## 3 Results and Discussion
### Emission Performance  
The calculated results on the brake-specific pollutant emissions of the investigated engine under the normal mode and CDA modes at an engine speed of 450 rpm were given in Figures 12 and 13. According to the result in Figure 12, in comparison with the normal engine operation, all CDA modes lead to a decrease in CO emission. At the engine load of 1000 N\(\cdot\)m, the CDAo mode results in a reduction in CO emission from 42.98 to 10.63 g/(kW\(\cdot\)h) (by 75.26%). This reduction is mainly attributed to the higher injection pressure (see Figure 6) in the active cylinder, promoting the quality of fuel-air mixing, and the increased  
Figure 12: The brake-specific carbon monoxide (BSCO) (**a**), the brake-specific nitrogen oxides (BSNO) (**b**), and the brake-specific soot emission (BSsoot) (**c**) 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 emission results were transformed from 3D simulation of ESE DIESEL). Figure 13: Comparison of soot formation in the active cylinder between 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). combustion temperature (see Figure 14), which improved the evaporation of fuel on wetted in-cylinder surfaces. Enhanced fuel-air mixing and heat release due to higher injection pressure have also been reported in [61]. The relationship of CO emission with the fuel injection and temperature in the cylinder is in accordance with the results in [62]. As can be seen from Figure 12, the soot emission can almost be neglected at the load of 1000 N\(\cdot\)m and 450 rpm. Both CDA modes reduce soot emission from 0.0070 g/(kW\(\cdot\)h) to 0.0026 g/(kW\(\cdot\)h) (by 62.9%). By tracking the change in the soot emission with the crankshaft angle (Figure 13), it can be found that in comparison with the normal operation, the increased fuel injection mass in the active cylinder at both CDA modes leads to a richer mixture (under the premise of the same intake air mass), and more intensive formation of soot happens near the TDC. However, the formed soot is mainly oxidized on the expansion cycle. At two CDA modes, soot oxidation is promoted attributed to the increased temperature on the expansion cycle (Figure 14). A weak influence of the valve closure on soot emissions is observed. The NOx emission is obviously higher under CDA modes compared with normal operation due to a higher combustion temperature. In comparison with the CDAc model, the BSNOx emission for the CDAo model increases by 7.1 g/(kW\(\cdot\)h) due to a higher combustion temperature. This can be explained that the pumping losses and mechanical losses for the CDAo mode are higher due to the normal valve motions; in order to maintain engine output power, the cycle amount of fuel injected into the active cylinder is increased by 31 mg/cycle, which leads to a higher heat release rate and combustion temperature (see Figure 14). The reduction in NOx emissions was achieved by changing the EGR rate (adjusting the EGR valve opening angle). Figure 15 shows the effect of the change in the EGR rate (from 0 to 50%) at the CDAc + EGR mode at a speed of 450 rpm and a load of 1000 N\(\cdot\)m on the BSFC and NOx emissions. When the EGR rate is gradually increased from 0 to 50%, BSNOx emission is reduced by 18 g/(kW\(\cdot\)h), and the BSFC is increased by 12 g/(kW\(\cdot\)h). This can be explained by the fact that the higher mass fraction of exhaust gas in the intake charge leads to a lower excess air coefficient in the active cylinder, which leads to a decline in combustion efficiency [60; 63]. The effect of EGR in suppressing BSNOx emissions becomes less obvious as the EGR rate increases.