## 3 Discussion of the Results  
Figure 2a shows the vehicle speed during the WLTC superimposed over the engine torque provided by the engine to reach it. The driving cycle is composed of four speed phases, from low to extra-high speed, which will be taken as reference to conduct the analysis of the results along with the total cumulative result of mass-based magnitudes. With this approach, Figure 2b,c represent the cumulative fuel consumption in every speed phase and the total amount for each ATS configuration in cold and warm WLTCs respectively. The fuel consumption was lower in the warm cycles but the difference between baseline ATS and pre-turbine pre-DOC configurations was similar in all cases. An increase of fuel consumption was brought by the installation of the pre-turbine pre-DOC. The cumulative fuel consumption at the end of the cycle increased in 3.22% (46.7 g) and 3.89% (53.7 g) in cold and warm WLTCs respectively. On this regard, the variation in fuel consumption brought by the pre-turbine pre-DOC configuration in every WTLC phase is detailed in Figure 2b,c. In cold conditions, the pre-turbine pre-DOC configuration improved the fuel consumption during the low-speed phase (\(-3.05\%\) (\(-6.5\) g)). However, a progressive deterioration of the fuel consumption was found from the medium speed phase on. In warm cycles, the trend was similar in these medium- to extra-high-speed phases but the low-speed phase also resulted in a fuel consumption penalty for the pre-turbine pre-DOC configuration (2.96% (5.3 g)). The fuel consumption penalty has its origin in two linked pressure drop phenomena. In this study, the addition of a new element (pre-turbine pre-DOC) necessarily involves an increase of the exhaust line pressure drop, so that some fuel consumption damage was expected. Figure 3 shows the pressure drop of the ATS elements in baseline and pre-turbine pre-DOC configurations for each WLTC. The pre-turbine location contributes to decrease the pressure drop of a given element because of the higher gas density provided that the pressure at the turbine inlet is high enough to offset the higher temperature with respect to post-turbine location [26]. This condition is only fulfilled from a certain level of boost pressure. However, the pre-DOC shows high pressure drop in comparison to the DOC+SCRF during all WLTC phases. The pre-DOC pressure drop ranged 25-30% of the DOC-SCRF one in pre-turbine pre-DOC configuration. It is interesting to note that the ATS pressure drop, and in particular the pre-DOC one, was higher in the low-speed phase of the warm WTLC than in the cold one. This result contributes to explain the higher fuel penalty damage for the former during such WLTC phase. This was due to the lower gas temperature and SCRF soot loading in the cold WLTC (cold WLTC was run from clean wall-flow filter while warm WLTC did it from the soot loading corresponding to cold WLTC). The magnitude of the pre-DOC pressure drop was caused by the reduced effective \begin{table}
\begin{tabular}{l c c} \hline \hline  & **DOC** & **Pre-DOC** \\ \hline Substrate & Cordierite & Metallic \\ Channel cross-section & Square & Triangular \\ Diameter [mm] & 125 & 30 \\ Length [mm] & 70 & 85 \\ Volume [cm\({}^{3}\)] & 860 & 60 \\ Cell density [cpsi] & 400 & 300 \\ Cell size [mm] & 1.16 & 2.1 \\ Wall thickness [mm] & 0.11 & 0.08 \\ Catalytic area [m\({}^{2}\)] & 2.22 & 0.175 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Geometrical parameters of the oxidation catalysts. cross-section of the monolith. Although it had the same diameter than the turbine inlet, the open frontal area (OFA) distorted the flow path due to the decrease of the effective section by 18% (OFA = 0.82). The addition of this pressure drop to the exhaust path penalizes the engine backpressure by itself, but also induces a negative effect on the boost control, as described next. On the one hand, the pre-turbine location directly affects the amplitude of the instantaneous pressure pulses at the turbine inlet.