simple four stroke engine working, merits and demerits over two stroke engines.

GASOLINE ENGINES

4-STROKE Petrol - Working Principle:

Intake Stroke:

•        Intake valve opens.

•        Piston moves down, ½ turn of crankshaft.

•        A vacuum is created in the cylinder.

•        Atmospheric pressure pushes the air/fuel mixture into the cylinder.

Compression Stroke:

•        Valves close.

•        Piston moves up, ½ turn of crankshaft.

•        Air/fuel mixture is compressed.

•        Fuel starts to vaporize and heat begins to build.

Power Stroke:

•        Valves remain closed.

•        Spark plug fires igniting fuel mixture.

•        Piston moves down, ½ turn of crankshaft.

•        Heat is converted to mechanical energy.

Exhaust Stroke:

•        Exhaust valve opens.

•        Piston move up, crankshaft makes ½ turn.

•        Exhaust gases are pushed out polluting the atmosphere.

Merits and Demerits of 2-Stroke over 4-Stroke engines:

•        Merits

–      Power impulses are double in Given Time

–      Greater Power – Smaller Engine Size

–      Flywheel size is smaller –Idle strokes are reduced

–      No Valves and Valve operating Mechanisms

–      Easy to maintain

–      Less Initial Cost

–      Greater Mechanical efficiency

•        Demerits

–      Ring rotation to be prevented: damage the ports

–      Short Circuiting of Air Fuel Mixture

–      Ports weaken the cylinder wall

–      Crankcase must be airtight

–      Scavenging is difficult

–      Supercharging not possible