Prediction of Transient Engine Compartment Temperature During After-Boil

The performance of ground vehicles of all types is influenced by the cooling and ventilation of the engine compartment. An increased heat load into the engine compartment occurs after engine shut down. Heat is transferred from the hot components within the engine compartment by natural convection to the surrounding air and by radiation to the adjacent surfaces. The heat is then dissipated to the ambient mostly by convection from the exterior surfaces. The objective of this study is to develop a Computational Fluid Dynamics (CFD) simulation methodology to predict the airflow velocity and temperature distributions within the engine compartment, as well as the surface temperature of critical engine components during the after-boil condition. This study was conducted using a full-scale, simplified engine compartment of an armored combat vehicle. Steady-state simulation was performed first to predict the condition prior to engine shut down. A transient simulation followed to predict the flow and temperature fields during the after-boil. During after-boil, the stored energy from the engine, transmission, oil pan, and exhaust system start to transfer to the air in the engine compartment by natural convection. This causes a temporary rise in air temperature of the engine compartment environment, which could damage thermally sensitive components by approaching their critical design temperature and causes more heat transfer to adjacent surfaces and structures. The engine compartment air temperature starts to drop following the temporary rise until temperature equilibrium is reached. A significant advantage of this analytical methodology is that no physical test setup is required. The methodology can similarly be applied to passenger cars, light trucks, heavy trucks, combat vehicles, and other off-highway vehicles.