Before understanding the exhaust manifold, one must always have some understanding of its working environment. As the name implies, the exhaust header manifold is the first door through which exhaust gas is discharged from the engine exhaust system. It mainly gathers the exhaust gas emitted by the engine to the exhaust pipe, then passes through the three-way catalysis (gasoline engine), and is discharged into the atmosphere through the exhaust pipe. Recognizing this, it is not difficult for us to think of the design criteria of the exhaust manifold: to ensure that the engine can exhaust smoothly and to ensure that the manifold can withstand the high temperature and mechanical vibration of the engine when it is working.
Exhaust is the main factor considered in the design of the manifold shape. Car enthusiasts know that emission regulations are becoming more and more stringent now. In order to make the exhaust emissions comply with the regulations, the fuel should be fully burned as much as possible. The optimization of the exhaust system of traditional engines is also an important point. Combustion requires sufficient oxygen, so the requirement for the exhaust system is to let the exhaust gas in the cylinder be discharged normally according to the requirements, let fresh air in, and not let the excess exhaust gas stay in the cylinder to take up space.
The intake and exhaust pipes of traditional engines are all manufactured by casting. But now use stainless steel or aluminum alloy materials, these two materials can not only reduce the airflow resistance in the pipe but also reduce the weight, because stainless steel and aluminum alloy are much smaller than cast iron, so now many modification shops are modifying cars The intake and exhaust pipes are made of stainless steel or aluminum alloy.
Most of the traditional intake and exhaust pipes are in the shape of a square. This is because the square cross-sectional surface area is large, which is very beneficial to the evaporation of the oil film in the intake pipe. At the same time, the casting process is simpler than the round shape. Because the resistance of the circular section to the airflow is small, in order to obtain a higher airflow velocity, the intake and exhaust pipes of some engines adopt a circular section.
And from the perspective of installation, most of the intake and exhaust pipes of traditional engines are installed on the same side of the cylinder, but due to the structural needs of high-speed engines, the intake and exhaust pipes are mostly installed on both sides of the cylinder respectively, and the intake pipes are installed on both sides of the cylinder. Heating is by cooling water or an electric heating device. It should be pointed out here that due to the influence of the temperature of the exhaust gas, the hot and cold temperatures of the exhaust pipe change extremely quickly, and the huge heat may cause cracks in the exhaust pipe. Therefore, in order to ensure a certain thermal expansion and contraction, the exhaust installation form of the manifold is different from the intake pipe. Generally, the exhaust pipe of the engine is one cylinder and one manifold, which can reduce the heat load of the exhaust pipe.
From the shape point of view, the intake pipe can be divided into vertical inlet and convoluted inlet. Due to the small air intake resistance, the vertical air inlet is conducive to the formation of resonance at high rpm, improving the intake efficiency, and it is also convenient to arrange fuel injectors. It is generally suitable for engines that emphasize high-speed performance; Swirl flow is generated when the gas is used to increase the mixing degree of air and gasoline, which is conducive to improving the combustion efficiency in the cylinder at low speed and is generally suitable for engines that emphasize low-speed performance.
According to the principle of aerodynamics, the fluidity of the intake and exhaust pipes should be based on the flow conditions at the smallest cross-section, and in the entire intake and exhaust passage system of the engine, the smallest cross-section is at the valve gap, which is The reason why modern engines use multi-valve or increase the diameter of the valve port as much as possible.
At the same time, the influence of factors such as the size, shape, material, bending radius, and installation position of the intake and exhaust pipes on the airflow velocity must be considered, because only when various factors are well coordinated can the modified engine perform at its best.
Why are exhaust pipes curved?
First of all, it is for better heat dissipation. When the engine is running continuously, a huge amount of heat will be generated, and at this time, the temperature of the exhaust gas discharged from the cylinder is very high, up to more than 800 degrees. If it cannot be discharged in time, once the heat accumulates higher and higher, it will cause great damage to the engine.
Therefore, the technical engineer designed the exhaust pipe to be curved, so that the exhaust gas can have more time to slowly reduce the temperature when it is discharged. Otherwise, the car may emit white smoke after running for a few kilometers, or more seriously, it may directly cause cylinder failure.
In addition to heat dissipation, the exhaust pipe also has a function of noise reduction. When gasoline burns violently in the cylinder, it will make a huge noise, and this is the role of the muffler at this time.
Of course, if it is designed as a straight pipe, then not only the sound of gasoline burning, but also a large amount of exhaust gas will directly rush out of the tailpipe in the car when it is discharged, and the channel without buffer will also make noise. The curved exhaust pipe just integrates these problems. The tailpipe is equipped with a muffler and has good shock absorption performance. There is also a channel for the exhaust gas to be relaxed, and the sound is naturally relatively small.
In fact, in addition to the above two reasons, there is a more humane design that is the high temperature generated when the vehicle is driving. After passing through the exhaust pipe, try to avoid the seat to avoid burns and at the same time, it cannot be compatible with non-heat-resistant materials. It is close, so the first half will be installed in the middle of the car, but in the second half, you must pay attention to avoid the position of the fuel tank, otherwise the high temperature and the fuel tank will have unimaginable consequences, and it will easily cause scratches when passing through the bottom of the chassis. At the bumping position, a curved shape should be designed to hang in the middle without affecting the ventilation of the exhaust.
In addition, it is worth noting that a car with a large-displacement engine needs to install multiple exhaust pipes. One reason is that too much exhaust gas is generated, and multiple exhaust pipes are required to share heat at the same time, which can also achieve the effect of noise reduction. better. Another reason is that a large-displacement engine will have more cylinders, so it is easy to cause confusion and overlapping of the exhaust time of each cylinder, resulting in unsmooth exhaust, which will directly affect the performance of the engine. Therefore, the reasonable use of multiple exhaust pipes can facilitate the orderly and smooth discharge of exhaust gas.
which exhaust pipe do you prefer?
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