## 3 Results
### Flow Temperature Distribution at the DOC Outlet  
As commented in Section 2.2.3, it is suggested that energy recovery processes should take place downstream of after-treatment devices in order not to interfere with their operation. However, they should also occur sufficiently close in order to minimize further thermal energy dissipation to the surroundings. Therefore, the analysis of the flow abandoning the DOC is essential to know the working conditions of energy-harvesting devices.  
Low uniformity in inlet flow occurring in most catalysts leads to different flow paths with different residence times. Flow inside the DOC is subject to cooling because external convection and heating because of chemical reactions in the DOC. These different paths (see Figure 11) caused by the inlet cone cause a gradient of temperature in the outlet section of the catalytic converter, as can be seen in Figure 12.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Engine Speed** & **Torque** & **Measured** & **Modelled** & **Error in** & **Experimental Modelled** & **Error in \(\dot{Q}\)** \\
**(min\({}^{-1}\))** & **(Nm)** & \(\mathbf{T_{g\_out}}\) (\({}^{\circ}\)C) & \(\mathbf{T_{g\_out}}\) (\({}^{\circ}\)C) & \(\mathbf{T_{g\_out}}\) (\%) & **(\%)** & **(\%)** & **(\%)** \\ \hline
1000 & 10 & 94 & 96 & 1.4 & 590 & 562 & \(-\)4.9 \\
1000 & 110 & 269 & 253 & 5.9 & 2587 & 2639 & 2.0 \\
2400 & 10 & 167 & 164 & 1.8 & 1287 & 1357 & 5.4 \\
2400 & 110 & 310 & 300 & 3.0 & 3286 & 3364 & 2.4 \\ \hline \hline \end{tabular}
\end{table}
Table 10: Experimental versus model thermal results out of calibration engine modes.  
Figure 11: Streamlines and inlet velocity distribution in the monolith. An example of usual bad flow uniformity caused by inlet cones in automotive catalysts can be seen.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Engine Speed** & **Torque** & **Measured** & **Modelled** & **Error in** & **Experimental Modelled** & **Error in \(\dot{Q}\)** \\
**(min\({}^{-1}\))** & **(Nm)** & \(\mathbf{T_{g\_out}}\) (\({}^{\circ}\)C) & \(\mathbf{T_{g\_out}}\) (\({}^{\circ}\)C) & \(\mathbf{T_{g\_out}}\) (\%) & **(\%)** & **(\%)** & **(\%)** \\ \hline
1000 & 60 & 176 & 169 & 4.0 & 1384 & 1407 & 1.6 \\
1700 & 10 & 125 & 123 & 1.6 & 915 & 876 & \(-\)4.3 \\
1700 & 60 & 235 & 226 & 3.7 & 2016 & 2063 & \(-\)2.3 \\
1700 & 110 & 299 & 288 & 3.7 & 2977 & 3107 & \(-\)4.4 \\
2400 & 60 & 263 & 256 & 2.7 & 2423 & 2508 & 3.5 \\ \hline \hline \end{tabular}
\end{table}
Table 9: Experimental versus model thermal results in calibration engine modes.  
Coefficient of variation (standard deviation divided by mean value) of temperature distribution across the DOC outlet area (distribution shown in Figure 12b) was calculated from results of the CFD model. This statistical coefficient accounts for the dispersion from the average temperature flow. As can be seen in Figure 13, variation in temperature is enhanced in engine conditions with low mass flows, since flow thermal inertia is also lower. Engine modes in which catalytic reactions are active (see black dots in Figure 13) present more uneven distribution than those in which they are inactive (see white dots in Figure 13).