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Fundamental of Mechanical Engineering

By Ashik
International Combustion Engine
The internal combustion engine is an engine in which the combustion of a fuel (normally a fossil fuel)
occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine the
expansion of the high-temperature and -pressure gases produced bycombustion applies direct force
to some component of the engine, such as pistons, turbine blades, or a nozzle. This force moves the
component over a distance, generating useful mechanical energy.



Almost all cars currently use what is called a four-stroke combustion cycleto convert gasoline into
motion. The four-stroke approach is also known as the Otto cycle, in honor of Nikolaus Otto,who
invented it in 1867. They are;
1. Intake stroke
2. Compression stroke
3. Combustion stroke
4. Exhaust stroke
Working principle of 4-stroke cycle engines (Petrol engine):
Here's what happens as the engine goes through its cycle:
1. The piston starts at the top, the intake valve opens, and the piston moves down to let the
engine take in a cylinder-full ofair and gasoline. This is the intake stroke. Only the tiniest drop
of gasoline needs to be mixed into the air for this to work. (Part Aof the figure)

2. Then the piston moves back up to compress this fuel/air mixture. Compression makes the
explosion more powerful. (Part Bof the figure)

 3. When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the
gasoline. The gasoline charge in the cylinder explodes, driving the piston down. (Part Cof the
figure)
4. Once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaustleaves
the cylinder to go out the tailpipe. (Part Dof the figure)



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