In this paper, was investigated the thermo-acoustic improvements that could be reached in terms of noise reduction thanks to an engine compartment encapsulation with the integration of different components such as, the air intake system. First, the design of an engine bay cover made of a double shell with an air-gap in between was illustrated. It was shown that this component supplemented with an under-shield fully closing the lower plane below the engine compartment and effectively treated in terms of absorption, was leading to strong reductions of exterior noise emissions. Emission results show a promising reduction of the CO and HC quantities on the tested diesel car. One of the reasons for such improvement is the possibility of having a much hotter catalyst in re-start condition, together with fluids temperature (in the 4C range difference after 16h). The NOx results are surprisingly slightly better than those of the baseline configuration (about 4%). The type of catalyst mounted in this is not able to reduce Nox, therefore the difference might be due to a faster heat up of the catalyst, which could lead to a different behaviour of the engine management system. The presence of the encapsulation leads to general higher temperature during driving, but none was critical for the system. Higher activities of the fan were recorded, but also spot-cooling is possible. The closure of the grill didnt provide significant differences as expected, leading to only 1C difference in the long-term range (after 16h). In a second stage, it was taken advantage of the specific design of the engine bay cover to integrate an air intake device between the two shells. The air filter box and the inlet ducts were integrated and furthermore, the duct was made of the same porous material than the one used for the lower shell. The full device could then be directly installed on the vehicle. Finally, an experimental campaign aiming at evaluating the sound field surrounding the engine compartment in hot idle condition and at the driver's position for the 3rd gear WOT condition, was carried out. The analyses of the hot idle exterior noise measurements showed that the engine encapsulation was significantly reducing the SPLs, especially in the mid and high frequencies. On the other hand, no significant differences were found for the interior WOT measurement. To conclude the study, a jury session was performed which confirmed the objective acoustics investigations. For the hot idle exterior noise condition, the encapsulation with porous intake was favoured to the encapsulation without porous intake, the latter being preferred to the original design. For the 3rd gear WOT, the test persons were not able to distinguish the differences between the different configurations.
A novel approach to intake systems using sound absorbing materials
2008
20 Seiten, 23 Bilder, 7 Quellen
Aufsatz (Konferenz)
Englisch
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