Analysis of Noise Source of Diesel Generator Set

Analysis of Noise Source of Diesel Generator Set
Diesel noise is a complex sound source composed of a plurality of sound sources, and the dieselve noise can be divided into aerodynamic noise and surface radiation noise according to the noise radiation. According to the mechanism, the surface radiation noise of diesel engine can be divided into combustion noise and mechanical noise. Among them, aerodynamic noise is the main noise source.
Air power noise:
The aerodynamic noise is due to the non-stable process of the gas, i.e., the gas disturbance and the interaction of the gas and the object. Air power noise directly to atmospheric radiation includes: intake noise, exhaust noise, cooling fan noise.
Intanceless noise:
The intake noise is one of the main aerodynamic noise of the diesel engine, which is formed by the periodic opening and closing of the intake valve and the pressure fluctuation change produced. When the intake valve is turned on, a pressure pulse is generated in the intake pipe, and as the piston continues to move, it is damped; when the intake doors are closed, a pressure pulse having a duration is also generated. Then periodic intake noise is generated. Its noise frequency component is mainly concentrated in a low frequency range below 200 Hz. At the same time, when the airflow flows through the intake gate flow cross section, a turbulent degrees is generated, resulting in high frequency noise generation, and since the intake valve flow cross section is constantly changing, the turbulent noise has a certain frequency range. Mainly concentrated in the high frequency range of 1000 Hz or more. When the inherent frequency of the intake air column is consistent with the main frequency of the periodic intake noise, the resonance noise of the air column will be more prominent in the intake noise.
For engines with turbocharger, due to the rotational speed of the turbocharger, its intake noise is superior to the engine of non-turbocharged booster. The noise of the turbocharger is formed by periodically cutting the rotating noise generated by the blade and the turbulent noise formed by the high-speed airflow, which is a continuous high frequency noise, mainly distributed at a frequency range of 500 to 10,000 Hz.
The intake noise is related to the engine's intake method, intake structure, cylinder diameter, and cam model. For the same engine, the rotational speed has a large influence, and the speed of the speed can be doubled to increase the intake noise to increase 10 ~ 15 dB (a).
Exhaust noise:
The exhaust noise is the main source of sound in engine noise, and its noise is generally 10 to 15 dB (a) than the engine machine noise. The engine exhaust is high temperature (490 ° C), high pressure (3 ~ 4 atmospheric pressure) gases. The exhaust process is generally divided into two stages, namely the free exhaust stage and the forced exhaust stage. The engine exhaust gas rolled out from the exhaust valve, along the exhaust tobacco pipe into the muffler, discharged from the tail tube into the atmosphere, producing the exhaust noise of the wide frequency band during this process.
Exhaust noise includes complex noise ingredients: exhaust noise in the unit time, the exhaust noise, the gas column resonance noise in the pipeline, airflow gas flow in the exhaust manifold, exhaust gas injection and impact noise, The cylinder Helmhow resonance noise, the turbulent noise inside the card door vortex noise and the exhaust system.
The main factors affecting the exhaust noise of the engine are: cylinder pressure, exhaust valve diameter, engine displacement, and exhaust valve opening characteristics. For the same engine, engine speed and load is the main factor affecting its exhaust noise.
Cooling fan noise:
Fan noise is composed of rotating noise and turbulent noise. The rotary noise is due to the periodic cutting of the blade of the fan, causing the pressure pulsation of the air to pass through the frequency of the blade, and is accompanied by a high harmonic. The turbulent noise is a turbulent degreasis due to the surrounding air caused by the fan motion, so that the air is disturbed, and the compression of the gas is formed and the sparse process is formed, which is a broadband noise.
The cooling fan noise is highly affected by the speed, and the speed can be doubled to cause its sound level to increase 10 to 15 dB (a). The fan noise is much lower than the engine noise during low speed, and it will often become the main noise source at high speed. At present, the diesel generator speed is more than 1500 rpm, which belongs to a high turnover machine.
Surface radiation noise:
Combustion noise and mechanical noise is difficult to distinguish, and the pressure vibration formed by the inner combustion of the cylinder through the cylinder head, the noise of the piston-connect rod-crankshaft - the body radiation is refurbished as combustion noise. The noise generated by the mechanical impact vibration of the piston on the hit of the cylinder line, the timing gear, the gas supply mechanism, the fuel injection system, etc., is called mechanical noise. Generally, the combustion noise of direct injection diesel engines is higher than mechanical noise, rather than the mechanical noise of the straight spray diesel engine, the sound is higher than the combustion noise, but the combustion noise is higher than the mechanical noise during low speed operation.