Open-Loop Study (No PID Controllers)

The open-loop study was performed for investigating the hardware capabilities without any effects from the tuning of the PID controllers. Figure 25 reveals the importance of the initial level of power, as well as the average power provided to the compressor. Cases with the maximum amount of power provided during the first section benefit from the fastest response and highest BMEP levels. On the other hand, Figure 25b shows that the power distribution is equally important as the average power provided to the compressor for a fast transient response time.

**Figure 25.** Open-loop load tip-in results at 1600 rpm engine speed: (**a**) BMEP vs. time; (**b**) average power vs. time to torque; colour and symbol categorization indicates the amount of power provided during the first section.

### 4.2.2. Fixed Gear Vehicle Speed Transient

The results in Figure 26 illustrate the required time for increasing the vehicle's speed from 1100 to 3000 rpm. As is expected, an aggressive tip-in leads to a fast vehicle speed transient. The pre-turbine pressure has almost a negligible effect on the required time. The comparison between the e-turbo and the baseline engine for the 2–16 BMEP shows the improvement in transient response for the electrically-assisted model. On the other hand, the comparison for the 2–4 BMEP tip-in shows no difference at all due to operating at the non-boosted area of the engine. Figure 26b demonstrates the amount of energy provided or harvested by the motor during the transient period of interest. It is clear that during the first phase of the tip-in, the motor provides a high amount of power (limited to 5 kW) to the compressor for meeting the BMEP demands. Once the targeted boost pressure is achieved, the e-turbo starts harvesting energy for most of the cases. The overall average energy demand is negative (energy generation) for most of the cases, except the most aggressive one, as shown in Figure 26b, where the BMEP is increasing for the whole duration of the transient as presented in Figure 26c. The Brake-Specific Fuel Consumption (BSFC) of the engine is slightly deteriorated when higher pre-turbine pressures than the baseline model are applied, as shown in Figure 26d.

**Figure 26.** *Cont.*

**Figure 26.** Fixed gear vehicle speed transient results; % values represent pre-turbine pressure increase compared to the baseline engine: (**a**) engine speed vs. time; (**b**) motor-generator power vs. engine speed; (**c**) BMEP vs. time; (**d**) Brake-Specific Fuel Consumption (BSFC) vs. engine speed.
