An engine is a power generating machine, which converts potential energy of the fuel into heat energy and then into motion. It produces power and also runs on its own power. The engine’s power is generated by burning the fuel in a self-regulated and controlled Combustion’ process. The combustion process involves many sub-processes; which burn the fuel efficiently to effect the smooth running of the engine

Petrol Engine

A petrol engine (known as a gasoline engine in American English) is an internal combustion engine with spark-ignition, designed to run on petrol (gasoline) and similar volatile fuels. The first practical petrol engine was built in 1876 in Germany by Nikolaus August Otto.  In most petrol engines, the fuel and air are usually pre-mixed before compression (although some modern petrol engines now use cylinder-direct petrol injection). The pre-mixing was formerly done in a carburetor, but now it is done by electronically controlled fuel injection, except in small engines where the cost/complication of electronics does not justify the added engine efficiency.

How an Engine Works?

The Heat Energy is converted into Kinetic Energy in the form of ‘Reciprocating Motion’. The expansion of heated gases and their forces act on the engine pistons, pushing them downwards; resulting in reciprocating motion of pistons. The reciprocating motion of the piston enables the crank-shaft to rotate and finally gets converted into the ‘Rotary motion‘ and passed on to wheels.

Operation / Working Principle:

The conventional internal combustion engine operates on two basic principals –

  1. Otto Cycle &
  2. Diesel Cycle

What is ‘Otto Cycle’?

Otto Cycle is also known as Four-Stroke Spark-Ignition Cycle. It was named after German engineer Nikolaus Otto, who invented, developed and patented first Four-Stroke petrol engine. The Four-Stroke petrol engine works on the following cycle –

  1. Suction Stroke–
    with pistons moving downwards and opening of the inlet valve creates suction of the air-fuel mixture.
  2. Compression Stroke– With closing of Inlet valve, the area above the piston gets closed. The piston moves up resulting in compression of the air-fuel mixture in a confined space.
  3. Power Stroke – These forces again push the pistons downwards resulting in their reciprocating motion.
  4. Exhaust Stroke– On their way up, the pistons push the exhaust gases above them thru’ the exhaust valve which opens during the exhaust stroke.

Combustion Process – At this stage a spark is fired by the spark-plug resulting in instantaneous burning of petrol resulting in an explosion. This causes heat to release resulting in generation of expanding forces known as power.


Petrol engines may be air-cooled, with fins (to increase the surface area on the cylinders and cylinder head); or liquid-cooled, by a water jacket and radiator. The coolant was formerly water, but is now usually a mixture of water and either ethylene glycol or propylene glycol.

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