Acoustic Analysis of Charge Air Coolers

This paper presents the results from a study of the acoustic properties of charge air coolers for passenger cars. Charge air coolers are used on turbo charged engines to increase the overall performance. The cooling of the charged air results in higher density and thus volumetric efficiency. Important for petrol engines is also that the knock margin increases with reduced charge air temperature. A property that is still not very well investigated is the sound transmission through charge air coolers. The pressure drop in the narrow cooling tubes results in frequency dependent resistive effects on the transmitted sound that is non negligible. Since the cross dimensions of the connecting tanks, located on each side of the cooling tubes, are big compared to the wave length for engine breathing noise, three dimensional effects can also be of importance. In this study an acoustic two-port for sound propagation in narrow tubes, including the effect of viscous and thermal boundary layers, is combined with three dimensional acoustic finite element modeling to represent a complete air-to-air charge air cooler. From this a linear frequency domain model for the entire charge air cooler is extracted in the form of a two-port. The frequency dependent transmission loss is calculated and compared with corresponding experimental data. Finally, there is a discussion of the results and on how the acoustic response of charge air coolers could be modified.