Study On Multifield Coupling Heat Dissipation Mechanism And Structure Optimization In Engine Compartment Of A Passenger Vehicle

With the popularization of high output engine,the thermal load of engine compartment was increasing gradually.At the same time,many new technologies and new functions were constantly upgraded,and new components which carrying these technologies and functions were installed in the engine compartment.This situation made the engine compartment crowded and the heat dissipation problem became increasingly severe.The researchs on heat dissipation of engine compartment were mostly carried out from the perspective of flow field or temperature field,and few scholars forced on the influence of vibration,thermal radiation electromagnetic field and temperature difference field on heat dissipation performance of engine compartment.In this dissertation,the engine compartment of a passenger vehicle equipped with turbocharged engine was taken as the research object,and the multifield coupling heat dissipation principle and structure optimization were studied,which had reference significance to explore the solutions of complicated heat dissipation problems of passenger vehicles.This research is mainly carried out from the following aspects:1.Problem identification and cause analysis of heat dissipation problems.Based on the research on the structural characteristics of the engine compartment,environmental chamber experiments under various conditions were carried out.The heat dissipation problems and the worst conditions were confirmed based on the experimental results.According to the experiments,the simulation model was established,and the reasons of heat dissipation problems were analyzed from the perspective of flow field and temperature field,respectively.2.Study on the mechanism of enhanced heat dissipation in engine compartment.The engine compartment was divided into radiator working area and engine working area.To improve the heat dissipation performance of the radiator,the ’same direction’ principle of heat exchanges was proposed based on the field synergy theory of heat exchanger.This principle provided a theoretical basis for reasonable matching between upstream and downstream heat exchangers.Vibration enhanced heat transfer mechanism for radiator was carried out from the angle of the field synergy.The mechanism reveals that the flow field near the tube and fin is disturbed by vibration,making the field synergy angle deviate from 90°,thus the heat transfer coefficient is improved.Aiming at the excessive temperature of the transmission shaft sheath in engine working area,corresponding solutions were proposed from the angle of field coupling between thermal radiation electromagnetic field,flow field and temperature field.The solutions reduce the convective heat dissipation resistance and increase the thermal resistance in the process of radiation heat transfer.3.Study on design and optimization of multi-field coupling structures.Firstly,the enhanced heat dissipation structures of the radiator and engine work areas were designed based on the mechanisms of enhanced heat dissipation.Secondly,orthogonal test and variance analysis were adopted and the key structures that had significant influence on the optimization goals were identified.Radial basis neural network(RBFNN)was adopted to establish the prediction model between the optimization objective and structure parameters.Finally,particle swarm optimization algorithm(PSO)was used to determine the optimal combination of structural parameters and the corresponding optimal values.4.Simulation and experimental verification.The simulation results showed that the optimized solutions improved the air leakage state,increased the radiation resistance and improved the field synergy state of the radiator and engine working areas.The simulation results of engine outlet water temperature and the shaft sheathed temperature were reduced to 104.5℃ and 118.7℃,respectively,which satisfied the requirements.Finally,the environmental chamber experiment was carried out.The engine water temperature and the transmission shaft sheath temperature were stable at about 102℃ and 115.5℃ when the experiment entered the driving balance stage,both lower than their temperature limits.The experimental result shows that the structure design and optimization based on the multi-field coupling heat dissipation mechanism could effectively improve the heat dissipation performance of the engine compartment.Figure[92]Table[21]Reference[208]...