Marine diesel exhaust noise 1

In order to calculate exhaust noise spectra (on e.g. bridge wings) a simple mathematical model is given of a large turbo-supercharged marine diesel engine as a source of sound, connected to an exhaust system with or without muffler.

The exhaust gas turbines are considered as high internal impedance sound sources. Spectra arc computed with the aid of the Fourier analysis of a periodical trapezium gas flow function in combination with the transfer function of the exhaust system The latter function is determined from scale models. The influences of engine power, number of cylinders, number of revolutions per minute, turbine nozzle area etc. on the sound pressure level are investigated.

Continued research is needed especially on some of the tentative conclusions which indicate for example that a factor 2 increase of the power per cylinder implies an increase of the sound pressure level by 3 dB and moreover that this level is reduced by at least 24 dB if the number of revolutions per minute of the crank-and propeller shaft is reduced by a factor 2.