Exhaust noise generation mechanism: During the working process of the diesel engine, the flow of the gas is unstable at the exhaust valve. It is transmitted to the outlet of the exhaust system in the form of pressure fluctuation, and the velocity fluctuation occurs at the exit of the tail pipe. Radiated noise, it can be seen that the exhaust noise is derived from the unstable flow in the exhaust system. The definition of exhaust noise generally refers to the total noise radiated from the exhaust system, including the radiated noise of the pipe wall and the muffler wall and the aerodynamic radiation noise at the exit of the tail pipe. If the wall of the exhaust system and the muffler wall are Assuming that it is rigid, exhaust noise refers to only aerodynamic noise. The most effective way to reduce exhaust noise is to design an efficient, low-resistance exhaust silencer. The main factors affecting exhaust noise are engine speed, number of cylinders, load, and exhaust pipe size.
When the exhaust of the internal combustion engine starts, the gas temperature is about 800-1000 ° C, and the pressure is about 0.4-0.5 Mpa. However, when the exhaust valve opens to a gap, the exhaust gas rushes out of the gap in the form of a pulse, forming a high energy and a very high frequency. Complex noise. According to the mechanism of noise generated by the exhaust process, there are the following components.
1 Gas pressure pulsation sound.
2 Eddy currents that occur through valves, valve seats, etc.
3 Noise due to boundary layer airflow disturbance.
4 Exhaust outlet jet noise.