4843 engines

describe the operating principles of petrol engines

A model of a four stroke petrol engine.

• Rocker (A)
• Inlet Valve (B)
• Piston (C)
• Connecting Rod (D)
• Crankshaft (E)
• Camshaft (F)
• Pushrod (G)
• Exhaust Valve (H)

The 4 stroke is so called as all the required functions to make the engine run are completed in 4 strokes of the piston-- inlet, compression, power, exhaust.

The first stroke is the inlet or induction stroke. As the piston moves down inside the cylinder, the inlet valve opens allowing a fresh change of mixed gasoline and air to enter the cylinder.

After the piston has completed the inlet stroke, the inlet valve closes and the piston returns back up inside the cylinder to compress the mixture in readiness for the power phase.

After the gases have been ignited, the piston is driven down inside the cylinder forcing the crankshaft to rotate.

As the piston completes its power stroke, the exhaust valve opens in readiness for the exhaust phase.