An Internal Combustion Engine (IC Engine) is a type of combustion engine that converts chemical energy into thermal energy, to produce useful mechanical work. In an IC engine, combustion chamber is an integral part of the working fluid circuit.

Principle of operation:

Air-fuel mixture in the combustion chamber (inside the cylinder) is ignited, either by a spark plug (in case of Spark Ignition Engines) or by compression (in case of Compression Ignition engines). This ignition produces tremendous amount of heat and pressure inside the cylinder. This induces reciprocating motion in the piston.

Power of the piston is transmitted to a crankshaft which undergoes rotary motion. The rotary motion is ultimately transmitted to the wheels of the vehicle, via a transmission system, to produce propulsion in the vehicle.

As the combustion takes place internally inside the cylinder (a part of working fluid circuit), the engine is called internal combustion engine.

The working pressure and temperature inside the cylinder of an IC engine is very high. The efficiency of IC engines is about 35-40 percent.