Thermal Management Analysis And Multi-objective Collaborative Optimization Of Engine Compartment Based On High-efficiency And High-precision Co-simulation

The popularization of the high-power-density engine and the installation of a multi-function control system make the heat dissipation of the compact under-hood compartment more difficult.Unreasonable structural design and unsmooth airflow flow in the under-hood compartment will lead to insufficient heat dissipation or excessive cooling of engine cooling module s and engine room parts,which seriously affects the safety,economy,and emission of the vehicles.Therefore,the issue of under-hood thermal management has been paid more a nd more attention by vehicle manufacturers.At present,the simulation analysis of under-hood thermal management still has certain limitations in engineering applications due to the joint constraints of calculation accuracy and cost.In this paper,the heat damage risk and overcooling problem exposed by an MPV in the thermal balance test of an environmental chamber was taken as the research object.The one-dimensional and three-dimensional co-simulation of the heat dissipation performance of the engine cool ing module,the direct and indirect co-simulation of the heat transfer performance of the cabin components,and the multi-objective optimization of the heat dissipation performance engine room based on the co-simulation strategy were carried out.The specific contents are as follows:(1)The vehicle thermal balance test of a n MPV with high speed,6% climbing,and 10% climbing was carried out in the environmental warehouse.The results show that 10 % climbing is the worst heat dissipation condition.The in let air temperature of the engine exceeds the control limit of 2.5°C,and the outlet water temperature of the engine is lower than the control limit of 6.5°C,which exposes the insufficient heat dissipation of the intercooler and the excessive heat dissipati on of the radiator.Moreover,the wall temperature of the oil pan and other components exceeds the tolerance limit of 6.3～9.4°C,while the wall temperature of the battery and other components is lower than the tolerance limit of 8.2 ～35.5°C,indicating that there were thermal hazard risks and overcooling phenomenon.(2)A one-dimensional and three-dimensional co-simulation strategy was proposed.The inlet air velocity of the cooling module obtained by the three-dimensional vehicle model was transformed into the pressure loss coefficient,which was applied to the corresponding one-dimensional model as a boundary to analyze the heat dissipation performance of the cooling module.Compared with the one-dimensional method,the calculation speed and temperature acc uracy of the one-dimensional and three-dimensional co-simulation method can be improved by89.9 % and 6.6 %,respectively.Compared with the three-dimensional method,the calculation cost of the one-dimensional and three-dimensional co-simulation method is saved by nearly 38.9 %,and the calculation accuracy is only about 3.0 %.This co-simulation method can balance the calculation accuracy and efficiency.(3)Through co-simulation analysis,it was found that the insufficient heat dissipation of the intercooler and the excessive heat dissipation of the radiator were caused by the serious air leakage around the intercooler and the excessive cooling inlet air flow of the radiator.In this regard,the optimized design schemes were proposed to block the air leakage path and reduce the fan speed from 2800 rpm to2600rpm.At the same time,based on the enhanced heat dissipation coupling mode in which the symmetrical arrangement of the airflow velocity field at the inlet of the cooling module and the temperature fiel d of the cold and hot fluid "small and large" or "large and small",the driving fan was guided to move 14 mm to the heat flow end of the radiator,and the air door was set on the left and right ends of the windshield.The co-simulation results showed that the inlet air temperature of the engine after the implementation of the optimization scheme decrease d by 3.4°C,and the optimized outlet water temperature of the engine increased by 2.6°C,which effectively solve d the insufficient heat dissipation and exce ssive heat dissipation in the engine cooling module.Moreover,the experimental results were basically consistent with the simulation results,and the maximum error was only 3.8 %.(4)A direct and indirect co-simulation strategy was proposed.The wall temperature of the exhaust system obtained by the direct coupling model was transferred to the corresponding indirect coupling model as the heat source boundary to analyze the heat transfer performance of the surrounding components.The comparison between temperature simulation results and experimental results show ed that the maximum error of calculating the wall temperature of the engine compartment heat source by the direct and indirect co-simulation method was 8.3%,and the maximum error of calculating the wall temperature of the surrounding components of the heat source was within 3.3%.It was verified that this co-simulation method could be used to analyze the heat transfer performance of components around the heat source of engine room.(5)Through co-simulation analysis,it was found that the problem of overheating and overcooling of engine compartment components was caused by the high thermal radiation intensity of the exhaust pipe and the large cooling inlet flow of the engine room.In this regard,based on the field synergy principle of convective heat transfer enhancement of high-temperature components,the diversion angle of the lower guard plate of the engine room was designed to be 15°,by reducing the synergy angle between the surrounding air velocity vector and the temperature gradient vector.And put forward the optimization design scheme s such as reducing the driving fan speed by 200 rpm.The co-simulation results showed that the temperature of the optimized oil pan and other overheated components dropped by 11.9～20.5°C,and the temperature of the optimized battery and other overcooled parts increased by3.6～5.5°C,which effectively solved the problems of overheating and overcooling around the heat source in the engine compartment.The experimental results were in good agreement with the simulation results,and the maximum error was within 3.3%,which verified the reliability of the simulation results and the effectiveness of the optimal design scheme.(6)A multi-software automatic co-simulation strategy was proposed,which integrated the mesh deformation model,the three-dimensional vehicle CFD model and the one-dimensional engine cooling module heat dissipation model.Combined with the quadratic response surface surrogate model and the non-dominated sorting genetic algorithm-II,the multi-objective optimization of the inlet air temperature of the engine,the outlet water temperature of the engine,and the cooling drag was carried out.The multi-criteria decision-making grey correlation analysis method was used to select the reasonable optimal solution from the Pareto solution set,and the maximum error with the detailed model solution was controlled within 1.5%.After multi-objective optimization,the inlet air temperature of the engine decreased by2.9°C,the outlet water temperature of the engine increased by 6.7°C,and the cooling drag coefficient decreased by 17.5%.It effectively solved the problem that it was difficult to balance the heat dissipation of engine cooling module and the cooling drag of engine compartment.