| ACOUSTICAL CHARACTERISTICS OF THE AIR FILTER IN THE
ENGINE INTAKE AIR CLEANER |
| Jang-Hoon Kang, Jeong-Guon Ih |
| KAIST |
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| ABSTRACT |
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Linear acoustic theory is used for estimating the acoustical performance of the air cleaner box composed of the
porous filter and encasing box in the engine intake system. The pleated filter structure is modeled as coupled multiple ducts
having permeable micro-perforated walls and rectangular section, in which each duct area is assumed being homogeneous or
inhomogeneous. Mathematical models describe the sound propagation within the narrow duct considering the visco-thermal
effect at the filter pleats. For the validation, transmission loss (TL) is measured, and a change in TL spectrum is clearly
observed by including the filter into the box. It is shown that the predicted TL counting the effect of visco-thermal loss agrees
reasonably well with the experimental results. Noticeable effects of the filter on the TL are observed as highly smoothing
effect at high frequencies and enhancing the TL magnitudes at troughs and lobes at low frequencies. Comparing homogeneous
and inhomogeneous channel modelings, the latter is superior in precisely predicting the trough frequencies of TL curve, but
the former is a bit better in predicting its magnitude. Parametric study on material and shape factors reveals that the number
of pleats, length of the pleated filter, and distance between neighboring pleats are the key factors in determining the TL. It is
concluded that an air filter element that has small number of long pleats with high flow resistance would bear the best
acoustical performance among all designs. |
| Key Words:
Intake noise, Air cleaner box, Filter pleats, Micro-perforated filter, Transmission loss, Silencing |
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Corresponding Author.
Jeong-Guon Ih , Email. 
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