## 4 Results and Discussion
### Numerical Results
Generally, swirl is defined as an organized rotation of charge around the axis of the cylinder. The swirl grows based on initial angular momentum through the intake flow into the cylinder. The air motion inside the cylinder affects the combustion process. Increasing the swirl density causes an acceleration of the mixing process due to increased air velocity and provides conditions for a flammable mixture at the ignition point. As shown in Figure 17, the numerical results of thermal efficiency were enhanced by adding biodiesel and AL2O3 nanoparticles to increase the engine performance, where the best engine performance was obtained with the D80B20N150 mixture. The nanoparticles enhance the combustion process and increase the surface area and efficiency compared to pure diesel fuel by 2.8% at the highest load capacity of 90%. A decrease in thermal efficiency was observed when mixing diesel fuel with biodiesel, by 4.8% D80B20. There is also an improvement in thermal efficiency by adding nanoparticles. Therefore, adding aluminum nanoparticles reduces the ignition period and fuel evaporation time. In addition, it improves the fuel and combustion properties compared to conventional fuel. Nanoparticles improve the mixing of air with fuel as they have a larger surface area, which contributes to improving the chemical reaction. Figure 16: Contours of velocity distribution at different crank angles of D80B20N150 at a load of 200 Nm. Figure 18 shows the results of CO\({}_{2}\) emissions at an engine speed of 1150 rpm and a load of 200 Nm for all fuel samples; the CO\({}_{2}\) mass fraction for D80B20 was higher than that for D100 by 4.41%. When adding the nanomaterial for D80B20N50, there was an increase in the CO\({}_{2}\) mass fraction by 8.45%. As for increasing the nanomaterial D80B20N100, the increase in the CO\({}_{2}\) mass fraction was higher than that for pure diesel, as it reached 14.47%. Finally, when increasing the nanomaterial D80B20N150, there was an increase in the CO\({}_{2}\) mass fraction compared to that for diesel fuel, as it reached the rate of 18.7%, and this increase is considered a good factor. Also, the results were in good agreement with the experimental results. While Figures 19-21 reported the contours of the CO\({}_{2}\) mass fraction of different fuel blends at engine speeds of 1400, 1600, and 1800 rpm with an engine load of 200 Nm, respectively, Table 7 presents the variation of increase in the percentages of the CO\({}_{2}\) mass fraction for all fuel samples relative to pure diesel D100. Figure 22 presents the numerical results of CO\({}_{2}\) emissions with the engine speed for all additives. Figure 17: The variation of the Numerical BTE with the engine load for fuel blend samples. Figure 18: Contours of CO\({}_{2}\) mass fraction of different fuel blends at a load of 200 Nm and speed of 1150 rpm. Figure 19: Contours of CO\({}_{2}\) mass fraction of different fuel blends at a load of 200 Nm and speed of 1400 rpm. Figure 11:0 Contours of CO\({}_{2}\) mass fraction of different fuel blends at a load of 200 Nm and speed of 1600 rpm. Figure 11:1 Contours of CO\({}_{2}\) mass fraction of different fuel blends at a load of 200 Nm and speed of 1800 rpm. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Engine Speed**} \\ \hline Fuel samples & 1150 rpm & 1400 rpm & 1600 rpm & 1800 rpm \\ \hline D80B20 & 4.41\% & 4.28\% & 2.53\% & 2.6\% \\ \hline D80B20N50 & 8.45\% & 8.21\% & 3.75\% & 5.1\% \\ \hline D80B20N100 & 14.47\% & 10.6\% & 6.1\% & 7.4\% \\ \hline D80B20N150 & 18.7\% & 12.8\% & 8.33\% & 9.67\% \\ \hline \end{tabular}
\end{table} 
Table 7: Variation of CO\({}_{2}\) mass friction percentages for all fuel samples relative to pure diesel. Figure 22: Numerical results of CO\({}_{2}\) emissions with engine speed for all additives. Figure 23 shows the results of NOx emissions at an engine speed of 1150 rpm and load of 200 Nm for all fuel samples; the mass fraction of NOx for D80B20 was higher than that for D100 by 5.7%.