How the Exhaust System Works

Every car possesses an exhaust system which is influential in its operation and performance. Knowledge of how the exhaust system works is bound to come in handy in identifying faulty components.

The exhaust system has a total of five components each playing their designated roles in ensuring the exhaust system works flawlessly and effectively. The five components include:

  • Exhaust Manifold
  • Catalytic Converter
  • Helmholtz Resonator
  • Muffler
  • Tail Pipe

The present exhaust system used by cars isn’t just about eliminating gaseous waste products generated within an automobile but also ensuring these gases are not harmful to the environment. Hot exhaust gas along with sound waves produced on completion of an exhaust stroke is sent through the exhaust valve to the exhaust manifold. This part of the exhaust system acts like a funnel channeling generated fumes and sound waves into the catalytic converter.

Due to the occurrence of partial combustion within the engine of a car, the gases entering the catalytic converter include:

Carbon monoxide (CO)

Unburned Hydrocarbons (CxHy)

Oxides of Nitrogen (NOx)

All of these gases are quiet toxic to the environment.

The catalytic converter consists of two blocks of catalysts; a reductive catalyst made of platinum and rhodium and an oxidative catalyst made of platinum and palladium.  The gaseous mixture through the exhaust manifold gets into the catalytic converter making contact with both catalysts. Since the bonds between the nitrogen atom and the catalyst is stronger than that between nitrogen and oxygen, the bond between oxygen and nitrogen splits with nitrogen forming a ‘temporal’ bond with the reductive catalyst. When another oxygen-nitrogen bond splits, the nitrogen here also forms a ‘temporal’ bond with the same reductive catalyst. However, nitrogen has a strong affinity for itself compared to that it has for the catalyst, so the bond between nitrogen and the catalyst splits and the nitrogen bond formed which is relatively stronger. The oxygen atoms from the oxide of nitrogen could either pair up to form molecules or exist as atoms. The nitrogen molecule leaves the catalytic converter while the catalytic surface is available for the repetition of the process for more oxides of nitrogen.

The oxidative Catalyst has an affinity for oxygen. Carbon Monoxide and Oxygen molecules get attached to the surface of the catalyst. The bond between the oxygen atoms is weaker than that between the catalyst and oxygen leading to a split in the bond between the oxygen atoms. However, carbon monoxide has a higher affinity for oxygen than the catalyst does which leads to the formation of carbon dioxide.

Also, within the oxidative catalyst unburnt hydrocarbons reacts with free oxygen molecules forming water and carbon dioxide.

CxHy + O2 –> H2O + CO2

The catalytic converter oversees the several changes like the breakdown of the oxides of nitrogen and unburnt hydrocarbon as well as the formation of carbon dioxide, water, oxygen and nitrogen molecules.

Beyond the catalytic converter, exhaust fumes consist of less toxic gases and the sound waves produced by the engine. In damping the sound wave, the exhaust fumes pass through the muffler. Within the muffler, there are many chambers of various sizes. The exhaust fumes enter the first chamber which has holes drilled all over. Some of the waves in the fumes pass through these holes and engage in an oscillatory movement against the walls of the muffler. With an increase in sound waves engaging in this process, the available space decreases rather quickly generating friction. This ultimately destroys some sound waves.

Some sound waves with a higher intensity escape the destruction within the first chamber but on entering the second chamber collide with the walls and get destroyed by friction. However some sound waves pass this chamber without getting destroyed. These waves enter the Helmholtz resonator. Within the resonator, they hit the walls and bounce back generating opposite sound wave of the same frequency leading to the sound waves cancelling themselves. The fumes are made to pass through a third chamber where friction destroys any remaining sound waves.

The exhaust fumes with less harmful gases exit the exhaust system through the tail pipe into the atmosphere.

In a nutshell, the exhaust system releases less toxic gases like CO2, H2O, N2, and O2 from the combustion of fossil fuel within the car with reduced noise.

Watch the explanation video

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