## 3 Results and Discussion
### Emission Performance
This is consistent with experimental results  
Figure 14: The change in gas temperature in the active cylinder with respect to crank angle for the normal operation and two CDA modes at an engine speed of 450 rpm and an engine load of 1000 N\(\cdot\)m (the calculated results were obtained from 3D simulation of ESE DIESEL). of the relationship between the EGR rate and BSNOx in [64] and results of NOx formation suppression by high excess air ratio in [65]. Figure 16 shows the effect of the different EGR rates on CO and Soot emissions under the CDAc + EGR mode at a speed of 450 rpm and a load of 1000 N-m. Increasing the EGR rate from 0% to 50%, the BSCO emission is increased by 8 g/(kW-h), which is close to double the CO emission level at the 0% EGR rate. This is because EGR effectively suppresses the reaction rate of CO oxidation in combustion and reduces the combustion temperature, retarding the evaporation of liquid fuel drops on the surface of the cylinder wall. With the different EGR rates, the BSSoot emission is relatively stable and remains at the level of 0.0025 g/(kW-h), which is close to being negligible. Although the raised EGR rate leads to a longer combustion delay period (see Figure 17) and decreases the generation rate and oxidation rate of soot, however, the soot oxidation process occurs more completely due to sufficient combustion time. The results are consistent with the conclusions reported in [63; 64; 66]. Although the increased EGR rate decreases BSNOx emissions effectively, the BSFC and the BSCO emissions are increased. Figure 16: BSCO–BSNOx trend and BSsoot–BSNOx trend for the CDAc + EGR mode with the EGR rate from 0% to 50% at an engine speed of 450 rpm and an engine load of 1000 N-m (the emission results were transformed from 3D simulation of ESE DIESEL). Figure 15: BSFC–BSNOx trade-off for the CDAc + EGR mode with the EGR rate from 0 to 50% at an engine speed of 450 rpm and an engine load of 1000 N-m (the emission results were transformed from 3D simulation of ESE DIESEL). According to the comparison above, the optimal option is that the EGR rate is 30%, in which the BSNOx emission is effectively reduced to 4.2 g/(kW\(\cdot\)h) at the cost of a 0.8% increase in the BSFC and without the increase in the BSCO emission. Although EGR causes a slight BSFC increase, it is far less than the BSFC reduction brought by CDA. The post-turbine exhaust gas temperatures are illustrated in Figure 18 for the load of 1000 N\(\cdot\)m. At the CDAo mode, the exhaust gas temperature marginally declines since air with a lower temperature in deactivated cylinders flows into the exhaust pipe, which has a cooling effect on the exhaust gases from the active cylinder. Compared with the normal mode, the exhaust gas temperature is increased by 50 K at the CDAc mode and by 70 K at the CDAc + EGR mode. This can be explained that the deactivated cylinder is isolated from the exhaust pipe, so the charge in the cylinder does not enter the exhaust pipe, which leads to due to nearly twice more heat release from fuel combustion, which exceeds the stable working temperature for diesel engine aftertreatment, ensuring high catalytic efficiency to improve emissions. Higher exhaust gas temperatures are reached that reflect the reduced gas-side heat transfer (Figure 9), which is attributed to the fact that the increased heat transfer losses in the firing cylinders are more than offset by the lower heat transfer losses in the disabled cylinders, and the recovery of exhaust gas thermal energy heating the intake air. Figure 17: Soot formation in the active cylinder under the CDAc + EGR mode with the EGR rate from 0% to 50% at an engine speed of 450 rpm and an engine load of 1000 N\(\cdot\)m (the calculated results were obtained from 3D simulation of ESE DIESEL). Figure 18: The exhaust gas temperature for the normal operation and CDA modes at an engine speed of 450 rpm and engine loads of 1000 N\(\cdot\)m and 4000 N\(\cdot\)m (the calculated results were obtained from 1D simulation of GT-SUITE).