## 4 Results and Discussion
### Assessment of the POCS Pressure Drop
#### 4.2.2 Exhaust Line Equipped with EHC-POCS Assessment
In addition, the pollutant abatement due to the washcoat-induced catalytic activity corresponding to the struts walls can be appreciated. The proposed results are employed as boundary conditions for the exhaust line simulations. As such, the beneficial effects of the EHC-POCS equipment can be investigated, both in terms of the increase in the catalysts' temperature and the pollutant abatement prior the ATS devices. An evaluation of the thermal transient of the first catalyst is presented in Figure 17. In particular, the surface average temperature of four different sections are analyzed over the simulated time-range. The selected axial coordinates for which such an evaluation is carried out corresponds to the inlet, 25 mm after the inlet, mid, and outlet coordinates. Figure 16: Cold start assessment: EHC–POCS single manifold—HC concentration and temperature distributions. (**a**) time = 2.5 s; (**b**) time = 5.0 s; (**c**) Time = 7.5 s; (**d**) time = 10.0 s.  
The electrical heating phase results in a significant spur of the heating of the first portion of the CAT1. After five seconds, the temperature of the inlet section for the ATS configuration equipped with the EHC-POCS is 100 K higher than what can be observed for the reference case. However, once the electrical heating strategy is over, the presence of the EHC-POCS induces a heat loss that becomes significant as the exhaust gas temperatures increase: the initial spur is gradually recovered until the heat transfer between the exhaust gases and the designed POCS results in an overall cooling of the fluid flow. In particular, the inlet section temperature profile of the reference case overcomes the profile of the ATS equipped with the EHC-POCS after eight seconds, while the 25 mm and mid-sections after eleven and sixteen seconds, respectively. The improved heating of the first portion of the CAT1 catalyst can be additionally analyzed by evaluating the temperature fields of the device for the two different configurations. In particular, the distribution of a slice of the temperature fields for two selected time intervals is presented in Figure 18, referring to half and to the end of the applied electrical heating strategy. Figure 17: Cold start assessment: CAT1 thermal transient evaluation. Figure 13:0 Cold start assessment: CAT1 temperature fields comparison—POCS vs. reference ATS: (**a**) time instant 3 s: half of the heating strategy; and (**b**) time instant 6 s: end of the heating strategy. However, the exhaust gas mass flow rates and the pre-defined voltage boundary conditions are such that the overall energy contribution that is provided to the catalytic substrate is limited. In addition, the EHC-POCS structures are located in the initial portion of the exhaust manifolds: before reaching the standard catalyst, the heated fluid flow exchanges a significant amount of wall heat power with the exhaust manifolds. As a consequence, at the end of the heating strategy, only a small portion of the ATS device was significantly heated up. As the exhaust gas flow rates and temperatures increase, the induced heat transfer between the hot gases and the designed POCS are responsible for a significant reduction in the first catalyst temperature with respect to the reference case. The temperature field distributions of the first catalyst at the simulation end-time is reported in Figure 19 for both of the ATS configurations analyzed. In particular, different regions featured by a temperature difference of 100 K have been highlighted through the identification of temperature iso-lines. Only the thermal transient of the first catalyst was investigated, while the second substrate was not considered. The simulated operating conditions are such that no relevant effects affect the thermal response of the second catalyst. Indeed, at the simulation end-time, the outlet temperature of the CAT1 increased by approximately 50 K only under the assigned initial conditions. The thermally related effects discussed herein are strongly coupled to the obtained pollutants' conversions.