Petrol Engine

• Developed by Otto in 1876, hence known as Otto Engine.
• Consists of cylinder fitted with the piston.
• Cylinder is provided with inlet and outlet valve.
• Opening and closing of valve is controlled by movement of piston.
• Is a four stroke IC engine and uses a mixture of petrol and air.

Working of Petrol Engine

a) Suction Stroke:

• Inlet valve is opened and the air petrol mixture is sucked into the cylinder by the outward motion of the piston.

b) Compression stroke:

• Both the inlet and outlet valve are closed.
• The mixture undergoes adiabatic compression and its volume is reduced to about 1/5^th of the original volume.
• Hence, the temperature of mixture is raised to 600 ⁰

C) Working stroke:

• Here, inlet and outlet valve remain closed.
• A Spark is produced in spark plug and the compressed mixture of petrol vapour and air ignites.
• Temperature rises to 2000 ⁰C and pressure of 15 atm is developed inside the cylinder.
• The piston is pushed down and the shaft rotates

D) Exhaust Stroke:

• The outlet opens and the burnt-out gases are exhausted out to the atmosphere.

Efficiency of petrol engine

• It is calculated by:

η= W/Q₁ = (Q₁-Q₂)/Q₁