## 3 Results and Discussion
### HEV Simulations with GCI Engine Test Results  
#### 3.2.1 CN35 Engine with a 48 V Mild Hybrid Configuration  
The conventional 4-cylinder, 1.6 L stock CI engine (16:1 of compression ratio) in Table 2 running on CN35 was calibrated using a DoE (design of experiments) [31] test under global operating conditions prior the final calibration on a roller test cell. Based on the combustion mode from the SCE tests, the CN35 engine was calibrated with a statistical model (ICE2 software [32]) to cover the complexity levels (high number of levels, parameters). Through the calibration of the engine, a CN35 engine map could be prepared, and the generated calibration maps could be tuned during vehicle test. The engine map, representing the sweeping engine speed and load, were then performed at the vehicle test bench to validate the engine behavior and to calculate the cumulated values of the emissions. From the vehicle test, the vehicle with CN35 addressed the vehicle test tail-pipe results, concluding that running a CI engine with CN35 fuel can fulfill the Euro 6d standard, especially when it is equipped with an ATS, i.e., a diesel oxidation catalyst (DOC), an SCR catalyst, and a DPF, providing the possibility of further CO\({}_{2}\) benefits [20; 21]. As the CN35 engine is able to operate the entire engine map, HEV simulations were performed for the CN35 vehicle with the objective of reducing CO\({}_{2}\) emissions and pollutant emissions during the driving cycle (WLTC). Figure 6 shows the coverage of the engine response for each functioning point of cold WLTC after hybridization and recalibration. The electric components that were assessed were a 48 V of battery and a 25 kW electric motor on a P2 mild hybrid configuration. The hybridization and recalibration of the engine and ATS change the engine operating areas for the driving cycle. The mean engine efficiency for the driving  
Figure 5: The GCI engine map with benefit and challenge-defined zones by fuel selections: (**a**) CN15, (**b**) CN25 and (**c**) CN35. cycle can be improved in HEV simulation by shifting the operating conditions, as the area of high engine efficiency is located at higher loads. Figure 7 represents the engine-out and tailpipe emissions on cold WLTC before and after the hybridization of the CN35 vehicle. In general, HEVs allow ICEs to operate more efficiently, resulting in less pollutant emitted. The engine-out CO and HC emissions are relatively low after hybridization because the engine can be operated over less time in cold conditions, allowing for more flexible engine operation in HEV. For these reasons, the unburnt gas emissions of the CN35 vehicle with hybridization are relatively lower than the level of emissions from the conventional CN35 vehicle. A reduction in NOx emissions as well as in the trends of the emissions can be observed and are similar to those in the tailpipe. The accumulated tailpipe emissions caused by hybridization are lower than the regulations for all pollutants with significant margins. The lower tailpipe emissions are not only due to lower engine-out emissions but are also caused by the better efficiencies of ATS system on the HEV. The efficiencies of DOC and SCR were improved with better DOC lights-off and SCR urea injections by the hybridization. From these results of low pollutant emissions, it can be observed that further CO\({}_{2}\) reductions are possible. From this HEV simulation, the CN35 vehicle was able to reduce 19% of CO\({}_{2}\) emissions through hybridization, and further reductions were possible with adaptions of the ATS and ICE models of up to 5%. Total CO\({}_{2}\) savings of up to 24.1% were achieved through the HEV simulation due to optimal engine management and ATS operating within their most favorable range of efficiency. In addition, the batteries and the electric drive allow regenerative braking which helps to recoup some of the energy lost during normal operation.