Motorcycles were the most popular means of transportation in the past, and until now, many people still like to use them. Compared with cars, they are much cheaper, very flexible and rarely need major maintenance

Careful friends will find that our car exhaust pipe is not straight, but beat around the Bush, with different thickness. Why do you want to do this? Isn't it easier to design straight?

 

In fact, the existence of everything is reasonable. Since engineers design like this, they must have his reason. Today, let's talk about the secrets hidden in the automobile exhaust pipe.

 

A complete exhaust pipe is divided into hot end and cold end according to professional terms, and into front section, middle section and rear section according to industry terms. A plurality of flanges are used for connection in the middle, and three-way catalyst, silencing drum and bellows are set for soft connection and hard connection.

 

The reason why it is so complicated is that each part has different division of labor, performs its own duties and cooperates with each other to ensure the normal operation of the engine. To sum up, automobile exhaust pipe mainly has the following functions:

 

First, purify the combustion waste gas. The combustion of gasoline will produce harmful gases such as CO, HC and NOx, which will pollute the environment and threaten the lives of animals and plants. In order to avoid this problem, engineers try to make the tail gas undergo chemical reaction in the emission process to oxidize and reduce the harmful gas into harmless gases such as CO2, H2O and nitrogen, that is, three-way catalytic reactor. It is called three-way catalyst because the device can reduce three harmful gases into harmless gases at the same time.

 

Its reaction condition is high temperature, so it is installed in the front section of the exhaust pipe and reacts with the help of the heat of gasoline combustion.

 

Second, reduce noise. The middle and rear sections of the exhaust pipe generally have a relatively thick protrusion, which is the silencing drum. The device has a special structure, which can make the exhaust sound waves of the engine interfere with each other and cancel each other, so as to achieve the purpose of reducing noise.

 

In addition, a section of metal hose connection is generally set in the exhaust pipe, which can effectively eliminate vibration and further reduce noise.

 

Third, ensure a certain exhaust back pressure. This is also the most direct reason why the exhaust pipe turns around. So what does exhaust back pressure mean for engine efficiency? As described in the previous article engine valve distribution system, when fuel is burned in the cylinder to do work, air supply and exhaust are required. The inlet valve and exhaust valve are opened alternately, but there is a certain superposition. In other words, when the exhaust valve is not fully closed, the inlet valve has been opened. In this state, if the exhaust pressure is too high, the exhaust gas cannot be discharged in time, and a large amount of air cannot come in, which affects the air-fuel ratio and reduces the engine power. On the contrary, if the exhaust pressure is too low, the mixed gas into the cylinder will be discharged together with the exhaust gas, resulting in fuel loss. Therefore, exhaust back pressure is very important to engine combustion efficiency.

It is generally installed in the first drum of the automobile exhaust main pipe, which is a device similar to the marching kettle.

People with a little common sense about cars know that the exhaust of cars is different in style, location and even quantity. So what are the reasons for the different positions of the exhaust pipes of these cars?