## 3 Results
### Pollution Centered Scenario  
One can see the performance of the pollution centered scenario in Figure 21 (in this case, the weighting parameter, \(\alpha\), is equal to \(5\)) compared to the reference strategy. Fuel consumption increases by \(15\%\), but we observe a great reduction in pollutant emissions: \(73\%\) for CO, \(57\%\) for HC and \(84\%\) for NO. Numerical results are presented in Table 4.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Ref. Strategy** & \(\alpha=5\) & **Relative** \\  & \(SA_{opti}\) & \(SA\ var\) & **Variation** \\  & \(\mathbf{\phi=1.0}\) & \(\mathbf{\phi\ var}\) & \\ \hline
**Consumption** & \(6.57\) & \(7.59\) & \(+15\%\) \\
**(L/100 km)** & \(0.53\) & \(0.144\) & \(-73\%\) \\ \hline HC (g/km) & \(0.056\) & \(0.024\) & \(-57\%\) \\ \hline NO (g/km) & \(0.212\) & \(0.035\) & \(-84\%\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Performance of the pollution centered scenarios compared to the reference strategy (NEDC).  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Component** & **Size** & **Type of Model** \\ \hline Internal combustion engine & \(1.8\) L & Mean Value Engine Model \\ \hline Three way catalytic converter & EURO 6 compliant & \(0\)D model \\ \hline Chassis (Peugeot 308 SW-2009) & \(1470\) kg & longitudinal forces \\ \hline \hline \end{tabular}
\end{table}
Table 3: Main vehicle characteristics and types of model used in this study.  
Figure 20: NEDC driving cycle speed and gearbox ratio.  
As it can be seen in Figures 22 and 23, the catalyst light-off (instant where catalyst efficiency reaches 50% which corresponds to a temperature of 280 \({}^{\circ}\)C) is reached at 140 s. At this time, more than 80% of total CO have already been emitted, while almost 70% of total HC are produced. 50% of total tailpipe NO have already been dispersed in the environment.  
Figure 21: Optimal results over NEDC cycle.  
Figure 23: Cumulated emissions (reference strategy); red star: TWC light-off.  
Figure 22: Thermal behavior of the catalyst (reference strategy); red star: TWC light-off.  
The behavior of the engine is far different with the pollution centered scenario (see Figure 24): the light-off of the catalyst is quicker, as it happens after only 60 s. Furthermore, a very small amount of pollutant is emitted during this period as illustrated in Figure 25: CO are reduced by a factor of 15, HC by 4, and NOx emissions before light-off are 11 times lower than in the nominal configuration.  
Figure 26 shows the positions of the actuators during the pollution centered scenario: We can distinguish between two different behaviors:  
* Catalyst light-off: during this period, we observe a late spark advance (10 to 15\({}^{\circ}\) compared to optimal ignition). This is combined with a lean mixture, \(\Phi=0.9\). These two parameters increase the exhaust gas temperature. For constant engine torque, the reduced fuel conversion efficiency associated with late combustion requires greater fuel and air flow rate (see intake pressure in Figure 26). As a consequence, exhaust enthalpy and convective effects are high. This shortens the period where catalyst efficiency is low.
* warm catalyst period: the strategy adopts a stoichiometric combustion which represents a good compromise to oxidize CO and HC while reducing NOx. In the same time, we observe a relative delay in spark advance to lower exhaust gas temperature and reduce NO (and HC to a lesser extent) formation. The emission of CO depends only on the fuel/air ratio (see Equation (1)) of the mixture, and stoechiometry is a  
Figure 24: Thermal behavior of the catalyst (pollution centered scenario); red star: TWC light-off.  
Figure 25: Cumulated emissions (pollution centered scenario); red star: TWC light-off.  
good compromise for this pollutant. This delay increases with the brake power as it can be seen in the extra urban part of the NEDC cycle, again to lower NO emissions.