How to analyze the noise of diesel generators?
According to the working principle of the diesel generator set , the noise generation is very complicated. It is divided into the causes and parts: exhaust noise, mechanical noise, combustion noise, cooling fan and exhaust noise, intake noise, and generator noise. The following by Ito Xiaobian to everyone to analyze the noise of these six parts.
Exhaust noise
Exhaust noise is a kind of high-temperature, high-speed pulsating airflow noise. It is the largest part of the engine noise with the largest energy. It is much higher than the intake noise and mechanical noise emitted by the body and is the most important component of the total engine noise. Its fundamental frequency is the firing frequency of the engine. The main components of exhaust noise include the following: low-frequency pulsation noise caused by periodic exhaust smoke, air column resonance noise in exhaust pipes, Helmholtz resonance noise of cylinders, high-speed airflow through VALVE clearance, and tortuous pipelines. The generated noise, eddy current noise, and regenerative noise generated by the exhaust system under the excitation of the pressure wave in the pipeline, with the increase of the airflow speed, the noise frequency is significantly increased.
Mechanical noise
Mechanical noise is mainly caused by the vibration or mutual impact caused by the periodic changes of gas pressure and movement inertia force during the operation of various moving parts of the engine. Among the most serious ones are the following: the noise of PISTON crank linkage mechanism, The noise of the valve train, the noise of the transmission GEAR, the mechanical vibration and noise caused by the unbalanced inertial force. The strong mechanical vibration of the diesel generator sets can be propagated to the outside of the ground from a long distance through the foundation, and then the noise can be formed through the radiation of the ground. This structural noise propagates far and decays, and it is difficult to isolate once formed.
3. Burning noise
Combustion noise is the structural vibration and noise produced by diesel during combustion. The sound pressure level of the combustion noise in the cylinder is very high, but most of the parts in the engine structure have higher rigidity and the natural frequencies are mostly in the high-middle frequency range due to the mismatch of acoustic wave propagation frequency response due to the low frequency band. High peak cylinder pressure levels do not propagate smoothly, while cylinder pressure levels in the mid-to-high frequency range are relatively easy to transmit.
Fourth, cooling fan and exhaust noise
The unit fan noise consists of vortex noise and rotating noise. The rotation noise is caused by the periodic disturbance of the fan's blade cutting air flow. The vortex noise is generated when the airflow is separated on the rotating blade section due to the viscosity of the gas. Vortex flow, radiating a non-steady flow noise. Exhaust noise, air flow noise, fan noise, and mechanical noise all radiate through the exhaust passage.
Generator noise
V. Intake noise
When the diesel generator sets are in normal operation, they need sufficient fresh air supply to ensure the normal operation of the engine on the one hand, and on the other hand to create a good heat dissipation condition for the units, otherwise the unit cannot guarantee its performance. The air intake system of the unit basically includes the air intake channel and the air intake system of the engine itself. The air intake channel of the unit must enable the fresh air to smoothly enter the equipment room. At the same time, mechanical noise and airflow noise of the unit can also be radiated to the equipment room through the air intake channel. outside.
Sixth, generator noise
Generator noise includes electromagnetic noise caused by magnetic field pulsation between the stator and the rotor, and mechanical noise generated by the rotation of the rolling bearing.
According to the noise analysis of the diesel generator set above. Generally, the following two methods are used for the noise of the generator set:
The soundproof unit is used for noise reduction or purchase in the oil machine room (its noise is 80db---90db).
Room noise reduction needs to deal with the above causes of noise separately. The main methods are as follows:
1. Intake and exhaust noise
The air intake and exhaust passages of the equipment room are respectively made of soundproof walls, and silencers are installed in the air intake passage and exhaust passage. There is a distance buffer in the channel, which can reduce the intensity of the radiation emitted from the inside of the room.
2. Control mechanical noise
The sound-absorbing and sound-absorbing materials with high sound absorption coefficients are laid on the top and all sides of the room to eliminate indoor reverberation and reduce the acoustic energy density and reflection intensity in the equipment room. In order to prevent noise from radiating through the door, a fireproof soundproof iron door is provided.
3. Control of smoke emission
The exhaust system is eliminated at the original level, which can ensure the effective control of smoke emission from the unit. The length of the exhaust pipe is more than 10 meters to increase the pipe diameter to reduce the exhaust back pressure of the generator set. The above processing can improve the noise and back pressure of the generator set. Through the noise reduction processing, the noise of the generator set in the engine room can meet the user's requirements outdoors.
Noise reduction in the engine room generally requires sufficient space in the engine room. If the user cannot provide a room with a sufficient area, the noise reduction effect will be greatly affected. It can not only guarantee the noise control, but also make the generator set work normally. Therefore, the air intake passage, exhaust passage, and staff's operating space must be installed in the machine room.
Ito recommends that all users: Diesel generators need to be loaded with false loads after noise reduction to correct the actual power of the diesel generators (the power of the oil generator will decrease after noise reduction) and to avoid accidents and improve safety. coefficient
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