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TECHNICAL PAPERS

Modeling and Testing of After-Treatment Devices

[+] Author and Article Information
Sabry Allam

The Marcus Wallenberg Laboratory for Sound and Vibration Research, KTH, SE-10044 Stockholm, Sweden

Mats Åbom

The Marcus Wallenberg Laboratory for Sound and Vibration Research, KTH, SE-10044 Stockholm, Swedenmatsabom@kth.se

J. Vib. Acoust 128(3), 347-356 (Nov 10, 2005) (10 pages) doi:10.1115/1.2172262 History: Received February 28, 2005; Revised November 10, 2005

Driven by emission regulations in the US and the EU exhaust systems on new diesel engines are equipped with both a catalytic converter (CC) and a diesel particulate filter (DPF). The CC and DPF are normally placed after each other in an expansion chamber, to create a complete after-treatment device (ATD) to reduce the exhaust pollutants. The ATD unit can also affect the acoustical performance of an exhaust system. In this paper, an acoustic model of a complete ATD for a passenger car is presented. The model is made up of four basic elements: (i) straight pipes; (ii) conical inlet/outlet; (iii) CC unit, and (iv) DPF unit. For each of these elements, a two-port model is used and, with the exception of the DPF unit, known models from the literature are available. For the DPF unit, a new model suggested by the authors has been used. Using the models, the complete acoustic two-port model for the investigated ATD unit has been calculated and used to predict the sound transmission loss. The predictions have been compared to experimental data taken at cold conditions for various flow speeds and show a good agreement.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Photograph of the investigated after-treatment device (ATD) together with a drawing of the various parts: (1) flexible inlet; (2) straight pipe; (3) a diverging conical duct; (4) straight pipe; (5) straight pipe; (6) catalytic converter; (7) straight pipe; (8) diesel particulate trap; (9) straight pipe; (10) straight pipe; (11) A converging conical duct; and (12) straight pipe. Geometrical data for all the elements is given in Appendix .

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Figure 2

Approximation of a conical horn using piecewise constant area straight duct sections with constant length

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Figure 3

Cross section of a unit cell in a DPF split into five sections, each described by an acoustic two-port model. Note, the filter section (II) is actually an acoustic four-port but can be reduced to a two-port due to the hard walls in sections I and III. Typical cross dimensions for the quadratic narrow channels in section II are 1–2mm with a wall thickness of 0.3–0.5mm.

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Figure 4

Neighboring channels in a DPF unit. The flow and the acoustic waves enter the channels (1) open upstream and closed downstream, then pass through the porous walls into the channels (2) closed upstream and open downstream.

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Figure 5

Real part of the propagation constants versus normalized shear wave number (sa) for a typical DPF. No flow is assumed, and the filter data are taken from Table 2 and To=293K. °°°, Γ1; —, −Γ2 propagation constants for uncoupled waves and ◇◇◇, propagation constant from Dokumaci (18). +++, Γ3 and ---, −Γ4 propagation constants for coupled waves.

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Figure 6

Imaginary part of the propagation constants (−Γ) versus normalized shear wave number (sa) for a typical DPF. No flow is assumed, and the filter data are taken from Table 2 at To=293K. °°°, Γ1; —, Γ2 propagation constants for uncoupled waves and ◇◇◇, propagation constant from Dokumaci (18). +++, Γ3 and ---, Γ4 propagation constants for coupled waves.

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Figure 7

Transmission loss versus frequency at M=0.02 before the inlet of the DPF and Tav=775K(6). Effect of different acoustic coupling conditions at the inlet and outlet: +++, with energy losses on both sides; —, with the conservation of energy at the inlet and conservation of momentum at the outlet.

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Figure 8

Layout of the test rig for mufflers at MWL/KTH. The two-microphone technique was used for the wave decomposition and to cover the desired frequency range (30–1200Hz); 2 microphone pairs were used.

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Figure 9

Transmission loss versus frequency for the CC at M=0.01 before the inlet and T=293K. ---, simulated using Kirchhoff equation 4; —, simulated using Dokumaci (18); °°°°, measured.

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Figure 10

Transmission loss versus frequency for the CC at M=0.02 before the inlet and T=293K. ---, simulated using Kirchhoff equation 4; —, simulated using Dokumaci (18); °°°°, measured.

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Figure 11

Measured and predicted transmission loss for the DPF at M=0.01 before the inlet and T=293K. °°°°, Measured; —, predicted using theory in Sec. 22; …, predicted using modified 1D model, Sec. 24.

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Figure 12

Measured and predicted transmission loss for the DPF at M=0.02 before the inlet and T=293K. °°°°, Measured; —, predicted using theory in Sec. 22; …, predicted using modified 1D model, Sec. 24.

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Figure 13

Transmission loss versus frequency for the ATD at M=0.1 in the inlet pipe and T=293K. —, predicted, °°°°, measured.

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Figure 14

Transmission loss versus frequency for the ATD at M=0.15 in the inlet pipe and T=293K. —, predicted, °°°°, measured.

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