In order to ensure the full heat dissipation of heat exchangers, the opening of the grille should be large, which increases the wind drag of the whole vehicle. Most of the research on the grille only focuses on its impact on the heat dissipation of the engine compartment; there is little research on its influence on the performance of the thermal management system, because it is difficult to solve the real-time data interaction of different dimensional models. So we established the 1D and 3D strong coupling model. The biggest difference from other 1D and 3D coupling models is that we can use the interfaces reserved by the two kinds of software to realize real-time data interaction, and simultaneously analyze the 1D thermal management performance and 3D flow field and temperature field of the engine components. The coupling model is used to study three heat balance conditions. The results show that the heat-sinking capability of the cooling system is the worst under the climbing condition; and the refrigeration capacity of the air-conditioning system is the worst under the idling condition. According to the heat balance results and evaluation index priorities, we determine the simulation process. In this article, first the upper grille is gradually closed; then the flow field, temperature field and evaluation indexes are studied through the strong coupling model to obtain the analysis results of the upper grille; then based on the results, the lower grille is gradually closed, and the analysis results of the lower grille are obtained in the same way. The final simulation results show that on the premise of ensuring the performances of engine cooling system and air conditioning refrigeration system, the air drag coefficient is reduced by 17.5 counts compared with the original vehicle.

This article puts forward the concept of fast idling condition. The comparative experiments of idling and fast idling warming up engine show that: during cold start, the warm-up of fast idling condition whose maximum speed is 1350 r/min is the most fuel-efficient, fuel-saving about 4.5%, time-saving about 32.5%; at normal temperature, warming up engine of fast idling condition does not save fuel. The warm-up experiments of fast idling condition that accelerations are different in the descent phase show that when the engine is cold, the smaller the acceleration in the descent phase of fast idling condition is, the more time and fuel are saved; at normal temperature, the bigger the acceleration in the descent phase of fast idling condition is, the better the fuel economy is. Therefore, it is inferred that the engine should be warmed up under fast idling condition when the engine is cold and idling condition is used to warm up engine at normal temperature. To sum up, when the engine is cold, the engine should be warmed up under the fast idling condition whose maximum speed is 1350 r/min; at normal temperature, it should be warmed up in idling condition to save fuel.