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How does the exhaust system work?

Update:11 Mar 2021
Summary:

The function of the exhaust system is to discharge the […]

The function of the exhaust system is to discharge the exhaust gas in the cylinder into the atmosphere with the smallest possible exhaust resistance and noise. The exhaust system mainly includes exhaust manifolds, exhaust pipes and mufflers. Exhaust gas from the exhaust port connected to the combustion chamber, through the exhaust manifold, the front middle section of the exhaust pipe (including the three-way catalytic converter) and the tail section of the exhaust pipe (commonly known as the tail exhaust), and finally discharged into the outside air.

As mentioned in the modification of the intake system above, it is possible to reduce the intake resistance and exhaust resistance, increase the pressure in the cylinder, reduce the temperature at the end of the intake, reduce the pressure of the residual exhaust gas in the exhaust pipe, and increase the intake valve area. Improve the volumetric efficiency of the engine, increase the power and torque of the engine correspondingly, and improve the power performance. Therefore, in the modification of the exhaust system, the free exhaust should be expanded as much as possible to cut off the pressure difference between the cylinder and the exhaust pipe, make full use of the exhaust inertia, reduce the exhaust resistance, reduce the pressure of the residual exhaust gas in the exhaust pipe, and reduce the residual exhaust gas. The content of, finally makes the exhaust smooth and fast, improves the volumetric efficiency, and obtains better power performance. In order for the exhaust system to obtain higher exhaust efficiency, it is necessary to make full use of the back pressure (back pressure) and "sucking" effect generated by the exhaust system during operation. When the engine is working, the exhaust gas delivered by the exhaust system is not continuous, but one wave after another; the more the number of cylinders or the higher the speed of the car engine, the denser the exhaust wave. The low pressure generated after the high-pressure exhaust wave is discharged from the cylinder at a high speed is the back pressure. A proper amount of back pressure can produce a good suction effect in the exhaust system.

The principle is: if the diameter of the exhaust pipe is moderate, the first wave of exhaust gas discharged from the cylinder after expansion will force the inner wall of the exhaust pipe to be quickly discharged downstream, and at the same time, a low pressure area is generated in the upstream part to absorb the second exhaust from the engine. Wave exhaust gas. When the second wave of exhaust gas is pushed out from the inner wall of the exhaust pipe, the low pressure generated behind it is sucking the third wave of exhaust gas, and so on, so that the engine can finish the exhaust action effortlessly, and the exhaust efficiency It is also higher than not using the exhaust system at all, with less exhaust gas remaining in the cylinder, and more fresh air for combustion can be contained in the cylinder. Therefore, the exhaust system can achieve higher performance only by making full use of the back pressure and suction effect.