Views:1037 Author:Site Editor Publish Time: 2021-05-28 Origin:Site
The exhaust manifold is connected to the engine, and the length and shape of the manifold can affect the performance of the engine by affecting the airflow. Related to engine performance, the exhaust manifold has a greater impact, and the back pressure caused by the exhaust system. A more intuitive understanding is that if the back pressure is too large, the exhaust cannot proceed smoothly, and it will block the passage or the exhaust gas in the cylinder. It cannot be discharged smoothly. In order to remove the exhaust gas, the piston needs to consume more energy to push it out, which will increase the power consumption of the whole machine. In addition, due to poor exhaust, the exhaust gas remaining in the cylinder increases, and the exhaust gas temperature is higher Large, it will take up the space for fresh air to enter the cylinder, and the combustion will be affected.
First look at the composition of the exhaust system:
From the exhaust manifold to the exhaust tail pipe, the system includes Y-tube, catalytic converter, flexible pipe, front silencer, rear silencer, intermediate connecting pipe, tail pipe, hook, and hook vibration isolation Parts.
The picture shows the exhaust system of a V-type engine. In fact, the Y-tube is only used by the V-type engine.
One end of the exhaust system is connected to the exhaust manifold, and the other end is connected to the car body through a hook.
Generally speaking, the flexible connecting pipe is the dividing point between the hot end and the cold end, of course there are special cases. Close to the engine is the hot end, mainly exhaust manifolds and catalytic converters. The temperature can reach 800~900°. The cold end far away from the engine is mainly the muffler. Cold does not mean that the temperature is really low...
As you can see in the picture, the main arrangement behind the double outlet is the muffler.
There are single-in and single-out, single-in and double-out, double-in and single-out, double-in and double-out, and two independent exhaust systems.
Generally speaking, single inlets are mainly used on four-cylinder engines, and dual inlets are used on V-type engines.
Both single outlet and dual outlet are used in four-cylinder engines and V-engines. The last independent dual exhaust system is used in V-engines.
Single-entry dual-entry should be well understood. In-line engines only need one exhaust channel, while V-type engines are a bit like folding in-line cylinders in half, with one exhaust channel on each side.
There are many sources of exhaust noise.
For example, when air flows in a pipe, the sound caused by its own vibration caused by its own energy, when the flow rate is constant, the larger the pipe diameter, the more stable the airflow, and the lower the sound. If the exhaust pipe is designed from an acoustic point of view, this is the consideration. Part of the noise.
In addition, because the exhaust valve keeps opening and closing, it will cause periodic and unstable air flow. This part of the airflow will cause sudden changes in the cross-sectional area of the pipe, or the elbow will form an impact, causing noise.
in addition, the friction between the air and the pipe wall will also Will form noise.
There is also a kind of radiated noise. When the vibrating body is in contact with the fluid, it will push the fluid and produce sound. A microphone is an example of this. The exhaust system is excited by the vibration of the engine and the car body, which will cause the entire structure to vibrate, as well as the pulse fluctuation of the air flow, which will cause this kind of noise.
The main method to eliminate noise is the muffler. The latter types of noise cannot be avoided, and the design of the pipeline cannot be considered too much. There are also several types of mufflers, such as a resistive muffler that reflects energy back to the sound source to suppress sound, or a resistive muffler that uses sound-absorbing materials to convert sound energy into heat. The noise in the engine has a narrow band of pure tones, which is more suitable for resistive silencing, and the mixed sound is broadband, which is more suitable for resistive silencing.
At the very end of the exhaust, there is a tailpipe.Generally speaking, when a stone is thrown into the water, ripples are formed. When the ripples reach the river bank, because the earth serves as a boundary, the ripples can only reflect themselves back. A simple and imprecise understanding is that the momentum and kinetic energy of high school have different qualities. The effect of small balls colliding.
In the part of the tail pipe, the airflow has to flow out into the atmosphere, and the atmospheric environment is quite stable in the pipeline, so the pulsation of the airflow here is a bit similar to water waves.
There are two main types of noise generated in the tail pipe.
One is the aforementioned dynamic noise caused by the stable air flow, and the other is the friction noise caused by the unstable air flow. When the low-speed air flow is slow, the former is dominant, and when the high-speed air flow is fast, the latter is dominant.
It can be seen in the figure that the total tailpipe noise is the dominant aerodynamic noise trend at low speeds, but has no influence at high speeds, and is dominated by friction noise.
In addition, when the air flow rate is constant, the larger the pipe diameter and the larger the cross-sectional area, the slower the air flow velocity, and the friction noise can be better suppressed.
OK, the basics have been said.
The difference between single outlet and double outlet is actually the rear muffler, there is one or two differences.
For example, the volume of the front muffler is the same, and the volume of each rear muffler is the same. The double outlet has one more exhaust channel and one rear muffler than the single outlet. The airflow can circulate from two branches. The friction noise of the tail pipe , Will be greatly reduced.
Generally speaking, a four-cylinder engine uses a single exhaust system and a dual exhaust system. There is little difference between low speeds. After medium and high speeds, friction noise dominates. The tailpipe noise of the dual exhaust system will be lower than that of the single exhaust system. 2 to 7 decibels, it can be seen that engines with higher speeds (usually better performance) are more willing to choose dual-exhaust exhaust systems, but the use of dual exhaust systems will increase costs and restrict installation space.
GRWA focuses on automotive exhaust systems. It develops and produces a variety of automotive exhaust systems and mufflers, elbows, tail throats and other system-related accessories. Whether you have single-exhaust, double-exhaust or other problems related to automotive exhaust systems, You can contact me for consultation, I will provide you with the best quality products and the most reasonable prices. In addition, we have the ability of drawing research and development, and can provide you with customized services.