## 4 Results and Discussion
### Assessment of the POCS Pressure Drop
#### 4.2.2 Exhaust Line Equipped with EHC-POCS Assessment  
The results related to the application of the EHC-POCS as a pre-catalyst are reported. In particular, the obtained data of two different scenarios (with and without the designed structure) are analyzed in order to evaluate the application of the EHC-POCS and the resulting beneficial effects in terms of ATS performances. The EHC operating conditions are selected to exploit the electrical heating sensitivity analysis: 38.0 V for a total of six seconds. At first, the heat transfer phenomena occurring in the first portion of a single exhaust manifolds are investigated  
Figure 12: Electrical heating sensitivity analysis: struts’ domain average temperature profiles. Figure 13: Electrical heating sensitivity analysis: struts domain maximum temperature profiles. in case the EHC-POCS is equipped in the exhaust line. To carry out a consistent comparison, the thermal response of the same first portion of the exhaust manifold is simulated excluding the presence of the designed structure. The analysis of the obtained temperature profile at the outlet of the considered geometry provides a clear understanding of the effects related to the electrical heating application and to the fluid-POCS heat transfer phenomena. In particular, the outlet temperature profiles computed through the two different simulations, superimposed over the inlet temperature trend, are shown in Figure 14.  
The heating strategy is effective in increasing the temperature of the fluid flow. In particular, the achieved temperatures are such that the catalytic reactions are active in the first seconds of the cold start, which are commonly referred to as the most critical phases and are responsible for most of the pollutants emissions. As soon as the electrical heating is deactivated, the thermal inertia of the EHC-POCS is such that part of the fluid enthalpy is employed to heat up the designed structure. Two seconds after the deactivation, the EHC-POCS structure is responsible for lower outlet temperatures than what can be observed for the case without POCS. To account for the effectiveness of the obtained pre-catalyst behavior, the pollutants' percentage abatements are computed and their profiles all over the simulated time-range are presented in Figure 15. Considerable pollutant abatement is achieved three seconds after the engine cold start, which is approximately 20% for all the considered pollutants. Figure 14: EHC–POCS influence on the fluid temperature profile. Figure 15: Pollutant abatement with the activation of the EHC–POCS structure. After the initial activation of the catalytic reactions, the pollutant abatement increase is slowed down around the time instant corresponding to 5 s: the maximum exhaust gas mass flow is being discharged while the gas temperatures are still below the characteristic reactions' light-off values. As a consequence, even though the electrical power is continuously being supplied, the local maximum temperatures are slightly reduced. As time advances and the inlet fluid temperatures increase, the pre-catalyst is more and more effective. The final CO, NO and HC percentage abatements are approximately 45, 40, and 32%. The analyzed data prove the effectiveness of the pre-catalyst, resulting in higher fluid temperatures during the initial phases of the cold start and a considerable reduction in the pollutant emissions prior to the standard ATS devices. A visualization of the HC pollutants concentration and fluid temperature distributions for different selected time instants is presented in Figure 16. A minimum temperature threshold equal to 500 K is employed in order to identify the domain portions where the catalytic activity is expected. From a qualitative point of view, it is possible to appreciate how the electrical power supply is effective in increasing the fluid temperature which grows as the radial distance from the POCS decreases (Figure 16a,b). Once the heating strategy is over, the fluid temperature distribution is ruled by the imposed inlet profile (Figure 16c,d).