The purpose of an engine is to convert a fuel mixture into motion. In a piston engine-- the kind you find in American cars and most foreign cars-- four successive actions have to take place: intake, compression, ignition and exhaust. All of this takes place in the cylinder through the actions of a piston, valves and spark plug. Intake is simply the movement of the fuel mixture into the cylinder through the intake valve. Compression occurs when the piston, acting like the plunger of a syringe, moves upward in the cylinder. This compressed fuel mixture is then ignited by the spark plug. The exploding force of the mixture pushes the piston back down the cylinder, and through the use of connecting rods and the crankshaft, forces the neighboring piston up its cylinder. The exhaustion of burned gases completes the four steps. The movement of the pistons rotates the crankshaft much like pedalling a bicycle rotates the sprocket. This constant action produces smooth, even rotation which is delivered on down the drivetrain to the wheels. And that is how a piston engine works.
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