Acoustic performance of a heat exchange silencer for marine diesel engine

Abstract

For the noise contribution of a marine diesel engine, exhaust noise plays an important role, especially considering its low frequency characteristics. The marine exhaust silencer is an effective device to attenuate the engine exhaust noise. Expansion chamber or resonators have been the backbone of almost all marine exhaust silencers, but issue of bulkiness remains. It is well known that the passband for an expansion chamber is related to its geometric length. For a fixed firing frequency, if the exhaust gas is cooled, then the wavelength of the firing frequency can be reduced. Inspired by this principle, the heat exchanger and silencer are combined to improve the low frequency effect of the device. Various reactive configurations are tried to get a well-balanced silencing effect. The effectiveness-number of transfer unit method and acoustic finite element method are adopted to calculate the noise reduction effect with or without exhaust gas cooling. It is concluded that that the heat exchange silencer has satisfactory cooling effect on the exhaust gas, but its contribution to noise attenuation is very limited. Since the reduction of the exhaust gas temperature, low-frequency performance of the silencer is enhanced.