What is exhaust muffler?

Exhaust Muffler refers to the airflow pipe with noise propagation at the same time, which can be attenuated or reflected back by using the pipe with sound-absorbing lining and the elbow or the pipe with sudden change of cross section area and other discontinuous acoustic impedance. The former is called exhaust muffler, the latter is called exhaust muffler,also has impedance compound type exhaust muffler. Its material is mainly carbon steel or stainless steel. 

The principle is that the automobile exhaust pipe is composed of two pipes with different lengths, and the two pipes are separated and then intersected. Because the difference of the length of the two pipes is equal to half the wavelength of the sound wave emitted by the car, the interference of the two lines of sound cancels out the sound intensity at the time of superposition. 

This article contains the following:

• Main knot

• Key role

• Common faults 

Main knot 

Automobile muffler can be divided into three types according to its principle and structure: exhaust muffler, exhaust muffler and impedance compound muffler 

1.Exhaust muffler is to reflect and interfere with the sound wave during propagation, and reduce the sound energy to achieve the purpose of silencing noise when the interior is composed of various muffler units such as expansion chamber, resonance chamber and so on through pipes and partitions. Exhaust muffler noise frequency band is limited, usually for low, medium frequency band sound effect is good, high frequency noise effect is poor, truck mostly use resistance muffler. 

2.Exhaust muffler E is a muffler which is filled with sound-absorbing material around the pipe through which the internal exhaust passes to absorb sound energy to achieve the purpose of silencing noise. It has good effect on medium and high frequency noise suppression, and is used as automobile exhaust muffler less, usually combined with resistance muffler. 

3. The impedance compound muffler is a muffler composed of resistant muffler unit and sound-absorbing material respectively. It has good silencing effect on low, medium and high frequency noise. 

Key role 

reduce the exhaust noise of the engine, and make the high temperature exhaust gas can be discharged safely and effectively. As part of the exhaust pipe, the exhaust muffler should ensure its smooth exhaust, low resistance and sufficient strength. The muffler shall be subjected to high temperature exhaust at 500°C to 700°C to ensure no damage and no loss of silencing effect within the mileage prescribed by the automobile. 

Related Application 

Automobile noise mainly comes from automobile exhaust noise. If no muffler is added, the noise can reach more than 100 decibels at a certain speed. The second is engine noise and tire noise, which can reach more than 90 decibels when the car is running normally, while tire noise can reach about 95 decibels when the speed is above 90 km/h. Therefore, the addition of mufflers in the exhaust system can reduce the vehicle exhaust noise by 20-30 dB. On the engine side, replacing diesel engine with gasoline engine can reduce engine noise by 6-8 dB.

Common faults 

Automobile muffler is a special equipment to prevent and control the noise of airflow which hinders the sound transmission. At present, in order to restrain the environmental noise caused by high pressure airflow emission, there are many kinds of mufflers in the world, most of them adopt the principle of impedance compound type silencing. However, due to the complex structure, large weight, high temperature oxidation sound absorption filler, high speed air flow impact sound absorption filler, water and gas penetration sound absorption filler and other reasons, resulting in muffler maintenance frequently, poor noise attenuation effect, short service cycle and so on, has always been the main problems faced by automotive silencers. 

Fault phenomenon: a Dongfeng EQ1090D car in the driving muffler firing phenomenon, stop check, when the ignition coil high-voltage main fire line pulled down, at the distance of the cylinder block 34mm test fire, pull the distributor power off contact or shake the crankshaft, fire jump are normal, but found that the distributor power off contact ablation phenomenon. After grinding the contact with the sand bar and adjusting the gap to 0.35-0.45mm, the engine started to work normally, but when the car drove about 40 kilometers, the muffler appeared the phenomenon of firing again. 

Fault checking and troubleshooting: according to the above phenomenon, the reasons of muffler firing are carefully analyzed, in order to find out the crux of the fault, the ignition order, the spring force of the contact arm of the sub-electric power off, the ignition timing, the spark plug and so on have not found the problem. Continue to check carburetor air filter, valve clearance also no results. Starting the engine again is normal, but not long after the old illness has returned. 

Stop and check the sub-part again. After disassembly and careful inspection, it was finally found that the copper glue wire from the broken electrical contact arm to the low voltage connection post broke at the corner, leaving only a few fine copper wires connected. After replacing the broken copper glue line, the fault phenomenon disappears.