## 2 Methodologies
### Investigation Programme
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Operating Condition** & **Control Variables** & **Tests** & **Control Variables (LP EGR** \\
**1p = n \(\times\) bmep** & **(Fixed in Each Test)** & **and VNT Control)** \\ \hline \multirow{6}{*}{No.1 = 1500 \(\times\) 2} & \multicolumn{3}{c}{Rel.AFR = 3.01-TV pos. 1} \\  & Relative air-fuel ratio & Rel.AFR = 2.90 1-TV pos. 1 2,3 & LP EGR valve opening \\  & Exhaust throttle valve position & Rel.AFR = 2.77-TV pos. 1,2 & VNT opening degree \\  & Rel.AFR = 2.62-TV pos. 1,2 & \\ \cline{2-3}  & \multicolumn{3}{c}{\(\text{A}_{\text{VNT}}\) = 1.4\(\%\)-9.5\(\%\)-16.5\(\%\)} \\  & \multicolumn{3}{c}{\(\text{SOI}_{\text{pilot}}\) = 20.1 CAD BTDC, \(\text{SOI}_{\text{pre}}\) = 8.0 CAD BTDC, \(\text{SOI}_{\text{main}}\) = 1.3 CAD ATDC, \(\text{Q}_{\text{pilot}}\) = \(\text{Q}_{\text{pre}}\) = 1 mm\({}^{3}\)/stroke, \(\text{p}_{\text{rail}}\) = 370 bar} \\ \hline \multirow{6}{*}{No.2 = 2000 \(\times\) 5} & Relative air-fuel ratio & Rel.AFR = 1.94-TV pos. 1 2,3 & LP EGR valve opening \\  & Exhaust throttle valve position & Rel.AFR = 1.80 1-TV pos. 1 2,3 & VNT opening degree \\  & Rel.AFR = 1.67-TV pos. 1,2 & \\ \cline{2-3}  & \multicolumn{3}{c}{\(\text{A}_{\text{VNT}}\) = 7.6\(\%\)-14.0\(\%\)-17.0\(\%\)} \\  & \multicolumn{3}{c}{\(\text{SOI}_{\text{pilot}}\) = 25.1 CAD BTDC, \(\text{SOI}_{\text{pre}}\) = 10.7 CAD BTDC, \(\text{SOI}_{\text{main}}\) = 1.1 CAD} \\  & ATDC, \(\text{Q}_{\text{pilot}}\) = \(\text{Q}_{\text{pro}}\) = 1 mm\({}^{3}\)/stroke, \(\text{p}_{\text{rail}}\) = 588 bar \\ \hline \multirow{6}{*}{No.3 = 2500 \(\times\) 8} & \multicolumn{3}{c}{Rel.AFR = 1.60-Intake press. = 1.48} \\  & Relative air-fuel ratio & bar-TV pos. 1 2,3 & bar-TV pos. 1 2,3 \\ \cline{1-1}  & Exhaust throttle valve position & Rel.AFR = 1.60-Intake press. = 1.52 & LP EGR valve opening \\ \cline{1-1}  & \multicolumn{3}{c}{\(\text{1}\),1.57 bar-TV pos. 0,1 1} \\ \cline{1-1}  & Intake pressure & Rel.AFR = 1.47-Intake press. = 1.52 & \\ \cline{1-1}  & \multicolumn{3}{c}{\(\text{SOI}_{\text{pilot}}\) = 31.6 CAD BTDC, \(\text{SOI}_{\text{pilot}}\) = 14.4 CAD BTDC, \(\text{SOI}_{\text{main}}\) = 0.1 CAD ATDC, \(\text{Q}_{\text{pilot}}\) = \(\text{Q}_{\text{pre}}\) = 1 mm\({}^{3}\)/stroke, \(\text{p}_{\text{rail}}\) = 812 bar} \\ \hline \hline \end{tabular} \({}^{1}\) Standard values.  
\end{table} 
Table 5: Schedule of experimental activities for test Set 2. Test Set 4 was again related to rail pressure control, applying the same levels of the previous step to the standard condition. Tables 7 and 8 show the average values of the EGR rate, charge dilution index, intake quantities and VNT opening degree in the three operating conditions. As a matter of fact, slight variations of parameters were observed but they were generally included in the range of measurement uncertainties. Increasing the fuel pressure injection led to a decrease in fuel consumption, affecting the relative air fuel ratio; to keep this variable to its target level, a reduction in air mass flow rate was requested, obtained through an increase of HP EGR valve opening. This behaviour was generally confirmed in test modes but effects on parameters listed in Tables 7 and 8 were negligible. A higher influence was shown by NOx and soot emissions, fuel consumption and combustion parameters, as will be discussed in the following section.