A turbojet squeezes air, burns fuel in it, and throws the hot gas out the back. Follow the air from the inlet through the compressor, combustor and turbine, and out of the nozzle.
A turbojet is the simplest kind of jet engine. It takes in air, compresses it, burns fuel in it, uses some of the hot gas to keep itself running, and throws the rest out the back as a fast jet. All of the thrust comes from that jet of exhaust, which is why it is called a turbojet rather than a turbofan.
Outside, a turbojet is just a tube with a hole at each end. The whole story — how air is captured, squeezed, burned and expanded — is on the inside, where four sections sit in a row along one shaft.
As the compressor turns, it pulls air in through the inlet at the front. The smooth mouth of the inlet lets the air arrive without stirring it up, because the engine works best on a steady, even stream.
The compressor is a series of blade rows, each turning the air and passing it to the next in a slightly smaller space. Squeezing the air raises its pressure many times over. High-pressure air burns with far more force than air at everyday pressure, so this step is what makes the rest of the engine worthwhile.
Fuel is sprayed into the compressed air and ignited in the combustor. The result is a stream of very hot, high-pressure gas, which now holds the energy the engine will use — first to run itself, and then to fly.
The hot gas rushes over the turbine, spinning it like a windmill. The turbine does not make the thrust; it takes just enough energy to turn the shaft, which reaches forward to the compressor. In this way the engine keeps its own compressor going.
What is left of the hot gas leaves the turbine and enters the converging exhaust nozzle. As the duct narrows, the gas speeds up, and the fast jet leaving the engine is the thrust that pushes the aircraft along.
Burning compressed air releases far more useful energy than burning air at everyday pressure. Raising the pressure first lets each kilogram of air carry much more work to the turbine and nozzle.
No. The turbine mainly spins the compressor; it takes just enough energy to keep the engine turning. The thrust comes from the hot gas left over, which is accelerated out of the exhaust nozzle.
The compressor only builds pressure when it is already turning quickly, so a turbojet has to be spun up by a starter or another engine before it can sustain itself.
It connects the turbine at the back to the compressor at the front, so the energy taken from the hot gas turns the compressor without a separate motor.
No. It needs air to burn and to push backwards, so it only works inside the atmosphere. A rocket carries its own oxidizer for exactly this reason.