The four-stroke combustion cycle

The four-stroke combustion cycle
Let us come back to the discussion about the four-stroke combustion cycle. The animation below illustrates how the four-stroke combustion cycle works in an engine with only one cylinder. When the engine goes through one cycle, the following happens:

The four-stroke combustion cycle inside a car engine with only one cylinder [iii]

1.	The first stroke is the intake stroke. In this stroke, the intake valve opens as the piston moves down from the top. As a result, a cylinder-full of air and gasoline is taken into the engine. For the combustion to occur properly, the air needs to be mixed with the tiniest drop of gasoline. (Part 1 of the animation)
2.	Then the piston moves back up to compress this fuel/air mixture between the top of the piston and the top of the cylinder. Since the compression raises both the pressure and temperature of the mixture, the explosion becomes more powerful. This stroke is known as the compression stroke. (Part 2 of the animation)
3.	As the piston approaches the top of the cylinder, the spark plug emits a spark to ignite the fuel and air mixture. The resulting explosion produces a lot of exhaust gas leading to a rapid increase in the pressure inside the cylinder. Subsequently, the piston is forced to move back downwards. During this so-called power stroke, power is transmitted from the piston to the crankshaft, which will be in turns transferred to the wheels through the other parts of the car. (Part 3 of the animation)
4.	In the last stroke, the exhaust valve opens and the exhaust gas leaves the cylinder after the piston hitting the bottom of the cylinder. Thus this stroke is also known as the exhaust stroke. (Part 4 of the animation)

After completing the four strokes, the piston reaches the top of the cylinder again and the condition of the cylinder is restored to be the same as that just before the intake stroke. So now the engine is ready for the next cycle and thus the engine can repeat the cycle again a