## 4 Results and Discussion
The minimum values are obtained for the TR1 shape with reductions of 43.8% for diesel fuel and 33.2% for B20 on R1. For the other operating condition R2, the Soot reduction with the TR1 shape relative to the TH is 63% for diesel fuel and, respectively, 47.1% for B20. The ROI shapes, which concentrate a large amount of fuel injected up to the ignition time, enhance the mixing process and promote faster burning rates, which lead to higher NO\({}_{x}\) and lower Soot emissions. For both fuels, the maximum Soot values are obtained with the TH shape. Similar results on Soot emissions for diesel fuel usage have been reported in [9; 10; 13; 15; 22]. Nevertheless, some different results were presented in [7], where, for increased values of injection rate at the beginning of the injection process on certain boot shapes, higher Soot emissions were disclosed. As previously noted, the premixed combustion phase significantly influences the NO\({}_{x}\) and Soot emissions generation process. In this sense, a final part of this study was dedicated to the link existing between the amount of fuel injected in the initial stage of combustion and the values of pollutant emissions. For such analysis, the connection existing between the surface area under the ROI shapes (between the SOI\(-\) and MFB10% events) and the magnitude of NO\({}_{x}\) and Soot emission values was evaluated. The calculated values of surface area are presented in Table 6 for each ROI shape. The BO1, RT and TR1 shapes presented relative to the TH reference shape higher values of this surface area with average increases for both fuels of 25.8%, 24% and 19.2% on the R1 operating condition and, respectively, of 28.1%, 25.7% and 26.5% for the R2 test condition. Figure 13: Nitrogen oxides (NO\({}_{x}\)) variation by different shapes of ROI. Figure 15 shows the variations of NO\({}_{\rm x}\) and Soot emissions versus this surface area of injected fuel amount during the initial combustion stage. The correlation which can be detected is practically linear for both engine operating conditions and both fuels. An increase of 53% in the injection area for diesel fuel on R1 (from 3.6 to 5.5) is leading to an increase of 76% in NO\({}_{\rm x}\) on the trendline. A similar trend is registered for B20 too, but with a smaller increase of 50%. The Soot variation is however reversed, its decrease being of 24% for diesel fuel and 16% for B20 on the trendline, over the same range of the injection area. In the case of R2, the correlation remains linear, but it presents some differences existing between diesel fuel and biodiesel B20 mostly for NO\({}_{\rm x}\). The slopes of linear correlation for NO\({}_{\rm x}\) seem to have the same values for both fuels, but on B20, superior absolute values are registered. An increase of 57% of the injection area (from 3.9 to 6.2) is leading to a rise of 138% in NO\({}_{\rm x}\) emissions on the trendline for diesel fuel. On the same domain of the injection area, the average growth of NO\({}_{\rm x}\) emissions is smaller for B20, being around 86%. The Soot variation remains quasi similar for both fuels with a dropping on the trendline by 43% for diesel fuel and, respectively, 21% for B20. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**ROI Shape**} & \multicolumn{2}{c}{**R1 (Full Load, 1400 rpm)**} & \multicolumn{2}{c}{**R2 (Full Load, 2400 rpm)**} \\  & **SOI-MFB10\% Surface [-]** & **SOI-MFB10\% Surface [-]** \\ \cline{2-5}  & **D100** & **B20** & **D100** & **B20** \\ \hline TH & 4.39 & 4.22 & 4.76 & 4.90 \\ IT & 4.46 & 4.40 & 5.20 & 5.05 \\ RT & 5.50 & 5.30 & 6.06 & 6.06 \\ TR1 & 5.16 & 5.10 & 6.14 & 6.07 \\ TR2 & 4.81 & 4.63 & 5.61 & 5.15 \\ TR3 & 4.20 & 4.06 & 4.70 & 4.49 \\ BO1 & 5.37 & 5.32 & 6.18 & 6.18 \\ BO2 & 3.59 & 3.52 & 3.94 & 4.02 \\ \hline \end{tabular}
\end{table} 
Table 6: The surface area under the ROI shapes calculated between the SOI and MFB10% events. Figure 14: Soot variation by different shapes of ROI.