shows the GT-Power simulation model of the test engine mentioned in the previous section. The parameters in this simulation model corresponded to the original 4RB2 engine as shown in Table 1. cylinder #1 and #4 were the combustion cylinder, and cylinder #2 and #3 were the expansion cylinder. The exhaust valve of combustion cylinders and intake valve of expansion cylinders were connected by a connecting chamber. The valve timing is shown in Fig. 4(b), and the valve timing parameters are shown in Table 2. If the expansion cylinders change their operation to the 2-stroke working mode. The valve timing of 2-stroke working mode shown in Fig. 4(a). The valve timing parameters of the 2-stroke working mode, such as intake advance angle, intake duration, exhaust advance angle, exhaust duration, and overlap duration, remained the same with the 4-stroke working mode.