Study of Hot Air Recirculation in Engine Compartment of a Newly Developed Sport Utility Vehicle

<div>During idling tests of a newly developed sport utility vehicle (SUV) under tropical high-temperature conditions, the condenser surface temperature exceeded the allowable range, degrading the air-conditioning system’s cooling performance. In this study, a three-dimensional computational fluid dynamics (CFD) model of the engine compartment flow field was established using STAR-CCM+. The results reveal that under idling conditions, the kinetic energy of hot air passing through the cooling module was insufficient to overcome the pressure difference between the front and rear sections, thus inducing hot air recirculation (HAR) and increasing the overall compartment temperature. To address the unfavorable flow field characteristics, four structural improvements were proposed and simulated for both flow and temperature fields. Through comparative analysis, the optimal scheme was determined: installing a flow guide baffle above the engine. Simulation results show that the airflow velocity above and below the engine increased by 54% and 71%, respectively, and HAR was effectively suppressed. The optimal scheme was further validated under real-vehicle idle conditions, and the temperature deviation between simulation and measurement was within 2%, confirming the reliability of the numerical model. In addition, the optimized scheme was verified under three typical harsh driving conditions, including hill climbing, high-speed climbing, and high-speed driving. Both simulation and test results indicate that the scheme significantly enhances airflow velocity in the engine compartment, with temperature errors maintained within 5%. The present study effectively mitigates the compartment temperature rise caused by HAR, and the proposed baffle scheme provides a feasible solution for the thermal management design of new SUVs under both idle and severe driving conditions.</div>