Fear not, you
have not strayed on an NSFW site!
This is a
very easy way for those who are mechanically-challenged to understand how a
4-stroke engine works. In fact, all modern light to medium engines used in
motor vehicles today are 4-stroke internal combustion (IC) engines. The four
stroke engine was first demonstrated by Nikolaus Otto in 1876, hence it
is also known as the Otto cycle. A mechanical engineer
will describe the 4 strokes of the engine as the intake stroke, the compression
stroke, the combustion stroke, and an exhaust stroke.
However, the
diesel & petrol engines differ in the manner fuel is ignited in the power
stroke.
1. The Intake
Stroke:
During this time, the piston is moving downward and only air is drawn into the cylinder. This occurs on a normally aspirated engine as a result of the difference between atmospheric pressure and the depression created by the piston and the piston ring seal. The intake valve opens up and air is sucked into the cylinder.
During this time, the piston is moving downward and only air is drawn into the cylinder. This occurs on a normally aspirated engine as a result of the difference between atmospheric pressure and the depression created by the piston and the piston ring seal. The intake valve opens up and air is sucked into the cylinder.
2. The
Compression Stroke:
The piston is moving upward in the bore and compresses the air into the very small volume of the combustion chamber and raises its temperature high enough to ensure auto-ignition of the fuel charge. The air is squeezed during the compression stroke by the movement of the piston. This intense squeezing raises the temperature of the air above 800 degrees.
The piston is moving upward in the bore and compresses the air into the very small volume of the combustion chamber and raises its temperature high enough to ensure auto-ignition of the fuel charge. The air is squeezed during the compression stroke by the movement of the piston. This intense squeezing raises the temperature of the air above 800 degrees.
3. The Power
Stroke:
As the piston reaches the top of the cylinder, during the combustion stroke, atomized fuel is injected. On contact with the very hot air, the ignited gases expand (or go “bang).
As the piston reaches the top of the cylinder, during the combustion stroke, atomized fuel is injected. On contact with the very hot air, the ignited gases expand (or go “bang).
In a petrol
engine, the spark plug fires, igniting the compressed
fuel. As the fuel burns it expands, driving the piston downward.
4. The Exhaust
Stroke:
Finally, the byproducts of combustion are expelled from the cylinder and combustion chamber. First, by the pressure differential between the bore and the exhaust port of the head (this is identified as blow down), and then by the movement of the piston upward. The waste gases exit the cylinder bore through the exhaust port in the cylinder head into the exhaust system.
Finally, the byproducts of combustion are expelled from the cylinder and combustion chamber. First, by the pressure differential between the bore and the exhaust port of the head (this is identified as blow down), and then by the movement of the piston upward. The waste gases exit the cylinder bore through the exhaust port in the cylinder head into the exhaust system.
In the four-stroke cycle,
the following sequence of events is then continuously repeated when the engine
is running.
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