## 3 Results and Discussion
### Energy Analysis for the Engine  
The effect trends of CDA on the BSFC at engine speeds of 450 rpm and 556 rpm are similar (Figure 7), so energy analysis is performed at 450 rpm and 1000 N-m. The change in the engine indicated efficiency \(\eta_{i}\) depends on the indicated efficiency \(\eta_{i,act}\) in the active cylinder and the motoring losses in the deactivated cylinder. Figure 8 shows the indicated efficiency of the engine and the active cylinder at an engine load of 1000 N-m and an engine speed of 450 rpm. The indicated efficiency \(\eta_{i,act}\) of the active cylinder is increased by 3.28% for the CDAo mode and by 4% for the CDAc mode. This can be explained by the fact that, when half of the cylinders are deactivated, more fuel mass is injected into the active cylinder with higher injection pressure. As shown in Figure 6, the maximum injection pressure increases from 198.7 bar at the normal mode to 373.1 bar at the CDAc mode and to 376.1 bar at the CDAo mode. The increased injection pressure accelerates fuel atomization and evaporation and promotes the mixture formation process [60]. More mixture is formed during the ignition delay period, which leads to an increase in combustion heat release rate at the rapid combustion period (Figure 9). The proportion of tail combustion heat release in the whole combustion decreases, thus improving the effective efficiency of the active cylinder. However, this benefit for the BSFC reduction in the active cylinder is offset by the motoring losses in the deactivated cylinder, which is expressed as a closed curve area in Figure 10 (V/V\({}_{a}\)--the ratio of the above piston space to the total work volume). For the CDAo mode,  
Figure 8: Comparison of the indicated efficiency for the engine and the active cylinder at an engine speed of 450 rpm and an engine load of 1000 N-m (the calculated results were obtained from 1D simulation of GT-SUITE). trapped air in the deactivated cylinder is compressed to a higher pressure and temperature in the compression stroke, p\({}_{i}\) (the average indicated pressure--reflect the motoring losses) in the deactivated cylinder \(-\)0.3 bar, but for the CDAc mode, this value is decreased to \(-\)0.04 bar due to less mass compressed in the deactivated cylinder. Combining the changes in the motoring losses and the cylinder-indicated efficiency, the engine-indicated efficiency for the CDAo mode is reduced by 0.7% and is increased by 2.8% for the CDAc mode. The obtained calculation results prove the possibility of fuel consumption improvement using CDA by transforming cylinder work operations from low efficiency to high efficiency. Closing all valves in the deactivated cylinder reduces the motoring losses to reduce fuel consumption. Figure 11 shows the comparison of the energy distribution diagram at the normal mode (N) and two CDA modes at an engine speed of 450 rpm and a load of 1000 N-m. Ensuring the same brake engine power N\({}_{e}\), the friction losses N\({}_{t}\), pumping losses N\({}_{p}\)  
Figure 10: The normalized P-V diagram in the deactivated cylinder under the CDAo mode and CDAc mode (the calculated results were obtained from 1D simulation of GT-SUITE). Figure 9: The normalized P-V diagram and combustion heat release at different modes (the calculated results were obtained from 1D simulation of GT-SUITE). heat transfer losses \(\rm N_{h}\), and exhaust energy \(\rm N_{ex}\) are analyzed and compared. The heat transfer loss is increased at the CDAo mode due to the higher combustion temperature in the active cylinder. At the CDAc mode, disabling all valves in the deactivated cylinders, the heat transfer losses to cylinder walls are decreased. This can be explained that the exhaust-intake strokes are replaced by the expansion-compression strokes, during which the irreversible pressure change produces the motoring losses, which are slight compared with the brake engine power. The average pressure of the motoring losses is \(-0.04\) bar, equivalent to half the pumping losses of a normally worked cylinder at the same engine load.