## 5 EGH Optimization
In this figure, it can be observed that the time a long-haul HDV spends at 1000 rpm (50 km/h) is about 12 min (suburban conditions). Figure 9: Theoretical and experimental SCR conversion efficiency as a function of catalyst temperature. Figure 11: Speed profile of a long-haul heavy-duty vehicle [28]. Table 3 summarizes the power requirements of the EGH to achieve 95% of conversion efficiency. \begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Test**} & \multicolumn{2}{c}{**Engine**} & \multirow{2}{*}{
\begin{tabular}{c} **Speed** \\ **(km/h)** \\ \end{tabular} } & \multirow{2}{*}{**Road**} & \multicolumn{2}{c}{**EGH Peak**} & \multicolumn{2}{c}{**Average**} & \multicolumn{2}{c}{**Time *} \\  & **(rpm)** & & & & & **(kWh)** \\ \hline
1 & 1000 & 55 & Suburban & 5.02 & 2.18 & 12 min & 0.436 kWh \\ \hline
2 & 1250 & 68 & Interurban & 2.17 & 0.28 & 61 min & 0.285 kWh \\ \hline
3 & 1500 & 82 & Highway & 0.36 & 0.05 & 115 min & 0.095 kWh \\ \hline \hline \end{tabular}   
* Taken from the real speed profile of a long-haul HDV presented in Figure 11.  
As seen in the Table 3, optimum consumption values are within a realistic range of an on-board generator, between 5.02 kW and 0.36 kW. These values have been extracted from maximum points achieved in Figure 10 for each regime. Then, the average power and energy has been calculated considering the real mission profile presented in Figure 11. Note that the most demanding regime is the suburban driving, which contrasts with the fact that it is the shortest of the three. The total energy required by the EGH during the Figure 11 mission profile will be 0.816 kWh. Figure 10: Theoretical power consumption of the EGH to achieve the SCR light-off temperature of 220 \({}^{\circ}\)C at 1000 rpm, 1250 rpm and 1500 rpm. \begin{table} \end{table} 
Table 3: EGH power requirements to achieve 95% of SCR efficiency. The easiest solution to provide this additional energy would be the use of a supplementary alternator. Most factory alternators for HDVs are available with outputs ranging from 160 up to 320 amps (3.84 kW to 7.68 kW) and can handle the vehicle's basic necessities, such as headlights, gauges, fuel pumps, A/C, etc. Considering this power production range, the inclusion of a 5.02 kW EGH (i.e., to fulfil EURO VI) into the electrical system would require incorporating an exclusive alternator for the EGH, causing a significant increase in fuel consumption. A 200 A alternator can produce the amount of power required by a 5 kW EGH. However, its use will cause an increase on the vehicle's fuel consumption because when the alternator works under load conditions, it exerts an additional force on the engine shaft [11]. Under the worst conditions of Table 3, the fuel consumption would increase by 1.43%. A hot air flow bench was used to analyze the backpressure caused by the EGH in the exhaust pipe. The maximum backpressure was 1.8 mbar at 204 g/s. From this data, the hydraulic power, \(P_{H_{EGH}}=Q_{EGH}\cdot\Delta p_{EGH}\), that the motor must exert to overcome the EGH additional back pressure is calculated. The greatest impact occurs during highway conditions (1500 rpm and 90%FTPP) with \(P_{H_{EGH}}=\frac{0.204\frac{\text{kg}}{\text{kg}}\cdot 180\text{ Pa}}{0.745\text{ kg/m}^{2}}=49.3\text{ W}\). This means that the required engine power increase in 49.3 W. Taking the power developed by the vehicle at that regime and the \(P_{H_{TATH}}\), this would suppose a fuel consumption increase of 0.015%. On the other hand, the additional weight that the EGH adds to the vehicle must also be considered. A heavier truck produces more rolling resistance than a lighter one, thereby increasing the power needed to move the vehicle. A 200 kg cut in vehicle weight can reduce fuel consumption by 0.5% on a regional delivery truck and 0.3% on a long haul truck [29]. Considering a EGH weight of 10 kg, this would suppose a fuel consumption increase of 0.025%. Other study [30] established that the average impact on mpg per ton of increased payload of a HDV with a fuel consumption of 8.15 mpg is 0.112 mpg.