## 4 Results and Discussion
### Assessment of the POCS Pressure Drop
#### 4.1.2 One-Dimensional Performance Simulation  
The full-load behavior of a single bank of a V12 reference engine was investigated. In particular, a dedicated approach needs to be formulated to couple the 1D description of the friction effects and the obtained pressure differences across the POCS by means of the 3D simulations. The value of the friction coefficient \(f_{w}\) was determined by means of the upscaling of the pressure drop results obtained from the detailed CFD simulation of the POCS. The achieved friction factor results in 0.61. The obtained results are reported in Figure 10, analyzing the impact of the POCS presence on the engine behavior in terms of brake power and brake specific fuel consumption.  
Figure 10: Assessment of the POCS pressure drop: 1D performance simulation—brake power and brake specific fuel consumption: reference vs. POCS.  
Figure 9: Assessment of the POCS pressure drop: qualitative estimation of the computational grid effects. Fluid pressure field visualization. (**a**) mesh A-Straight; and (**b**) mesh C-Straight.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Velocity** & 0.5 & 1.0 & 5.0 & 10.0 & 25.0 & 50.0 \\
**(m/s)** & & & & & & \\ \hline
**Reynolds** & & & & & & \\
**number (-)** & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 5: Assessment of the POCS pressure drop: fluid flow Reynolds numbers.  
As expected, the influence of the POCS structure is negligible for low rotational speeds, the flow velocities in the exhaust manifolds being relatively small. If higher rotational speeds are considered, the flow velocity is such that the flow resistance is significant, inducing a relevant engine backpressure that influences the performances of the power unit. In particular, Table 6 reports the maximum percentage reduction, in terms of brake power and total efficiency, and the brake specific fuel consumption (BSFC) percentage increase obtained by comparing the reference and the POCS equipped cases. All the maximum values are obtained for the 9000 rpm regime.  
Given the expected interaction in the first phases of a cold start between the exhaust gases and the POCS, a potential difference higher than 20.0 V is required: the identified maximum average temperature is slightly higher than 500 K and no beneficial effects in the cold start abatement efficiencies are expected below the highlighted temperature. However, the associated supplied electrical power would exceed 500 W for a single duct; the application of such a structure in all the exhaust manifolds could significantly affect the vehicle battery's operational life. In addition, the maximum temperature that characterizes the POCS struts after the simulated five seconds could exceed the material limit temperature. The maximum values for each investigated condition are reported in Figure 13. Nonetheless, the interaction between the cold exhaust gases and the struts could limit the achieved maximum temperatures, ensuring that the material limits are respected. For this reason, the formulated heating strategy is modified and a total of six seconds of electrical heating are applied for the cold start assessment simulations. Even though the overall supplied electrical power could be critical for a real exhaust line application, the 38.0 V operating condition was selected for the cold start assessment. As such, the maximum capability of the EHC-POCS could be investigated.