The exhaust system is an important part of the automobile engine. It not only affects the performance of the engine, but also affects the emission and noise control of the vehicle. Let's take a closer look at the various components of the exhaust system and how they work.
Exhaust inertia
Gas has a certain inertia during the flow process, and the exhaust inertia is greater than the intake inertia. Using the energy of exhaust inertia can improve exhaust efficiency, which is especially important in high-performance engines. Many people think that the exhaust gas is pushed out by the piston during the exhaust stroke, but in fact, as soon as the exhaust valve opens, a large amount of exhaust gas will be ejected from the exhaust valve at a very high speed. At this time, the state is not pushed out by the piston, but ejected by itself under pressure. After the exhaust gas enters the exhaust pipe, it immediately expands and decompresses, forming a negative pressure state.
Exhaust pulse
The exhaust pulse is a pressure wave that is transmitted in the exhaust pipe to form a pressure wave. The energy of the positive pressure wave and the negative pressure wave can be used to improve the intake and exhaust efficiency. The energy of the positive pressure wave and the negative pressure wave is the same, but the direction is opposite.
Pressure wave
When the exhaust gas passes through different cross-sectional spaces, a pressure difference will be generated, forming a pressure wave. The maximum pressure wave usually occurs at the end of the exhaust pipe, and the pressure wave is transmitted back and forth between the exhaust port and the exhaust valve. The more reflections there are, the less energy there is until a new pressure wave is generated. In order to utilize the pressure wave, the opening time of the exhaust valve is very important. If negative pressure is generated when the exhaust valve is opened, the exhaust efficiency can be improved. In order to change the arrival time of the negative pressure wave, the exhaust pipe length must be considered because the conduction speed of the pressure wave remains unchanged.
Suction phenomenon
The exhaust gas entering the manifold produces a suction effect on other unexhausted pipes due to flow inertia. The exhaust gas from the adjacent pipes is sucked out. This phenomenon can be used to improve the exhaust efficiency. When one cylinder is exhausted, the next cylinder begins to be exhausted. The exhaust pipes are combined based on the ignition relative cylinder as the grouping standard, and another group of exhaust pipes are combined to form a 4 in 2 in 1 type, using the suction phenomenon to help exhaust.
Muffler
If the high-temperature and high-pressure exhaust gas discharged by the engine is discharged directly into the atmosphere, the gas will expand rapidly and produce a lot of noise. Therefore, a cooling and silencing device is required. There are many silencer holes and resonance chambers inside the muffler, and the inner wall has glass fiber sound-absorbing cotton to absorb vibration and noise. The most common type is the expansion type muffler, which must have a long and short chamber inside. Because a short-barrel expansion chamber is needed to eliminate high-frequency sounds, and a long-barrel expansion chamber is used to eliminate low-frequency sounds. If only the expansion chamber of the same length is used, only a single audio frequency can be eliminated. Although the decibel is reduced, it cannot produce a sound that is acceptable to the human ear. After all, the design of the muffler must consider whether the engine exhaust sound can be accepted by consumers.
Through the reasonable design and configuration of these components, the exhaust system can not only improve the performance of the engine, but also reduce noise pollution, making the car run more smoothly and efficiently.
