How to Process and Analyze Noise of Diesel Generator Set

1.Noise source analysis of diesel generator set

Diesel generator noise is a complex sound source composed of multiple sound sources. According to the mode of noise radiation, it can be divided into aerodynamic noise, surface radiation noise, and electromagnetic noise. According to the causes, the surface radiation noise of diesel engines can be further divided into combustion noise and mechanical noise. Among them, aerodynamic noise is the main source of noise.

A. Aerodynamic noise is generated by the unstable process of gas, which is caused by the disturbance of gas and the interaction between gas and objects. The aerodynamic noise directly radiating into the atmosphere includes intake noise, exhaust noise, and cooling fan noise.

B. It is difficult to strictly distinguish between combustion noise and mechanical noise. Usually, the pressure fluctuations caused by combustion in the cylinder are referred to as combustion noise, which radiates outward through the cylinder head, piston, connecting rod, crankshaft, and engine body. The noise generated by the impact of the piston on the cylinder liner and the mechanical impact vibration of the moving parts is called mechanical noise. Generally, the combustion noise of direct injection diesel engines is higher than mechanical noise, while the mechanical noise of non direct injection diesel engine generator is higher than combustion noise. However, the combustion noise during low-speed operation is higher than the mechanical noise.

C. Electromagnetic noise is generated by the high-speed rotation of the generator rotor in the electromagnetic field.

2.Noise control measures

The noise of diesel generator set is mainly exhaust noise, and the noise shows obvious low frequency. If the noise source cannot be reduced, the diesel generator set can be comprehensively treated with sound insulation, sound absorption and noise elimination as required.

A. Ventilation and noise reduction in the computer room.

In practical work, when considering solutions, we need to effectively reduce noise while also meeting the air flow required for the operation of the generator set.

(1) Machine room inlet air silencing system

① In order to meet the cooling air and combustion air volume required for unit operation, the machine room adopts mechanical air intake ventilation.

② Two air inlet ducts are built with bricks outside the computer room, and a low noise axial flow fan is installed under the wall of the air inlet duct to supply air to the inside of the computer room.

③ Install a large air volume combined disc muffler in the intake duct to absorb airflow noise and mechanical noise.

④ An air inlet is installed on the outer wall of the air inlet, and a special aluminum alloy louver and protective wire mesh are installed at the air inlet to prevent foreign objects from entering the air duct.

(2) Machine room exhaust and noise reduction system

① Build two exhaust ducts with bricks outside the computer room.

② Install a large air volume combined disc muffler in each exhaust duct to absorb exhaust flow noise and mechanical noise.

③ The exhaust outlet is set directly in front of the unit, and the front end of the unit radiator is equipped with a vibration damping flexible joint and a guide air expansion and noise reduction air duct, which is connected to the exhaust hot air sound-absorbing channel.

④ Install special aluminum alloy louvers and protective wire mesh at the outlet of the exhaust duct to prevent foreign objects from entering the duct.

(3) Genset exhaust silencer

The noise reduction volume of the exhaust muffler equipped with generator set is very small. Taking the diesel generator set produced by Guangxi Dingbo Power Equipment Manufacturing Co., Ltd. as an example, it is generally 15-20dB (A), which cannot meet the requirements of environmental protection. Install a high-efficiency micro perforated plate exhaust muffler designed for high, medium, and low frequency noise on the exhaust pipe of the diesel generator. Its characteristics include high noise reduction, low resistance, and high temperature resistance of the material and structure. The exhaust pipe is connected to the flue gas outlet of the unit using metal corrugated pipes to reduce vibration and noise caused by rigid connections.

B. Sound absorption in the computer room.

The generator room has a strong sound reflection due to its brick and concrete structure. In order to achieve sound absorption effect, efficient sound-absorbing materials are reasonably installed on the walls and top surfaces of the computer room. The sound-absorbing layer structure is aluminum alloy perforated buckle plate+centrifugal sound-absorbing cotton+light steel keel+support and hanger. Original average sound absorption coefficient in the computer room α 1≈0.10, average sound absorption coefficient in the computer room after adding sound absorbing materials α 2≈0.75~0.85, the sound absorption can reach 9~12dB (A), and the reverberation time can be reduced to 2~3s. The loudness inside the computer room also greatly decreases, greatly improving working conditions and improving the sound insulation performance of the computer room.

C. Sound insulation system.

In order to ensure good sound insulation performance of the computer room, fire and sound insulation doors are installed at the connection between the computer room and the outside of the computer room, and the sealing material for the door joints is rubber sealing strips. Block other holes that may cause leakage with brick walls.

(4).Governance effectiveness

By controlling the noise outside the computer room boundary to meet the Class II standard in the national (Urban Environmental Noise Standard) (GB-3096-82), the goal of eliminating noise pollution was achieved through on-site testing of ≤ 55dB (A) during the day and ≤ 45dB (A) at night.