TS-97
Study on Noise Reduction of Large Diesel Main Engine
Kunihiko ISHIHARA*, Makoto AOKI*
Yasushi HIRAKATA**, Eiichi SHIRAI**
ABSTRACT
In general, a diesel engine for marines generates a high level noise and it is desired to decrease the noise in order to make comfortable environment.
Then, the test of noise reduction was carried out on a large diesel main engine for marine use equipped with two turbochargers (type NA70/T09).
In this paper, the noise source is specified by noise measurement at first. Second, the noise reduction by means of the lagging is predictable and a result of this countermeasure is described. The noise reduction equipment with the resonator is also applied to the turbocharger and its result is described too.
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.
Key words: Diesel Engine, Environmental Conservation, Noise Reduction, Lagging, Resonator
1. INTRODUCTION
In a large ship like VLCC, a diesel engine has been used as a main engine in almost all ships. The reason is that a diesel engine has advantages such as high power, low fuel cost , and low maintenance cost. However, the engine generates a high level noise and it has a problem from a point of view of environmental conservation as compared with gas turbines and steam turbines. Then it has been desired to decrease the noise level moreover.
In general, the noise level of the large diesel engine is higher than 110dB(A) at 1m apart from the engine and it has been becoming problems such as the operation error because of being hard to communicate and the low efficiency of work due to the human fatigue.
According to the regulation for keeping of hearing, the permissible noise exposure time is less than 30 minutes under 110dB(A) at 1000HZ the noise level e.g. This means that they can't work at all under the environment.
In this paper, the study of the noise reduction effect of the conventional techniques such as lagging and using resonator was carried out on the subject of a large diesel engine (10L80MC) with two NA70/T09 type turbochargers.
As a result, the suppression effects were 10dB by the lagging and were 6dB by the resonator. In this paper, finding the noise source by measurement, predicting the reduction effect of countermeasures such as lagging and resonator and measuring them are described.
2. NOISE MEASUREMENT AND SEARCH OF SOURCE POSITION
Fig. 1 shows a general construction of the large diesel engine studied here and noise measuring positions (A-C). The value (Before Countermeasure) at each measuring position shown in this figure is the noise level before performing a countermeasure. And Fig. 2 shows the spectrum of noise at position A. Same spectra are also obtained at other measuring positions. The frequency component 1500Hz seems to be dominant from Fig. 2. This is the frequency associated with the rotating speed of the turbocharger (9825rpm) and the number of the impeller (9). That is to say,
F =NZ/60 = 9825×9/60 = 1475Hz (1)
Fig. 2 shows that the noise source governing the total noise is the aerodynamic noise generating from the impeller and it propagates in the scavenging air receiver and radiates from the engine.
