An internal combustion engine is a compact machine which converts the chemical energy contained in any given fuel into rotary mechanical energy, which is generally made available on a turning output shaft. The chemical energy contained in the fuel is first transformed into expanding thermal energy through combustion (explosion of fuel within a cylinder, with air inside it pushing down the piston). Then high-pressure hot gas suddenly originates from this combustion.
The hot gas expands against the mechanical mechanism of the engine, which is a piston attached to a rod. As the series of pistons in the engine are pushed downwards by successive explosion, the crankshaft is turned around by the moving piston rods. It is said that the rotating crankshaft is the engine output. The rotating crankshaft is connected to a transmission and power train to transmit the rotating mechanical energy to the desired end use, which could be the propulsion of a vehicle or the driving of an AC generator shaft to produce electricity.
Most internal combustion engines are reciprocating engines, which means they have pistons that move up and down, or back and forth, in their respective cylinders, which are usually arranged in line within the engine. Reciprocating engines can have one cylinder or many. These cylinders can be arranged in many different geometrical configurations. The first fairly practically internal combustion engine was invented by the French engineer Jean Joseph Etienne Lenoir around 1860. In the next decades, the German engineer, Nicolaus Otto, would build more efficient engines.
Below a cutaway drawing of a Chrysler 2.2-liter, four-piston, spark-ignition internal combustion engine.
