on the right side showing the comparison of energy and exergy efficiencies of the engine fueled with (**a,b**) diesel; (**c,d**) E15B35D50; (**e,f**) E15B35 FTD50. process. The exergy losses from exhaust gases and from the sum of the other losses also contributed to a decrease in the efficiency of the engine. Besides, it could be concluded that the sustainability index of the diesel fuel was higher than for the blends. The combustion of the fuel blends containing the biofuels (ethanol and biodiesel) produced lower levels of exhaust emissions such as HC, NO, NH\({}_{3}\), and N\({}_{2}\)O compared to diesel fuel, however with a penalty on the CO emissions. Overall, the utilization of synthetic F-T diesel and biofuels such as ethanol and biodiesel can effectively mitigate the engine-out emissions, resulting in a similar efficiency of the engine. Thus, these alternative fuels that may be used without requiring modifications to the engine can also contribute to the reduction of fossil diesel utilization. These findings will be beneficial for biofuel and diesel hybrid electric vehicle synergies to achieve emission regulations by 2050. Besides, only limited literature evaluated the effects of the utilization of F-T diesel, ethanol, and biodiesel on the engine emissions without in-depth engine calibration. Furthermore, none included the light hydrocarbons speciation and unregulated emissions, such as NH\({}_{3}\) and formaldehyde. Due to the compatibility of advanced combustion strategies (i.e., RCCI and GCI) in hybrid electric vehicles, it is suggested that future research investigate the performance of ethanol and FT-diesel as well as higher chain alcohols (i.e., butanol and pentanol). Butanol and pentanol provide better miscibility as blended with FT-diesel. Additionally, investigation of advance combustion strategies of alternative fuels with aftertreatment systems can fasten hybridization. Conceptualization, F.A.T., O.D., J.M.H. and A.T.; methodology, F.A.T., O.D. and J.M.H. ; formal analysis, F.A.T., O.D. and R.L. ; investigation, F.A.T., O.D., R.L. and R.P. ; resources, A.T.; writing--original draft preparation, F.A.T. ; writing--review and editing, O.D., J.M.H., A.T., J.M. and S.A.B.V.d.M. ; supervision, A.T., J.M. and S.A.B.V.d.M.