## 2 Methodologies
### Investigation Programme
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Operating Condition** & & & & & & \\
**ID = n \(\times\) bmep** & & & & & \\
**[rpm \(\times\) bar]** & & & & & & \\ \hline \multirow{6}{*}{No.1 = 1500 \(\times\) 2} & 3.3 & 0 & 0 & 1.134 & 59.1 & 27.9 \\ \cline{2-6}  & 3.2 & 15.8 & 0.191 & 1.118 & 65.9 & 31.5 \\ \cline{2-6}  & 3.0 & 18.8 & 0.236 & 1.105 & 64.2 & 34.2 \\ \cline{2-6}  & 2.9 \({}^{1}\) & 22.1 & 0.291 & 1.092 & 62.1 & 37.5 \\ \cline{2-6}  & 2.7 & 25.7 & 0.354 & 1.079 & 61.0 & 41.1 \\ \cline{2-6}  & \multicolumn{2}{c}{SOT\({}_{\mathrm{plot}}\) = 20.1 CAD BTDC, \(\mathrm{SO_{pre}}\) = 8.0 CAD BTDC, \(\mathrm{SO_{main}}\) = 1.3 CAD ATDC, \(\mathrm{Q_{plot}}\) = \(\mathrm{Q_{pre}}\) = 1 mm\({}^{3}\)/stroke, \(\mathrm{P_{tail}}\) = 370 bar, \(\mathrm{A_{VNT}}\) = 1.4\%} \\ \hline \hline \multirow{6}{*}{No.2 = 2000 \(\times\) 5} & 2.5 & 0 & 1.513 & 106.5 & 25.2 \\ \cline{2-6}  & 2.2 & 13.4 & 0.160 & 1.433 & 105.0 & 31.4 \\ \cline{2-6}  & 2.0 & 17.8 & 0.224 & 1.390 & 101.1 & 36.6 \\ \cline{2-6}  & 1.8 \({}^{1}\) & 22.8 & 0.306 & 1.341 & 95.7 & 43.6 \\ \cline{2-6}  & 1.6 & 27.6 & 0.396 & 1.299 & 92.2 & 51.6 \\ \cline{2-6}  & \multicolumn{2}{c}{SOT\({}_{\mathrm{plot}}\) = 25.1 CAD BTDC, \(\mathrm{SO_{pre}}\) = 10.7 CAD BTDC, \(\mathrm{SO_{main}}\) = 1.1 CAD ATDC, \(\mathrm{Q_{plot}}\) = \(\mathrm{Q_{pre}}\) = 1 mm\({}^{3}\)/stroke, \(\mathrm{P_{tail}}\) = 588 bar, \(\mathrm{A_{VNT}}\) = 7.6\%} \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Schedule of experimental activities for test Set 1 and average values of operating parameters (operating conditions No.1 and 2). were actuated in the selected operating conditions. As already explained, the last two variables were referred to the open and closed-loop control schemes available for VNT management. Referring to the throttle valve at the exhaust end, position 1 allowed us to obtain a pressure level at the turbine exit corresponding to a regenerated diesel particulate filter. To increase the mass flow rate from the low-pressure EGR loop, more closed positions were actuated (2 and 3), while setting 0 corresponded to a reduction of pressure along the exhaust circuit. Therefore, in points No.1 and 2, relative AFR and TV position were selected for each test, where the first mode corresponded to the activation of the HP EGR loop (LP contribution = 0). Then, the LP EGR valve was increasingly opened. When the maximum contribution from the LP EGR circuit was obtained, VNT control was added, opening the device to reduce exhaust back pressure. As shown in Table 5, in point No.3, each test was characterised also by a constant value of intake pressure, while only LP EGR valve control allowed to modify engine behaviour. Processing of the wide experimental database collected in test Set 2, allowed to select proper engine modes, as discussed in Reference [20]. These modes were characterised by a significant reduction in NO\({}_{\text{X}}\) emissions, lower levels of fuel consumption, limited penalties in soot emissions and increased values of turbocharger speed, always referring to the standard Euro 5 configuration. Starting from the corresponding values of control variables, test Set 3 was then developed according to the levels presented in Table 6. Two series of tests were scheduled for each operating condition to apply rail pressure control, aiming at reducing soot emissions and analysing the influence of this quantity on engine outputs and combustion parameters.