Diesel generator set noise treatment

Diesel generator set noise treatment

Diesel generator set, as the backup power supply of municipal electricity, is the necessary emergency equipment for post and telecommunications, medical treatment, hotel and other departments. In many places where electricity supply is not normal or cannot be reached, diesel generator sets are essential equipment. However, while the diesel generator sets bring people convenient electricity, their strong noise also brings serious noise pollution. With the increasing attention of the masses to the environmental protection problem, the national noise control laws and regulations are increasingly strict, the design of low noise units has become an urgent issue of widespread concern.

1. Basic method of noise reduction

In general, there are three basic methods of noise control: one is to reduce the noise of the noise source; The second is to isolate the noise source from the outside world by means of propagation; 3 it is to cover sound-absorbing material on air pipeline and metope and ceiling. The fourth is to protect the receiver of noise (earplugs, earmuffs).

In the design of low noise unit, in addition to reducing the sound source noise, the main means of noise reduction are sound insulation and sound absorption. The following combined with the design scheme, the sound insulation and sound absorption noise reduction methods are introduced.

Acoustic noise reduction

In the design of low noise unit, in order to isolate the noise source from the outside world, the sound insulation cover should be installed outside the unit as a barrier to prevent

Radiation of noise.

The muffler reduces the noise

In the diesel generator set, the main source of noise is the diesel engine. The noise of diesel engine mainly comes from the exhaust noise, so it is an effective way to reduce the noise of diesel engine unit to install the muffler on the intake and exhaust pipe.

Exhaust muffler has three main structures: resistance, resistance and impedance compound muffler.

In the resistive muffler, when the noise sound wave passes through the muffler channel, the sound absorbing material converts the sound energy into heat energy and plays the role of noise muffler. The performance of the resistive muffler depends on the performance of the sound absorbing material. The noise frequency of diesel engine is mainly distributed in the low and middle frequency region, especially the highest noise value in the low frequency region. The general sound absorption material in the low frequency sound absorption coefficient is very small, the sound absorption performance is poor, so it is not suitable to use the resistive muffler as the exhaust muffler of diesel engine. It is especially suitable for reducing intake noise of turbocharged diesel engines because of its good noise reduction effect in medium and high frequency.

The resistant muffler is designed according to the filtering principle of sound wave, and its performance mainly depends on the geometry size and shape. It consists of an expansion chamber

Or a resonant cavity properly combined with a number of tubes of limited length, taking advantage of sudden changes in the section of the pipe to propagate certain frequencies along the pipe

Or the frequency band noise is partially reflected back, so that part of the noise cannot pass through the muffler. Resistant muffler is mainly used to reduce low and medium frequency noise. 

The main noise of diesel engine is distributed in the middle and low frequency area, so it is reasonable to choose the resistant muffler.

Impedance compound muffler is a comprehensive resistance and resistance of different characteristics, can be in a wider frequency range has a good silencing effect.

Design scheme and measures of low noise unit

l Ventilation measures for units

In order to ensure the normal operation of the unit, in the structure of the unit, we should consider the heat dissipation in the machine room and the supplement of fresh air. It is required that there should be certain ventilation and heat dissipation measures in the unit, and the following two schemes can be adopted.

Scheme 1: The blast of the diesel engine cooling fan blows away the heat of the generator set and sucks in fresh air. The louver type air inlet shall be installed on the sound insulation cover. (See 4 Ventilation Noise Reduction Diagram for details)

Scheme 2: the ventilation fan is installed on the sound insulation cover. At the same time, it is better to set the air inlet near the generator fan. The air intake of the ventilator fan and the air inlet should meet the requirements of the exhaust air of the diesel engine. (See 4 Ventilation Noise Reduction Diagram for details)

The air inlet is set on the sound insulation cover, and the following problems should be paid attention to:

1) The air intake of the air inlet should meet the requirements of the exhaust air volume of the engine.

2) The position of the air inlet should be designed in or near the position relative to the wind direction of the generator exhaust fan.

3) The structure of the air inlet should be able to block the outflow of sound waves and be conducive to the air inlet.

In the design, the section structure of the air inlet is in the form of louver. At the same time, a wind-bucket type barrier is added on the inner wall of the air inlet to improve the sound insulation effect of the sound insulation cover.

l Noise reduction of exhaust duct

The exhaust noise of the cooling fan is also the main noise source during the operation of the unit. In order to reduce the noise of the unit, the noise reduction duct should be considered in the design. The structure form of the air duct can be referred to the following points: 1) the section shape of the air duct is broken line, which can form the reflection and noise reduction effect on the noise and sound wave; 2) there should be sound absorption material in the air duct, through the sound absorption material, absorb part of the noise energy; 3) It is best to make detachable between the air duct and the working cabin of the unit to facilitate installation, adjustment and maintenance.

l Unit layout, l

In the low noise unit, because the heat in the operation of the unit is not easy to discharge so that the working cabin temperature is high, in the design, the control panel should be separated from the working cabin, to avoid the premature aging of electrical components due to the influence of high temperature.

For the unit with low working temperature of the muffler, the muffler can be installed in the sound insulation cover, and only the exhaust tail pipe of the muffler is led out of the cover to improve the noise reduction effect. In addition, when determining the rated power of the unit, the power loss caused by noise reduction should be considered.

Design scheme and measure of noise reduction in generator room

Noise reduction system

The noise of the generator room is mainly processed in the following aspects: silencer door silencer, air inlet silencer, exhaust duct silencer, secondary silencer of smoke exhaust pipe; In order to prevent the heat generated by the smoke exhaust pipe and indoor muffler in the machine room, the smoke exhaust pipe and indoor muffler are bandage with sound insulation and fireproof rock wool material to reduce the heat of the unit to the machine room.

Manufacture scheme of noise reduction components

1) muffler door

The structure adopts the metal frame, the interior is equipped with the high strength sound insulation rock wool material, the exterior is closed with the metal plate, the metal door frame around the noise muffler door is sealed with the soft sealing hose.

2) Sound reduction of air inlet system

The diesel engine unit needs enough fresh air to burn at work, so the area design of the air inlet pipe should be paid attention to in the design of noise prevention, so as to meet the working needs of the diesel engine when the load is full. The air inlet silencing air groove designed by Yichang Company is made of galvanized iron sheet and high strength silencing rock wool.

3) Sound reduction of exhaust system

Made of galvanized iron sheet and sound-absorbing rock wool. The fan of diesel engine forces the water tank to cool, the hot air is discharged from the machine room through the exhaust groove, and the noise is transmitted outward from the guide groove of the muffler air groove. The exhaust muffler designed by Yichang Company can effectively reduce the noise passing through the exhaust duct.

4) Diesel exhaust gas system noise reduction

In order to prevent the heat generated by the smoke exhaust pipe and indoor muffler in the machine room, the smoke exhaust pipe and indoor muffler are bandage with sound insulation and fireproof rock wool material to reduce the heat emitted to the machine room; After the exhaust gas is silenced by the indoor first level silencer, there is still a higher noise from the end of the smoke exhaust pipe. A second level silencer must be installed after the first level silencer, which can effectively reduce the noise.

4 National standard for noise control (GB 12349)

Scope of application of the standard

This standard applies to the boundaries of factories and enterprises and institutions that are likely to cause noise pollution.

Standard values

All kinds of factory boundary noise standard values are listed in the following table:

Equivalent sound level Leq[dB(A)]