(1) Aerodynamic noise
During the operation of the diesel unit, noise is generated between the air and the diesel unit due to the disturbance of the air. This noise directly generates radiation to the outside, including: the noise of the exhaust system, the noise of the intake system, and the cooling of the diesel engine. Rotating noise of the fan.
(1) Exhaust system noise. The most direct noise source of diesel generator sets is the noise generated by the exhaust system. This noise is relatively large in intensity. Compared with normal engine noise, its noise value is about 10~15dB (A) higher. When the generator set is running During the process, the high-temperature and high-pressure exhaust gas must be continuously discharged. According to the operating state of the generator set, the exhaust system has two stages when exhausting, namely, the generator set free exhaust and the generator set forced exhaust. When the exhaust gas of the generator set is discharged from the exhaust valve, it will flow from the exhaust pipe to the muffler. Finally, it is discharged into the air through the tail exhaust pipe. During the entire exhaust process, a large amount of exhaust noise will be generated, which is also the main noise source of the diesel generator set. The noise generated during the exhaust process is analyzed, and it is found that the components of the noise source are relatively complex, including the noise generated by the frequency of the exhaust system exhausting the number of times per unit time, as well as the noise of the exhaust gas resonance in the exhaust pipe and the exhaust gas. The air flow from the nozzle is blowing noise, etc. The main reasons that can affect the noise of the exhaust system of the generator set are the internal pressure of the engine cylinder, the pipe diameter of the exhaust system, the rated displacement of the generator set, the operating speed and workload of the generator set, etc., which improve the work of the generator set. Loading or increasing engine rpm increases the flow of gas, resulting in increased exhaust noise.
(2) The noise of the intake system. The noise generated by the intake system is one of the main noises of the diesel generator set. The main reason is that the intake port is constantly switched and closed according to the intake demand of the generator set, which leads to the continuous change of the pressure of the intake system and causes the noise. When the intake system is working, a certain pressure pulse is formed in the intake pipe, which causes the intake system to generate periodic noise. The audio frequency range of this kind of noise is generally around 200Hz. At the same time, when the air flow enters the system, it will flow through the intake pipe, which will lead to the occurrence of kicking and disengagement. This situation will lead to the formation of high-frequency noise in the intake system of the engine. Usually, the airflow in the intake pipeline is constantly changing, so the frequency band of this noise is also relatively fixed, and the general concentration range is around 1000Hz. When the noise frequency of the intake cycle and the air column in the intake system are consistent, airflow resonance will occur, resulting in an increase in the noise of the intake system. For different generator sets, the noise produced by different superchargers is also different. Compared with the non-turbocharged generator set, the noise intensity of the turbocharged generator set is obviously different. This is due to the relatively high speed of the turbocharged generator set, which results in relatively strong airflow generated by the air intake system of the engine for air cutting, resulting in high-frequency noise. The frequency distribution of this noise is generally in the range of 500~ between 10000Hz.
(2) Surface radiated noise
The surface radiation noise of diesel generator sets is difficult to distinguish in a strict sense. Combustion noise is generally the pressure vibration generated by diesel combustion inside the cylinder, which acts on the mechanical components of the overall cylinder and radiates a certain amount of noise to the outside. During the operation of the generator set, the mechanical parts of the generator set will continuously collide with each other, resulting in mechanical noise. Under normal circumstances, when the generator set rotates at a low speed, the combustion noise generated is higher than the mechanical noise.