1. Air intake and exhaust noise reduction: the intake and exhaust air channels in the engine room are used as soundproof walls, and the silencers are set up in the inlet and exhaust air channels. There is a distance buffer in the channel, which can reduce the intensity of the sound source radiation from the engine room.
2. Control of mechanical noise: the top and surrounding walls of the machine room are covered with high absorption and sound insulation materials, which are mainly used to eliminate indoor reverberation and to reduce the sound energy density and reflection intensity in the machine room. In order to prevent the noise from radiating through the gate, fire-proof iron door is set.
3. Control smoke noise: the smoke exhaust system installed on the basis of the original primary silencer special two-stage silencer can ensure the effective control of the smoke noise of the unit. Exhaust pipe length more than 10 meters to increase the diameter of the exhaust to reduce the generator set back pressure. The above treatment can improve the noise and back pressure of the generator set. Through the noise reduction, the noise of the generator set in the engine room can meet the requirements of the users outside.
The silencer of diesel generator machine is developed according to the principle of anti-noise, anti-injection and compound anti-noise. It has the advantages of large volume, small volume, light weight, stainless steel manufacture, easy corrosion and convenient installation. The sound wave is attenuated by expanding cavity and perforated plate, and the sound becomes heat energy. The principle of which is mostly multistage throttling and lowering pressure, high pressure steam passing through a control flow in the muffler and entering the pressure relief body after a large volume diffuser. In this process, the internal energy of the airflow is partially converted into sound energy of a certain frequency, and its noise is greatly reduced. In a ejected and mixed silencing shell, 2–4 energy dissipation and sound suppression inner tanks are arranged centrally. In order to absorb the thermal expansion of the exhaust steam pipe, a double-layer acoustic mask was designed in the depressurized body to move vertically and horizontally between the inner gallbladder shells to absorb the thermal expansion of the exhaust steam pipe.
Muffler is a kind of device that prevents sound from propagating and allows airflow to pass through. It is an important measure to eliminate the dynamic noise of steam emission. To measure the quality of exhaust muffler, the following three aspects are considered:
1. The muffler’s noise quantity can meet the requirement of “hygienic Standard of noise in Industrial Enterprises”
2. Adaptive performance of muffler (I. E. wide band of low and medium frequency spectrum, high temperature and high pressure, etc.)
3. Structure and performance of muffler. (reasonable size, low cost, long life, etc.)
The exhaust muffler of diesel engine is suitable for noise attenuation on the exhaust pipe of diesel generator, and also for other exhaust systems containing a certain amount of smoke and dust.
The noise reduction principle of diesel generator muffler is as follows.
The exhaust muffler of diesel generator is mainly analyzed from three aspects: noise attenuation performance aerodynamic performance and structure performance. It should have the characteristics of higher noise attenuation wider frequency band smaller resistance loss and simple structure. The exhaust muffler of diesel generator engine is usually designed as microperforated plate impedance compound type. It has high noise suppression capacity in low, medium and high frequency, and can withstand high temperature and air impact, low resistance loss and low regenerative noise. The silencing amount can reach 20dB (A). The structure of microperforated plate impedance compound muffler is commonly used.
The theory and calculation methods of the muffler, especially the microperforated tube section, are not perfect, so the performance of the muffler can be evaluated only after the experimental measurement. The expansion ratio m (m=D2/d2) of Beijing diesel generator muffler has a great relationship with the noise attenuation, so the reasonable choice in design should be between 4 ~ 15 and 4 ~ 15. In a certain range, the larger m is, the better the silencing effect is, but m can not be too large. Otherwise, the section of the expansion chamber is too large, so that the medium and high frequency sound wave does not propagate in the form of plane wave in the muffler, but the beam wave passes through it, which leads to the decrease of the silencing volume. In the low frequency range, when the wavelength is much larger than the size of the expansion chamber, because the expansion chamber itself is equivalent to a low pass filter, it will affect the effective low frequency muffler range of the diesel generator muffler. The sound absorption coefficient and band width of perforated plate are mainly determined by perforation rate and aperture. The aperture of microperforated plate is in the range of 0.5~1mm, the perforation rate is 1 / 3% and the thickness is generally between 0.5~1mm. In order to achieve wide band and high frequency absorption, the perforation rate of the front layer near the air flow is sometimes slightly higher than that of the rear layer, and the depth of the front and rear cavity may be the same or different, but before, the ratio of the rear cavity depth should not be greater than 1:3.