Engines: Motive Power Types: 4-stroke spark-ignition engines
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Topic IntroductionHelp

Basic 4-stroke principles

Summary
The five events of an internal combustion engine are Intake, Compression, Ignition, Power, and Exhaust. In a 4-stroke gasoline engine, the crankshaft does two revolutions in each engine cycle. Only one of its 4-strokes delivers energy to the crankshaft.

This is a cylinder for a 4-stroke Petrol/Gasoline engine. The first step is to get the air-fuel mixture into the chamber. Mixture enters through an inlet port that is opened and closed by an inlet valve. This is called Intake.

Next is compression. The piston compresses the air-fuel mixture into a smaller volume.

A spark across the electrodes of a spark plug ignites it, and it burns. This burning is called combustion.

The burning gases expand rapidly, and push the piston down the cylinder until it reaches bottom dead center.

The reciprocating action of the piston turns into the rotary motion of the crankshaft.

The crankshaft forces the piston back up the cylinder, pushing leftover gases out past an exhaust valve. And everything is back where it started, ready to repeat the whole process.

The whole process is a cycle. A new mixture enters and is ignited. Combustion occurs, expanding gases drive the piston down and turn the crankshaft which pushes the piston back up the cylinder.

These 5 events occur in all internal combustion engines. How they happen can change but they are always there.

In one 4-stroke cycle, the crankshaft does 2 revolutions. In those 2 revolutions how many strokes does the piston make? It does 4 strokes.

Out of those 4 strokes how many actually produce energy? In one 4-stroke cycle, only 1 stroke out of 4 delivers new energy to turn the crankshaft.