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The fundamental effect that cycle difference of a reciprocating internal combustion engine has on noise and performance, together with noise and vibration characteristics of 2- and 4-cycle diesel engines, is described. Some of the conclusions drawn from extensive noise and vibration measurements include: 1. Variation in engine surface vibration and noise radiated is linearly related to a force input applied to the structure. 2. A method of predicting combustion noise levels of current automotive diesel engines. 3. A combination of engine performance calculations with relations for predicting overall engine noise in initial design stages.

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 general problem of estimating the noise which vibrating surfaces will produce is discussed with particular application to diesel engines and their component parts. The measurement and prediction of engine noise balances using the surface vibration technique is described and the variation of engine block vibration with engine type and speed illustrated. Some measured radiation ratio’s for engine surfaces and components are given. Finally a method for measuring surface vibration on diesel engines using a laser doppler velocimeter is described.

This paper describes the use of digital measurements to assess acoustic intensity close to the various surfaces of a two litre gasoline engine. Using phase-locked data acquisition an acoustic power balance is constructed for the engine which is shown to correlate well with three other methods - lead covering, average surface vibration level and close microphone. However, the prediction of sound pressure level from these power balances is shown to be difficult, at least at 1 m from the surface. A simple relationship between acoustic intensity and sound pressure level in the frequency domain has been found.

The paper describes an investigation to identify the sources of forces which cause the vibration of different parts of the engine structure in a turbocharged heavy duty diesel engine of 2 litres/cylinder capacity. The differences in vibration response at the main bearings and on the engine outer surfaces is shown. Results of overall dynamic stiffness measurements at the main bearings indicate that the oil film has a negligible effect on the behaviour of the major vibration response. A model is put forward for an absolute prediction of the engine outer surface vibration. The model can be seen as an alternative or complement to current F.E. techniques. A comparison between predicted and measured vibration on the crankcase is presented. Predicted vibration response spectra are used to show the relative contribution of liner and bearing forces to the overall crank-case and cylinder block vibration of the engine.