## 4 Results
### Test Results Versus Map Results  
Additionally, an engine mapping study under steady-state conditions was performed to analyze the engine behavior in all possible operating situations. In order to achieve that, the mapping ranged from 1000 rpm to 3500 rpm every 100 rpm, combined with 10% of throttle increments. The CO2 and NOx emissions are represented in Figure 10. The operating area of RDE 1 is also represented by dots on the contour plots, which are devoted to CO2 and NOx emissions. As observed in Figure 10a, the maximum CO2 emission was located in the top right corner, whilst the minimum was at the bottom left one. However, Figure 10b shows how NOx emissions were mainly influenced by the EGR rate, which is different depending on the operative engine conditions although lower as the load and speed increased. A comparative study of CO2 and NOx emissions obtained from the RDE tests and the steady-state results from the engine map was performed considering the engine speed and throttle during the cycles. Figures 11 and 12 show the instantaneous CO2 and NOx emissions of RDE 1 versus the emissions obtained by interpolation in the engine maps. Figure 9: Comparison of Urban (**a**), Rural (**c**) and Motorway (**e**) CO2 emissions and Urban (**b**) Rural (**d**), and Motorway (**f**) NOx emissions, and engine speed between RDEs 5 and 6. As observed in Figure 12, a very good correlation exists between the instantaneous measured values during the tests and the emissions extracted from the maps. The divergencies produced are due to interpolations errors, especially in the case of NOX, since these do not have a total linear behavior. Making a deeper analysis, Figures 13a-c and 14a-c show three fractions of 150 s of CO2 and NOX emissions in RDE 1 corresponding to urban, rural, and motorway driving phases, respectively. Absolutes differences between emission concentrations in dynamic and steady operation are presented in Figures 13d-f and 14d-f. Finally, Figures 13g-i and 14g-i represent the distribution of the emissions absolute error for these species. As can be observed, urban zones show the worst correlation due to their more dynamic feature. However, rural and motorway zones were characterized by quasi-steady operation, where the vehicle speed was almost constant, so that the engine solicitations did not change significantly. In any case, a good correspondence was obtained between RDE and steady-state maps, especially for fuel consumption. Figure 11: RDE 1 CO2 [g/s] emissions test versus engine map. Figure 10: CO2 [g/s] (**a**) and NOX [g/s] (**b**) emission from engine maps (color scale) and those obtained from the tested cycle (dots). Figure 12: RDE 1 NO\({}_{\rm X}\) [g/s] emissions test versus engine map. Figure 13: CO\({}_{2}\) emissions comparison between RDE 1 and engine map in urban (**a**,**d**,**g**), rural (**b**,**e**,**h**), and motorway (**c**,**f**,**i**) driving phases. Table 7 shows the comparison of the CO\({}_{2}\) and NO\({}_{\rm X}\) emissions data for all tested RDEs. The corresponding errors are also presented. This summary of the results points out very small differences between pollutants measured during the tests and pollutants extracted from a steady-state engine map. In the case of CO\({}_{2}\) emissions, the correlation is better, having errors around 1%, which fell into the measurement error margin of the measuring device. In the case of NO\({}_{\rm X}\) emissions, the deviation from the engine map estimate increased, but it was still low enough to provide understanding about the driving cycles effects as a function of their definition, especially keeping in mind the use of state-of-the-art NO\({}_{\rm X}\) aftertreatment systems of high conversion efficiency. Looking at CO\({}_{2}\) errors in Table 7, the largest errors were found in the RDEs 1, 2, 3, and 4 cycles, i.e., the specific emissions were also maximum. On the contrary, RDEs 5 and 6 presented the lowest errors.