A jet engine is an internal combustion engine that provides propulsion by utilizing Newton’s third law of motion. In general, it works by sucking in and compressing air with powerful turbines that rotate within the engine at extremely high speeds. These types of jet engines are commonly known as airbreathing jet engines. There are also other forms of jet engines that use means other than air in order to provide propulsion but still operate under the same principle. Jet engines are popularly known to be used by aircraft.
An aircraft jet engine [Image Courtesy of NAMTEC]
There are various types of jet engines all of which operate based on the principle of jet propulsion. These are briefly discussed below.
Airbreathing Jet Engine
Airbreathing jet engines achieve propulsion by drawing air in and heating it with a compressor and then subsequently ejecting a jet of hot exhaust gases. Airbreathing jet engines have various designs such as Turbine Powered, which include turbojet, turbofan, turboprop, turboshaft and propfan, and Ram Powered such as ramjet and scramjet.
Airbreathing Jet Engine [Image Courtesy of Wikipedia]
The basic principles of operation of a Rocket engine is the same as the jet engine. The only difference is that the Rocket engine does not require atmospheric oxygen for its operation. All the required components are carried onboard, thereforethey are well suited for uses in space and the high atmosphere.
Rocket Engine [Image Courtesy of NASA]
Water Jet Engine
This type of propulsion is mainly used by the marines. Instead of using air, this system uses a jet of water for its propulsion. In order to do this, the engine either constitutes of a ducted propeller with a nozzle or a centrifugal compressor and a nozzle.
Water Jet Engine [Image Courtesy of Correct Craft Fan]
For a better perspective, here is an animated video of how a jet engine works. Enjoy!