The exhaust system of an automobile consist of an exhaust monifold, catalytic converter, resonator and a muffler connected with a tail pipe.
Hot exhaust gas along with sound waves generated at the end exhaust stroke is sent to the exhaust manifold through exhaust valve.
Sound waves and exhaust gas pass from Exhaust manifold to catalytic converter through a pipe. Hot exhaust gases entering inside catalytic converter.
Due to partial combustion, the gases entering inside the catalytic converter consist of a mixture of a corbon monoxide (CO), unburned hydrocarbons (HC) and oxides of nitrogen (NOx) which are harmful to the environment.
Inside the catalytic conventer there consist two ceramic blocks with micro ducts consisting of platinum and rhodium in one block while platinum and palladium in the other block, acting as catalysts. The toxic gas enter into the first ceramic block and heat up simultaneously. This causes the catalyst to react with the toxic gases. As the gas enters inside, the nitrogen molecules are the first react. The catalyst causes the oxides of nitrogen to reform into nitrogen and oxygen respectively
Oxcides of Nitrogen (NOx) => Oxygen (O2) + Nitrogen (N2)
The gas then flows through the micro ducts of the second ceramic block where it reacts with the platinum and palladium.Inside the micro ducts of the second ceramic block here the carbon monoxide reacts with oxygen molecules to form carbon dioxide (CO2)
Carbon Monoxide (CO)+ Oxygen(O)=> Corbon Dioxide (CO2)
The unburned hydrocarbons also react with oxygen to form water and carbon dioxide
Hydrocarbons(HC) + Oxygen(O2) => water (H2O)+Carbon dioxide(CO2)
The exhaust gas now becomes less toxic and comes out from catalytic conventer having mixture of carbon dioxide (CO2),Nitrogen (N2) and water vapors (H2O).
The exhaust gas now becomes less toxic but consist of sound waves generated by the engine. To cancel the noise of these sound waves,in the gas is made to flow through the muffler. Muffler consist of chambers of different sizes.
The gas with sound waves enters inside the muffler into the first expansion chamber, which consist of drilled holes around its surface some of the waves come out through these holes and move back and forth against the walls of the muffler. As more waves come out through the holes, the space for movement reduces which causes friction and ultimately destroys the sound waves. Sound waves with more intensity pass through the first chamber and try to enter into the second chamber. İnto the second chamber sound waves again collide with the walls and destroy due to friction. The loudest sound wave makes through both these chambers and enters into the Helmholtz Resonator. Here the sound wave hits the wall of the resonator and bounce back, generating opposite sound wave of same frequency. This phenomenon causes the sound waves to cancel each other. Before flowing out through the tail pipe, the gas along with any sound wave is made to flow through the third chamber. Before flowing out through the til pipe, the gas along with any sound wave is made to flow through the third chamber. In the third chamber the noise further reduced due to friction .
Finally, the exhaust gases consisting of less harmful gases along with considerably low sound waves move out of the tail pipe into the atmosphere.