The turbojet and the ramjet use much fuel. The turboprop and turbofan use less fuel. All four engines produce more thrust than a normal propeller driven aircraft. All four engines have the 5 components described before: an inlet, a compressor, a combustor, a turbine, and an exit nozzle.

An afterburner can be added to get more power (thrust). However, the afterburner uses a lot of fuel and can only be used a short time.

Fighter planes and some business jets need to go faster than the speed of sound (Mach 1.0). The turbojet engine can do this, so it is put into this kind of airplane.

Turboprop:

The turboprop engine uses the same components as the turbojet. This engine produces two thrusts using the jet principle. The first thrust comes from a large propeller driven by the turbine. There is also a jet exhaust pushing the airplane forward.

The turboprop is faster than a normal propeller driven airplane, but slower than a turbojet. A turboprop must fly slower than the speed of sound. Thrust from the propeller and a large gearbox (running the propellers at high speed) help keep the fuel consumption low. Slower airplanes use this engine. The design of a turboprop engine is shown below.

Turbofan:

The turbofan has an internal (inside) propeller or fan. This propeller, or fan is inside a duct or tube. This makes much more thrust than the turboprop that has outside propellers. This allows the turbofan airplane to go almost the speed of sound, up to Mach .9. The figure below shows the design of a turbofan engine.

This makes it faster than the turboprop, but slower than the turbojet. This engine also produces two thrusts, one from the fan and one from the jet exhaust. The gear box for the fan is much smaller than the turboprop gear box. This means there is less chance for something to break.

The turbofan engine is put into high-speed, subsonic commercial airplanes.

Ramjets:

This engine ONLY works at speeds above Mach 1.0. An airplane with this engine must use a turbojet engine to fly above Mach 1.0, then the ramjet takes over. The ramjet engine can fly up to Mach 6.0. The design of a ramjet engine is shown below.