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How exhaust system works?

First things first, Exhaust system is not a must have thing; yes you can drive your vehicle without an exhaust system. So the big question is why we have one in our cars. Exhaust system does two things, reduces the amount of harmful gas output of the engine and reduces the engine noise.


Engines generate power by burning fuel, this process is actually an explosion, when a spark is created inside the pressurized air fuel mixture, the result is a huge explosion inside the combustion chamber, this explosion creates two things, a huge sound (because of the release of highly compressed gas) and some gases that are not friendly to the environment. The purpose of the exhaust system is to reduce these as much as possible.

Let’s look at the components of an exhaust system.

  • Exhaust manifold
  • Oxygen sensor
  • Catalytic converter
  • Muffler

Let’s look at each part one by one.

Exhaust manifold

The exhaust system is connected to the engine head with the exhaust manifold. The exhaust line (from exhaust valve) of each cylinder is connected together with the use of exhaust manifold.

 

If you look under the hood of your car you might notice something similar to above  picture (sometimes your car may have an engine cover, in this case you might have to remove it to check these :D ).

Oxygen sensor

These were originally called lambda sensors, most cars have at least one oxygen sensor, and new cars have more than one most of the times. This can be located before the catalytic converter and if the vehicle has more than one sensor the others will be located after the catalytic converter.

As the name implies, the purpose of this sensor is to measure the amount of oxygen in the exhaust gas. If the exhaust gas has more Oxygen, the computer (ECU) of car will increase the amount of fuel entering the combustion chamber, if the oxygen amount is less the computer will decrease the amount of fuel released to the combustion chamber. (This process is called making the engine run lean or rich), over the years the exhaust gas stuff will gather around the sensor and this will make the sensor to function poorly, and the result will be a drop in performance and increase in the exhaust emissions.

Catalytic converter

This is the device that saved the world from pollution; the purpose of the device is to convert the harmful exhaust gases to less harmful gas. Even though the structure of the catalytic converter is simple, the cars won’t be here if this device was not invented.

So where is this Cat (catalytic converter) located.

If you look under your car you might notice something similar to this close to the engine or at the center of the car. (The oval shaped thing close to exhaust manifold)

When you burn Petrol, other gases are released, Nitrogen, Carbon Dioxide, Water vapor, Carbon Monoxide, Hydro carbons and Nitrogen Oxides.

Hydro carbons, Nitrogen Oxides, and Carbon monoxide are the stuff that needs to be filtered. Inside Cats there are ceramic structures coated with platinum, rhodium or palladium (expensive stuff J). This ceramic structure is designed in similar to honey comb structure to create a maximum surface area inside a small area.

 

There are two sections inside this these Cats, Reduction Catalyst and Oxidation Catalyst. Reduction Catalyst lower the number of Nitrogen Oxides by converting them to Nitrogen gas and Oxygen, and the Oxidation Catalyst convert the Carbon Monoxide gas in to Carbon Dioxide, which is less harmful .

Muffler

This is the part which makes the car silent (on in my case sound better ;-) ).

Because of the pressure inside the combustion chamber the exhaust gas exits from the engine (exhaust valve) extremely fast, thus making a huge sound.  You might have noticed (heard) some cars without mufflers or exhaust system, they are so loud.   Inside mufflers the are some tubes containing holes, these tubes work similar to an musical instrument, by varying the hole design and tube lengths we can make the car sound better or silent.  To explain how this works we must first look at some physics stuff.

We here sounds because of sound waves, when sound waves hit another sound wave, because of the point they hit. The wave’s amplitude gets reduces or increased, this is called constructive interference and destructive interference of waves.  This is done inside the muffler. Because of this the sound waves get cancelled out, resulting a silent car. By changing the internal layout of the mufflers the sound can be improved or tuned just like a musical instrument. :D

That’s it, Now you know how a exhaust system works, so the next time you notice a leak in the exhaust system,  get it fixed, save the environment , save fuel, save money.

 

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