VTT Technical Research Centre of Finland
A night time noise complaint was issued from the residential area near one of Wärtsilä’s main large 4-stroke medium speed engine factories located in downtown Vaasa. This factory produces the Wärtsilä 32 ship engine which provides higher unit power, enhanced fuel consumption, significantly reduced componentry and integral computer control to a fiercely competitive sector of the engine business. The Wärtsilä facility produces about 500 engines per year and every engine is subjected to a test run. An investigation found that the likely source of the intolerable noise was from the exhaust from a W6L32E engine 1000 hour endurance test which was running continuously at 750 rpm and full load.
Challenge:An environmental noise study was conducted in the middle of the night when the test engine was running, with measurements taken at three locations between the test facility and the nearby residential area. Sound pressure level measurements indicated a peak in the sound spectrum at the 100 Hz 1/3 octave band at approximately 94 Hz in narrowband, which corresponds to the crankshaft rotation frequency (CRF) order of 7.5. Typically the exhaust noise of the W6L32E engine should have the highest peaks at CRF orders 3 and 4.5. The measured noise was found to be well under the nighttime environmental noise limit. The annoyance levels were presumed to be high because of the dominant half order modulated low frequency noise components.