Noise control of diesel generator set

Telecommunication enterprises in modern cities must be foolproof because of the characteristics of their own industries. In order to ensure uninterrupted operation of communications equipment such as switches, the general use of diesel generators as a standby power of their own, once the commercial power failures, immediately start the diesel generator, the electric machine conversion / oil screen (ATS) is switched by a diesel generator group of communication equipment to provide power to the normal operation protection of telecommunications services.

As most of the telephone stations are located in densely populated areas, the environmental requirements are very high in these areas, and the noise of diesel generator sets is often the main source of noise in the surrounding environment. The current society for environmental protection have become increasingly demanding, how to control the noise pollution effectively is a difficult, but also has great popularization value, and this is our main job of communication construction, should get more attention. In order to do the work well, first of all, we should understand and analyze the noise composition of diesel generator set.

1 source analysis

Diesel engine noise is a complex sound source composed of many kinds of sound sources. According to noise radiation mode, diesel noise can be divided into aerodynamic noise and surface radiation noise. According to the mechanism, diesel engine surface radiation noise can be divided into combustion noise and mechanical noise. Among them, aerodynamic noise is the main noise source.

1.1 aerodynamic noise

Aerodynamic noise is due to the unsteady process of gases, that is, the perturbation of gases and the interaction of gases with objects. The aerodynamic noise radiated directly from the atmosphere includes intake noise, exhaust noise, and cooling fan noise.

1.1.1 intake noise

Intake noise is one of the main aerodynamic noise of diesel engine. It is formed by the fluctuation of pressure fluctuation caused by the periodic opening and closing of the intake valve. When the intake valve opens, a pressure pulse is generated in the intake pipe, which is damped as the piston continues to move; a pressure pulse with a certain duration is also produced when the inlet valve closes. A periodic intake noise is thus generated. The noise frequency components are mainly concentrated in the low frequency range below 200Hz. At the same time, when the high speed airflow to flow through the flow area of the inlet valve when the turbulence caused by the body, lead to high frequency noise, the flow area of the inlet valve is constantly changing, so the turbulent noise has a certain frequency range, high frequency range mainly concentrated in more than 1000Hz. When the natural frequency of the air inlet column is consistent with the main frequency of the periodic intake noise, the resonance noise of the air cylinder will be more prominent in the intake noise.

For turbocharged engines, the intake noise is higher than that of the non turbocharged engine because of the higher speed of the turbocharger. The turbocharger noise is due to turbulence noise periodically cutting blade rotation noise produced by air and formed by high speed airflow, is a continuous high frequency noise, mainly distributed in the frequency range of 500~10000Hz. At present, most of our companies use turbocharged engines.

The intake, intake noise and engine inlet valve structure, cylinder diameter, cam profile design factors. For the same engine, the influence of the speed is the biggest, and the increase of the speed can lead to the intake noise increasing by 10~l5dB (A).

1.1.2 exhaust noise

Exhaust noise is the most important noise source in engine noise, and its noise is generally higher than the engine noise by 10~15dB (A). Engine exhaust is high temperature (800~l000 degrees Celsius), high pressure (3~4 atmospheric pressure) gas. The exhaust process is generally divided into two stages, namely the free exhaust stage and the forced exhaust stage. Engine exhaust gas is rushed out of the exhaust valve, enters the muffler along the exhaust manifold, and is finally discharged from the tailpipe into the atmosphere. In this process, a wide range of exhaust noise is generated.

The exhaust noise contains complex noise components: per unit time as the number of exhaust pipe and the exhaust noise, the fundamental resonance noise of the gas column, the exhaust manifold air blowing noise, exhaust gas jetting and impact noise, the Helmholtz resonance noise of the cylinder, Carmen eddy noise and the turbulent noise inside the exhaust system.

The main factors that affect engine exhaust noise are cylinder pressure, exhaust valve diameter, engine displacement and exhaust valve opening characteristics. For the same engine, the engine speed and load are the most important factors affecting the exhaust noise.

1.1.3 cooling fan noise

Fan noise consists of rotating noise and turbulent noise. The rotation noise is caused by the pressure pulsation of the air due to the periodic cutting of air by the blades of the fan, and the blade passing frequency is the fundamental frequency and is accompanied by higher harmonics. The noise is due to turbulence caused by the motion of the fan air turbulence around the air disturbance, detached, forming gas compression and thinning process and the formation of a wide band noise.

The noise of cooling fan is affected by the speed of rotation, and the speed is doubled, which leads to the increase of sound level 10~15dB (A). At low speeds, fan noise is much lower than engine noise, and at high speeds it tends to be the dominant source of noise. At present our company uses the diesel engine speed to be more than 1500 revolutions / minutes, belongs to the high speed engine.

1.2 surface radiation noise

Combustion noise and mechanical noise are hard to distinguish. They usually vibrate through a cylinder due to pressure generated by combustion in the cylinder