Diagnostics of Engine Noise During Run-up Using HELS Based Nearfield Acoustical Holography

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 information enables one to correlate a particular drive train order at a specific frequency and rpm to the peak amplitude of the sound pressure at a specific location on the engine surface, e.g., an oil pan. The depth and breadth of clearly defined information obtained can be very helpful to identify noise sources and how they change with the engine speed.