According to the working principle of gas unit, the generation of noise is very complex. From the causes and parts, it can be divided into exhaust noise, mechanical noise, combustion noise, cooling fan and exhaust noise, air intake noise and generator noise.

一.排氣噪聲

1、 Exhaust noise

排氣噪聲是一種高溫、高速的脈動性氣流噪聲，是發(fā)動機噪聲中能量大，成分多的部分。比進氣噪聲及機體輻射的機械噪聲要高得多，是發(fā)動機總噪聲中主要的組成部分。它的基頻是發(fā)動機的發(fā)火頻率。排氣噪聲的主要成分有以下幾種：周期性的排煙引起的低頻脈動噪聲、排煙管道內的氣柱共振噪聲、汽缸的亥姆霍茲共振噪聲、高速氣流通過氣門間隙及曲折的管道時所產(chǎn)生的噪聲、渦流噪聲以及排煙系統(tǒng)在管道內壓力波激勵下所產(chǎn)生的再生噪聲等，隨氣流速度增加，噪聲頻率顯著提高。

Exhaust noise is a kind of high-temperature, high-speed pulsating airflow noise, which is a part of engine noise with high energy and many components. It is much higher than the intake noise and the mechanical noise radiated by the engine body, and it is the main part of the total engine noise. Its fundamental frequency is the firing frequency of the engine. The main components of exhaust noise are as follows: low frequency pulsating noise caused by periodic exhaust, gas column resonance noise in exhaust pipe, Helmholtz resonance noise of cylinder, noise produced when high-speed air flows through valve clearance and tortuous pipe, vortex noise and regenerative noise produced by exhaust system under pressure wave excitation in pipe, etc In addition, the noise frequency increases significantly.

二.機械噪聲

2、 Mechanical noise

機械噪聲主要是發(fā)動機各運動部件在運轉過程中受氣體壓力和運動慣性力的周期變化所引起的震動或相互沖擊而產(chǎn)生的，其中嚴重的有以下幾種：活塞曲柄連桿機構的噪聲、配氣機構的噪聲、傳動齒輪的噪聲、不平衡慣性力引起的機械震動及噪聲。柴油發(fā)電機組強烈的機械震動可通過地基遠距離傳播到室外各處，然后再通過地面的輻射形成噪聲。這種結構噪聲傳播遠、衰減少，一旦形成很難隔絕。

The mechanical noise is mainly caused by the vibration or mutual impact of the moving parts of the engine caused by the periodic changes of the gas pressure and the motion inertia force in the process of operation. The serious ones are as follows: the noise of the piston crank connecting rod mechanism, the noise of the valve distribution mechanism, the noise of the transmission gear, the mechanical vibration and noise caused by the unbalanced inertia force. The strong mechanical vibration of diesel generator set can be transmitted to all parts of the outdoor through the foundation, and then form noise through the ground radiation. This kind of structure has the advantages of long-distance noise propagation and low attenuation, so it is difficult to isolate once it is formed.

三.燃燒噪聲

3、 Combustion noise

燃燒噪聲是柴油在燃燒過程中產(chǎn)生的結構震動和噪聲。在汽缸內燃燒噪聲聲壓級是很高的，但是，發(fā)動機結構中大多數(shù)零件的鋼性較高，其自振頻率多處于中高頻區(qū)域，由于對聲波傳播頻率響應不匹配，因為在低頻段很高的汽缸壓力級峰值不能順利地傳出，而中高頻段的汽缸壓力級則相對易于傳出。

Combustion noise is the structural vibration and noise produced in the process of diesel combustion. The sound pressure level of combustion noise in the cylinder is very high. However, most parts of the engine structure have high rigidity, and their natural frequencies are mostly in the middle and high frequency region. Due to the mismatching of the response to the sound wave propagation frequency, the peak value of high cylinder pressure level in the low frequency band can not be smoothly transmitted, while the cylinder pressure level in the middle and high frequency band is relatively easy to transmit.

四、冷卻風扇和排風噪聲

4、 Cooling fan and exhaust noise

機組風扇噪聲是由渦流噪聲和旋轉噪聲組成的，旋轉噪聲由風扇的葉片切割空氣流產(chǎn)生周期性擾動而引起；渦流噪聲是氣流在旋轉的葉片截面上分離時產(chǎn)生的，由于氣體的粘性引起的旋渦流，輻射一種非穩(wěn)定的的流動噪聲。排風噪聲、氣流噪聲、風扇噪聲、機械噪聲均是通過排風的通道輻射出去的。

The fan noise of the unit is composed of vortex noise and rotating noise, which is caused by the periodic disturbance of the air flow cut by the blades of the fan; the vortex noise is caused by the separation of the air flow on the rotating blade section, which is caused by the viscosity of the gas and radiates an unstable flow noise. Exhaust noise, airflow noise, fan noise and mechanical noise are radiated out through the exhaust channel.