The aircraft diesel engine or aero diesel is a diesel-powered aircraft engine. They were used in airships and tried in aircraft in the late 1920s and 1930s, but were never widely adopted until recently. Their main advantages are their excellent specific fuel consumption, the reduced flammability and somewhat higher density of their fuel, but these have been outweighed by a combination of inherent disadvantages compared to gasoline-fueled or turboprop engines. The ever-rising cost of avgas and doubts about its future availability have spurred a resurgence in aircraft diesel engine production in the early 2010s.

An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Aircraft using power components are referred to as powered flight. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years many small UAVs have used electric motors.