Which type of jet engine does not have moving parts?

The correct answer is Ramjet. This type of jet engine operates under a principle that does not involve any moving parts, which distinguishes it from other jet engines such as turbojets and turbofans.

A ramjet relies on the forward motion of the aircraft to compress incoming air. As the aircraft moves, air enters the engine and gets compressed through the shape of the engine intake. The mixture of fuel with this compressed air is then ignited, and the high-pressure exhaust gases are expelled out of the engine, providing thrust. This design allows for simplicity and higher speeds, especially at supersonic speeds.

In contrast, turbojets and turbofans utilize rotating compressors and turbines that require moving parts to compress air and drive the engine cycle, which is not the case in ramjets. Pulsejets also have moving components related to their valving system, making them operationally different. Hence, ramjets stand out in their essential design as they achieve thrust without any mechanical moving components.