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The paper describes the assessment and testing of two high speed diesel engine structure modifications designed to reduce noise. The modifications tested are a five main bearing version of a standard three main bearing engine and the addition of a sump plate. The results indicate that it is difficult to assess the running engine vibration and noise characteristics using modal analysis techniques but that this is possible when using the banger test techniques. It is shown that noise reductions up to some 4.0 - 5.0 dBA can be achieved both on the test bed and in the vehicle application.

The paper exemplifies the necessity to quantify the various noise sources present in modern automotive engines. Results demonstrate the non-linearity problems associated with many of the non-running engine rig tests currently in use. A new technique is described for combustion induced noise simulation using hydraulic excite ion. Results obtained using this experimental method are compared with those measured on the running engine.