Research Papers

Acoustic Source Characterization for Prediction of Medium Speed Diesel Engine Exhaust Noise

[+] Author and Article Information
Antti Hynninen

Senior Scientist
VTT Technical Research Centre of Finland,
P.O. Box 1000,
FI-02044 VTT, Finland
e-mail: antti.hynninen@vtt.fi

Mats Åbom

KTH Competence Center for Gas Exchange,
Marcus Wallenberg Laboratory,
Stockholm SE-10044, Sweden
e-mail: matsabom@kth.se

1Corresponding author.

Contributed by the Noise Control and Acoustics Division of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received April 26, 2013; final manuscript received November 15, 2013; published online December 24, 2013. Assoc. Editor: Lonny Thompson.

J. Vib. Acoust 136(2), 021008 (Dec 24, 2013) (8 pages) Paper No: VIB-13-1134; doi: 10.1115/1.4026138 History: Received April 26, 2013; Revised November 15, 2013

To achieve reliable results when simulating the acoustics of the internal combustion engine (IC-engine) exhaust system and its components, the source characteristics of the engine must be known. In the low frequency range only plane waves propagate and then one-port source data can be determined using, for example, the acoustic multiload method. For the medium speed IC-engines used in power plants and ships, the exhaust duct noise often needs to be analyzed up to 10 kHz, i.e., far beyond the plane wave range, and it is then more appropriate to use acoustic power to characterize the source. This power should ideally be measured under reflection-free conditions in the exhaust duct. The results from an earlier study showed that a suitable way to characterize the source for any frequency is to determine the in-duct sound power by extending the plane wave formulation with frequency band power weighting factors. The aim of this study is to apply this high frequency range method in situ to a real test engine. Another aim is to define, theoretically, how to combine the source data in the low frequency plane wave range with those in the high frequency nonplane wave range using a source sound power formulation.

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Fig. 1

Schematic of the acoustic one-port source and the propagating waves. In the low frequency plane wave range the downstream (+) and upstream (−) propagating waves can be separated using the two-microphone method.

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Fig. 2

Directions of the sound power flow in an acoustic two-port. The power is positive when flowing out of the port.

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Fig. 3

The test engine, Wärtsilä Vasa 4R32, in the VTT engine laboratory

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Fig. 4

Pressure transducer configuration used in the exhaust pipe after the turbocharger. The axial and circumferential configurations consist of transducers 2-5-6 and 1-2-3-4, respectively.

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Fig. 5

The measured phase shift between the opposite microphones, one-three above and two-four below. The phase of microphones 1-3 and 2-4 turns from in-phase to out-phase (arg(H) ≈ π rad) at frequencies of 568.5 Hz and 578.3 Hz, respectively. Using these measured cut-on frequencies, the speed of sound can be determined.

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Fig. 6

Measured 1/3 octave frequency band sound power levels for the full engine load derived using different microphone configurations. For clarity, the frequency range weighting factors ε = 0 dB were used.

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Fig. 7

The combined outgoing sound power level of the studied diesel engine for the full engine load. The low frequency range source power is based on the multiload method. In the high frequency range, the axial pressure transducer configuration and cross-spectra averaging were used with the power weighting factors listed in Table 2.




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