What type of engine is defined as one where aircraft propellers are turned by a turbine?

A turboprop engine is specifically designed to turn aircraft propellers using the power generated by a turbine. In a turboprop system, a gas turbine engine produces exhaust gases that drive the turbine, which in turn is connected to a reduction gearbox. This gearbox reduces the high rotational speed of the turbine to a more appropriate speed for efficient propeller operation. This type of engine combines the high speed and efficiency of a turbine while utilizing the thrust produced by propellers for improved performance at lower speeds, making it particularly effective for regional and commuter aircraft.

The other types of engines mentioned do not operate by turning propellers with a turbine. A reciprocating engine, for instance, uses pistons to generate thrust rather than a turbine. Turbofan engines generate thrust primarily by accelerating large amounts of air through a fan and the engine core but do not use propellers. Ramjets and scramjets operate on a fundamentally different principle, relying on high-speed air intake and combustion without using rotating parts to produce thrust.