Fig. 8 shows the reduction effect of three resonators. The abscissa axis is the rotating speed of turbocharger. Results of two measuring points are showed in this figure. The resonant frequency appears around 10000〜12000rpm and this is close to the designed value. The reduction effects of each resonator are shown in Table 2.
Table2 shows that the reduction effect of 5〜8dB is obtained in all frequencies in case2, the effect of 4〜7dB is obtained around 11300rpm which is design value in case 3 and the effect of 4〜7dB is obtained in wide frequency range in case4.
A large perforated ratio gives a much reduction effect which appears only at resonant frequency in case of no absorbed material in the space.
5. CONCLUSION
A large diesel engine has advantages such as high power, low fuel cost and low maintenance cost. And it will have been used from now on. It is inevitable subject to suppress the noise in order to improve the environmental conservation.
In this paper, the conventional techniques of noise reduction were applied to the large diesel engine and the effect was evaluated. As a result, it is clarified that the reduction of 10dB by the lagging and 6dB by the resonator can be obtained in the actual engine.
There is no room for doubt that more reduction is required and it will be desired to develop the noise reduction equipment with the new concept and the drastic effect.
References
[1] T. Hukuda, T. Tanaka, 'Outline of Large Marine Diesel Engines'. JSAE. Vol.53, No.10, (1999), p17 (in Japanese)
[2] Editing of Ministry of International Trade and Industry, Prevention Technique and Law and Regulations of Public Harm, (1987), p42 (in Japanese)
[3] TL Data of Lagging (offer of NICHIAS) (in Japanese)
[4] Editing of JAMS, Architectural Acoustic Book, (1963), p24 (in Japanese)
