High performance engines required in contemporary vehicles are causing underhood components to operate under hostile temperature environments. Aerodynamic styling and the addition of new components to the engine compartment further add to the problem by decreasing the volume of underhood cooling air flow. The addition of engine compartment coverings required to meet environmental noise reduction standards further restrict and debilitate air flow cooling.
The above conditions demand that the analysis of air flow patterns and heat transfer phenomena under the hood be an essential part of early systems design of new engines, engine compartment components, and underhood component packaging. A numerical approach to calculate cooling air flow velocity and temperature distribution of the air and engine compartment components is utilized.
Air flow is calculated using a finite volume Computational Fluid Dynamics code on a 220,000 cell representation of the flow domain. A three dimensional Navier-Stokes Equation solver with a “k-epsilon” turbulence model is used to calculate the flow field and convective heat transfer coefficients. Inlet boundary conditions for the code are provided using Laser Doppler Velocimetry measurements performed in the Pininfarina wind tunnel. Results of the code are mapped to a super block lumped mass representation of the underhood environment. The three modes of heat transfer (convection, conduction, and radiation) are modeled using a lumped parameter resistor-capacitor solver.
The application of the above method to the 1993 Opel Vectra equipped with a newly-developed V6 engine is presented. Areas of restricted air flow and high underhood component temperature were identified. Trade-off studies of several insulation and/or shielding strategies were performed to create a cooler environment for the operation of thermally sensitive components under severe operating conditions. The tool can be used to optimize operating parameters of new engines and packaging strategies under the hood to reduce potential thermally induced problems.