The main noise sources of the diesel generator set are generated by the diesel engine, including exhaust noise, mechanical noise and combustion noise, cooling fan and exhaust noise, air intake noise, generator noise, noise generated by the transmission of foundation vibration, etc. When the diesel generator set is running, it usually produces 95 ~ 128 db(a) noise. If the necessary noise reduction measures are not taken, the noise of the unit operation will cause serious damage to the surrounding environment. In order to protect and improve environmental quality, noise must be controlled.
1. Exhaust noise. Exhaust noise is a kind of high temperature, high speed pulsating air flow noise, is the largest energy of engine noise, its noise can reach more than 100 db, is the most important part of the total engine noise. The exhaust noise generated by the generator during operation is directly discharged through the simple exhaust pipe (the original exhaust pipe of the generator set), and with the increase of the airflow speed, the noise frequency is also significantly increased, which has a serious impact on the life and work of neighboring residents.
2, mechanical noise and combustion noise. Mechanical noise is mainly caused by the vibration or mutual impact caused by the periodic changes of gas pressure and motion inertia force of the engine moving parts during operation. It has the characteristics of far noise propagation and reduced attenuation. Combustion noise is the structural vibration and noise produced by diesel oil during combustion.
3, cooling fan and exhaust noise. Fan noise is composed of eddy current noise, rotating noise and mechanical noise. Exhaust noise, airflow noise, fan noise, and mechanical noise will spread out through the exhaust channel, thereby causing noise pollution to the environment.
4. Air inlet noise. The role of the air inlet channel is to ensure the normal operation of the engine and to create good heat dissipation conditions for the unit itself. The air intake channel of the unit must be able to allow the air to enter the machine room smoothly, but at the same time, the mechanical noise and airflow noise of the unit will also radiate to the outside of the machine room through the air intake channel.
5. Transmission noise of foundation vibration. The intense mechanical vibration of the diesel engine can be transmitted over long distances through the ground and then radiated through the ground.
The principle of noise reduction in the diesel generator room is to use efficient sound absorbing materials and noise reduction devices to reduce the noise of the inlet and exhaust channels and exhaust systems under the premise of ensuring the ventilation conditions of the diesel generator set, that is, without reducing the output power, so that the noise emissions meet the national standard (85db(a)).
The most fundamental way to reduce generator noise is to start with the sound source and adopt some conventional techniques to reduce noise. Such as muffler, sound insulation, sound absorption, vibration isolation, etc., is the most effective way.
1, reduce exhaust noise. Exhaust noise is the main noise source of the unit, which is characterized by high noise level, fast exhaust speed and difficult control. The use of a special impedance compound muffler can generally reduce the exhaust noise by 40-60 db(a).
2, reduce axial fan noise. When reducing the noise of the cooling fan of the generator set, two problems must be considered, one is the pressure loss allowed by the exhaust channel. The second is the required noise reduction. In view of the above two points, a resistive plate muffler can be selected.
3. Sound insulation, sound absorption processing and vibration isolation of the unit in the machine room
(1) Sound insulation in the equipment room. After the exhaust noise and cooling fan noise of the unit are reduced, the main noise source remaining is the diesel engine mechanical noise and combustion noise. The method used is to remove the remaining Windows in addition to the necessary internal wall observation window connected with the observation chamber, all holes and holes should be tightly sealed, and the sound insulation quantity of the brick wall is required to be more than 40 db(a). The doors and Windows of the equipment room are fireproof and sound-proof.
(2), air intake and exhaust. After sound insulation in the equipment room, solve the ventilation and heat dissipation problem in the equipment room. The air intake should be set in the same straight line with the generator set and the exhaust. The air inlet should be equipped with a resistant plate muffler, because the pressure loss of the air inlet is also within the allowable range, the air volume in and out of the machine room can be naturally balanced, and the ventilation and heat dissipation effect is obvious.
(3) Sound absorption treatment. The five walls in the machine room except the ground can be used for sound absorption, and the perforated plate resonance sound absorption structure is adopted according to the spectrum characteristics of the generator set.
(4) The indoor air exchange, the good sound insulation of the machine room, will make the closed water-cooled generator when the room is shut down, the air in the room can not be convection, the high temperature in the room can not be timely down, can use low noise axial flow fan, and equipped with a resistance sheet muffler can solve the problem.
(5) Unit vibration isolation. Before the installation of the generator set, vibration isolation treatment should be carried out strictly according to the relevant information provided by the manufacturer to avoid the long-distance transmission of structural sound, and the air sound is constantly radiated in the transmission, which can not make the factory boundary noise level reach the standard. For the existing generator set that is required to be treated because of exceeding the standard, the vibration of the ground near the unit must be measured, and if the vibration is obvious, the vibration isolation treatment of the generator set must be performed first.
After effectively reducing the noise, in order to make the environment of the machine room more beautiful and practical, usually the sound absorption layer of the wall and the ceiling is also decorated with microporous aluminum plastic punching board, and the lighting system is reasonably configured.