Definition
An engine that produces power by burning a fuel-and-air mixture inside a confined chamber within the engine itself, where the expanding gases from combustion act directly on a moving part such as a piston or turbine to generate mechanical work.
Plain English
An engine that burns fuel inside itself, and uses the force of that burning to push a part that turns the propeller or shaft.
Context Anchor
Seen in powerplant discussions, especially when describing piston aircraft engines and how they produce power.
Derivation
From Latin internus (inside) and combustio (burning up). The name simply highlights that the burning happens inside the engine — distinguishing it from earlier external-combustion engines like steam engines, where fuel was burned outside in a separate firebox to heat water.
Why Pilots Care
Most light aircraft rely on these engines for propulsion, so knowing their basic operation supports safe preflight checks and troubleshooting.
Intuition Check
Internal does not mean inside the airplane here. It means the fuel burns inside the engine's own chambers.
Example Sentence 1
The aircraft is powered by a four-cylinder internal-combustion engine driving a fixed-pitch propeller.
Example Sentence 2
Student pilots learn that an internal-combustion engine converts chemical energy from fuel into thrust through controlled explosions.