Thermo-acoustic performance of full engine encapsulations – A numerical, experimental and psychoacoustic study

Abstract This paper presents the development and investigation of a thermo-acoustic encapsulation for a diesel engine by means of a combined approach of thermo-acoustic recordings, numerical simulations and psychoacoustic evaluation. The encapsulation is positioned in close proximity to the engine and completely surrounds the entire engine block. Experimental tests are performed with the help of an acoustic engine test bench, where the surface of the engine is observed by infrared cameras and the sound is monitored by a microphone-array. Thermal and acoustic measurements of the engine without an encapsulation are recorded and used as reference data for simulations to evaluate and improve the functionality of different design concepts of the encapsulation in comparison to the same engine without encapsulation. The received experimental results are also used to select proper materials as well as to design the heat insulating and sound absorbing encapsulation. Based on the experimental investigations, some weak points of the first prototype are identified. These experimental findings, as well as numerical simulations of the sound radiation, are used as a basis for further design improvements to the encapsulation. The new design that is developed shows a significant improvement in the insulation of the car engine, both thermally and acoustically. In the last step, the perception of the engine sounds are evaluated by measuring changes in the perceived loudness and sound preference of the engine with and without encapsulation by human participants. This allows for a more objective evaluation of the acoustic behavior of the developed engine encapsulation.