Engine Principles

Introduction

• The engine is the device that converts the chemical energy contained in the mechanical energy.
• The energy in the fuel is converted into heat energy by burning the fuel in the process known as combustion.
• Referred to as internal combustion engines.

FOUR STROKE PETROL ENGINE

First stroke:Induction(Intake Stroke)

• The inlet valve is open and the exhaust valve is closed.When the piston drawn in that will create vacuum,cause the piston move from top dead centre to bottom dead centre.Atmospheric air pressure to force a mixture of air and fuel that is supplied by a carburettor or fuel injection system into the cylinder.

Second stroke:Compression

• Both valves are now closed and the piston is travel from bottom dead centre into top dead centre.
• The mixture of air and fuel in the cylinder in now compressed to a high pressure.
• A high pressure is required to extract the maximum amount of energy from the fuel.

Third stroke:Power

• Both valves are closed and the spark ignites the fuel.
• This causes the pressure in the cylinder to rise and the action pushes the piston down the cylinder to rotate the crankshaft.

Fourth stroke:Exhaust

• The exhaust valve is open and the inlet valve is closed.
• The piston travel from bottom dead centre to top dead centre and push out the exhaust.

The four strokes are completed in two revolutions of the crankshaft,whichis equivalent to an angular movement of 720 .