## 3 Results and Discussions
### Influence of Ventilation Temperature and Ventilation Volume  
Usually, increasing ventilation volume and decreasing ventilation temperature can improve the ventilation efficiency [20]. However, improperly increasing the air volume or reducing the inlet temperature may increase economic cost and discomfort. Therefore, how to choose the optimal combination of ventilation rate and temperature is a worthy research pursuit [21]. A set of comparative simulations was carried out to investigate the effects of the ventilation temperature and ventilation volume on the ventilation performance. According to the operating conditions of the equipment and ventilation specifications, the maximum temperature of the engine room should not exceed 55 \({}^{\circ}\)C. As a result, we investigated three different ventilation temperatures and three different ventilation volumes in the simulation analyses. The parameter settings were (1) ventilation temperature 45 \({}^{\circ}\)C with three different volumes; (2) ventilation temperature 40 \({}^{\circ}\)C with three different volumes; and (3) ventilation temperature 35 \({}^{\circ}\)C with three different volumes. Figures 7-9 depict the cloud map of high-temperature volumes in the comparative simulation analyses. The nominal ventilation volume is provided by the engine manufacturer. It can be seen in Figures 7-9 that with the increase of ventilation volume, the high-temperature volumes can be effectively reduced. Moreover, with the decrease of ventilation temperature, the ventilation performance can be significantly enhanced. These observations are consistent with common knowledge about the ventilation system. Hence, the present CFD calculation model and boundary settings are correct, which can be further used for control of the ventilation temperature. Figure 6: High-temperature region and air outlet-exhaust vent pressure ratio. Figure 7: _Cont_. Figure 8: High-temperature volumes above 50 and 55 \({}^{\circ}\)C, and temperature streamlines between 45 and 60 \({}^{\circ}\)C in the conditions of (**a**) ventilation temperature 40 \({}^{\circ}\)C with 0.75 nominal volume, (**b**) 40 \({}^{\circ}\)C with nominal volume, and (**c**) 40 \({}^{\circ}\)C with 1.25 nominal volume. Figure 7: High-temperature volumes above 50 and 55 \({}^{\circ}\)C, and temperature streamlines between 45 and 60 \({}^{\circ}\)C in the conditions of (**a**) ventilation temperature 45 \({}^{\circ}\)C with 0.75 nominal ventilation volume, (**b**) 45 \({}^{\circ}\)C with nominal volume, and (**c**) 45 \({}^{\circ}\)C with 1.25 nominal volume. When comparing the high-temperature volumes above 50 \({}^{\circ}\)C and 55 \({}^{\circ}\)C in Figures 7-9, it can be seen that the high temperature around the diesel engines increases sharply, especially for three parallel units on the same side. However, the overall temperature of the cabin decreases with the decrease of the settings of the ventilation temperature and volume. Table 4 shows the amount of the high-temperature volumes in Figures 7-9. As can be seen in Table 4, the ventilation temperature contributes significantly in cooling the main cabin. However, in practice one should consider the economy-to-temperature ratio. A low ventilation temperature is able to improve the cooling effect but also increases the operation cost. As a result, it is crucial to control the ventilation temperature to make a good tradeoff between in the ventilation performance and cost.