How does mufflers work?

Who would not have seen those hollow pipe like structures emitting smokes out of vehicles? The silencers or the mufflers are arrangements on vehicles which absorb the unwanted sound of engines and provide them with their characteristic sound. They are connected to the exhaust manifolds of engines and provides  path for exhaust gases to be discharged suitably to the atmosphere. They also contain catalytic converters about which we will talk later on.

Silencer of a scooty 

Parts of silencers

The silencers can be mainly divided in to three  parts

1.Catalytic converters

2.Mufflers

3.Tail pipes

Working of mufflers

The mufflers has to handle exhaust gases at very high temperature. Those gases can cause corrosion of their inner walls, so they are generally made from corrosion resistant matterials like stainless steel or may also be chrome plated.  The exhaust gases emitted out of  engines have very high pressure and  high frequency sound waves. These gases move through the silencer pipes to the catalytic converters where they are reduced and oxidised simultaneously to reduce NOx to N2 and oxidise CO and hydrocarbons to CO2 and water.  Afterwards, they move to mufflers , which help in muffling or reducing the sound. The inside walls of muffler contain sound absorbing matterial like glass wool . These materials also help in absorbing of sound waves. The structure of mufflers contain perforated pipes as shown in fig. below.

The exhaust gases with high vibration enter at left end. As they move through the perforated piped, some sound waves leak through the pores on pipes and either get absorbed or get cancelled out by colliding with other waves. The gases move further and come to second compartment and get reflected by the walls. The sound waves reflected from the right wall collide with the incoming waves and cancel them out. From the second compartment gases move again to left side to the first compartment. And again through the third pipe they move on to the tail pipe. While moving through perforated pipes and left-right compartments, most of the high frequency sound waves are cancelled out due to interference with other waves or get absorbed. At last, all the exhaust gases pass through the tail pipe into the environment. While moving through the muffler, most of high frequency sound waves get cancelled out by collision with other waves and the noise of engine is reduced to a bearable level. 

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Sound of Royal Enfield

Royal Enfield motorcycles have a characteristic powerful sound. Everyone of you must have listened to it. But, have you ever wondered why it is so? Let me explain.

The loud sound of Royal Enfield bikes is not their real sound. The real sound of Royal Enfield bikes is powerful but they do have such high base for which they are famous. This sound is achieved  when these bikes are fitted with some specially designed silencers. These silencers do not have mufflers. They contain a simple pass way for exhaust gases. Their internal walls contain sound absorbing materials, which absorb the extremely loud sound waves, that otherwise have caused a lot of irritation. The most of the sound waves pass on to the atmosphere without any muffling. But in this process their bass is improved significantly.