Medium Speed Diesel Engine Noise

The paper briefly reviews past work on diesel engine noise with particular reference to medium speed engines. A survey carried out on a large number of British and European turbocharged and water-cooled dieseis having bores in the range 2 3/4 in to 33 in (∼ 70 mm to 840 mm) clearly indicated at least two main sources. A qualitative analysis of the problem suggested these to be due to combustion and piston transverse motion in the liner clearance space. None of the engines examined had an International Standards Organization rating lower than Noise Rating 85. A comparison of theoretical trends with those obtained from the survey proved encouraging and application of the analytical findings to five specific engines having bores of 5 in, 8 in, 10 1/4 in, 12 1/2 in and 14 1/4 in (∼ 127 mm, 200 mm, 260 mm, 320 mm and 360 mm) yielded reasonable estimates of the overall noise, but poor approximations to the relevant frequency spectra. Much more work on the effects of crankcase attenuation would appear in order. It is concluded that the wider acceptance of medium speed dieseis will not lead to increased noise problems provided appropriate action is taken at the design stage. Broad design recommendations are presented and the causes of variations of noise with time and of engine to engine scatter discussed. The marked improvements obtained on a 14 1/4 in (∼ 360 mm) bore engine are shown.