## 3 Results and Discussion
### Basic Parameters for the RCCI-SHV Operation
#### 3.1.2 ICE Operating Conditions Selection  
The rule-based control (RBC) charging concept relies on defining pre-established operating conditions to charge the battery whenever it is required [46]. However, the same power can be delivered by changing the total time that the engine is operating and the operating condition of the engine. As a result, the same fuel consumption will not be achieved. In addition, the battery charging can be done using a different number of operating conditions, for example, one condition of average power or two different conditions, one with lower power and the other with a higher power value. For this reason, a parametric study aiming to understand the effect of using one, two, or three operating conditions to charge the batteries was performed, which will serve to define the best strategy for the hybrid concept. All the conditions selected are inside the RCCI zone to take advantage of the benefits  
Figure 8: Instantaneous state of charge (SOC) (**a**) and final fuel consumption (**b**) for different initial SOC at the worldwide harmonized light vehicles test cycle (WLTC) driving cycle.  
Figure 9: Instantaneous SOC (**a**) and final fuel consumption (**b**) for different initial SOC at the RDE driving cycle.  
in terms of efficiency, NOx, and soot emissions. The three operating conditions selected (19, 23, and 32 kW) to perform the parametric study are marked in Figure 10.  
Figures 11 and 12 show the instantaneous SOC and fuel consumption along the WLTC and RDE cycle, respectively, for the cases of using one, two, or three ICE operating points. Figure 11 shows slight differences for the initial phases of the driving cycle. In these conditions, the battery is mainly charged by the energy recovered through regenerative braking, while the ICE is started during only a few intervals. After 1000 s of the cycle, the SOC profiles for the three strategies become distinct as a function of the higher power requirement. However, the great differences are observed in the highway phase, where the vehicle reaches speeds higher than 100 km/h. In this case, when three operating conditions are used, it takes a short time to recharge the battery. In addition, as the number of operating conditions is increased, the SOC variation lessened compared to the case with one operating condition. Finally, it is also seen that the use of low-power operating conditions as much as possible decreases the total mass fuel consumption as its value is proportional to the power.  
Figure 12 shows similar results for the RDE driving cycle, but with lower differences in general. The only condition where it is possible to realize SOC differences is in the highway phase. For this segment, it is observed that the SOC decrease is considerably reduced as the number of operating conditions of the ICE is increased. Furthermore, the fuel consumption values also decrease for the condition with three operating points, as was found with the WLTC. Therefore, the approach based on three operating conditions to charge the battery was chosen to perform a comparative study.  
Figure 11: Instantaneous SOC (**a**) and cumulative fuel consumption (**b**) for the three-charging strategy during the WLTC driving cycle.  
Figure 10: Indicated power in the RCCI portion of the map. The three selected points to perform the parametric study are marked in the map.