Which engine type works by converting straight-line motion to rotary motion with crankshaft and pistons?

The correct answer, reciprocating engine, is based on its fundamental design and operation. This type of engine utilizes pistons that move in a straight line within cylinders, driven by the combustion of fuel and air. As the pistons move up and down due to combustion pressure, this linear motion is translated into rotary motion through the crankshaft. The crankshaft then converts this motion to rotate the propeller or drive the vehicle.

Reciprocating engines are common in many applications, including automobiles and smaller aircraft, because of their effective and efficient conversion of energy from fuel into mechanical work. This principle makes them distinct from other engine types, wherein alternative mechanisms like electric motors or turbine systems operate differently and do not utilize straight-line motion to produce rotary motion in the same way.

Turboprop engines, for instance, combine turbine engine technology with a propeller, while ramjets and scramjets rely on high-speed airflow for propulsion without any moving parts. Hydraulic systems, on the other hand, focus on the transmission of power through fluid pressure and are not related to the conversion of linear motion into rotary motion.