What is the four-stroke combustion cycle?

We all get into our car, turn the key in the ignition, step on the gas and off we go. But have you ever wondered how a car engine works? The principle behind how the engine works is that if you put a little bit of high-energy fuel, such as gasoline, into a small, enclosed space and add a spark, a huge amount of energy will be released in the form of expanding gas. When a cycle of hundreds of these reactions happens every minute, this energy can be used to run a car. Currently, most cars on the market use the four-stroke combustion cycle (invented by Nikolaus Otto in 1867, so sometimes it's referred to as the Otto cycle). The four strokes in the Otto cycle are the intake stroke, the compression stoke, the combustion stroke and the exhaust stroke.

As the crankshaft revolves, it moves the piston down, and the intake valve opens to let in a mixture of air and fuel (this is the intake stroke). When the piston moves back up, it compresses the air/fuel mixture (compression stroke), so when the spark plug releases a spark, the resulting explosion of fuel pushes the piston back down (combustion stroke). When the piston gets to the bottom of the stroke, the exhaust valve then opens, and when the piston moves up, it pushes the exhaust from the cylinder out through the car's tailpipe (the final stroke in the cycle – the exhaust stroke).

The engine is now ready for the next cycle to begin, so the intake valve opens and another batch of air with a tiny bit of gas is drawn into the cylinder.

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