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This paper describes the diagnostics of noise sources and characteristics of a full-size gasoline engine during its run-up using Helmholtz Equation Least Squares (HELS) method based nearfield acoustical holography (NAH). The acoustic pressures are measured using an array of 56 microphones conformal to the contours of engine surfaces at very close range. Measurements are collected near the oil pan, front and intake sides. The data thus collected are taken as input to HELS program, and the acoustic pressure mappings on the oil pan, front and intake surfaces are calculated. These reconstructed acoustic quantities clearly demonstrate the “hot spots” of sound pressures generated by this gasoline engine during its run-up and under a constant speed condition. These acoustic pressure mappings together with order-tracking spectrograms allow for identification of the peak amplitudes of acoustic pressures on a targeted surface as a function of the frequency and engine rpm.

This paper describes a method of noise diagnostics by visualizing sound at its source and as it propagates through a complex structure. The underlying principle of this approach is the Helmholtz equation least squares (HELS) method which has been proven theoretically and experimentally to be a robust tool for reconstructing acoustic radiation from an arbitrary object. Examples of using HELS to pinpoint the noise source locations and their transmission paths are demonstrated. The depth, breadth, and clarity of the information retrieved can be very helpful to a practicing engineer who is challenged to recommend abate noise problems cost effectively.