Which of the following components in an engine mixes fuel and air and vaporizes the fuel?

Concept:

Carburetor:

• The process of formation of a combustible fuel-air mixture by mixing the proper amount of fuel with air before admission to the engine cylinder is called carburetion and the device which does this job is called a carburetor. 
• Thus carburetor supply mixture of air and fuel with maintained air petrol ratio, generally used in the petrol engine.
• As in the CI engine, only air is compressed and then fuel is injected into the cylinder by an injector. So the CI engine does not require the carburetor.

Spark plug:

• A Spark plug is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air mixture by an electric spark.
• The function of the spark plug can be hampered by the deposition of different types of contamination such as:
  Oil fouling, Lead fouling, Carbon fouling, Graphite fouling.

Exhaust Manifold:

• It is used to transmit the exhaust gases from the cylinder to teh silencer.
• This is fitted between the cylinder head and silencer. This is made of cast iron. This is the important component of the engine.
• This arrangement is used for storing the energy and releasing the energy. 
• It is used to rotate the crankshaft continuously from the initial condition due to its inertia.
• This is fitted at the end of crankshaft it stores the power during expansion stroke and releases the energy during other strokes.

Silencer:

• After the power stroke of the engine the exhaust gases get expanded and expelled through the exhaust manifold.
• During the exhaust process when the gases are passed through exhaust manifold, due to pressure differential huge noise is produced.
• This leads to noise pollution. In order to reduce the noise pollution and to operate the engine in smooth condition silencer is used.
• Silencer acts as resistant for noise and converts the sound energy into heat.