Brifely explain the basic difference between turbojet engine

Brifely explain the basic difference between turbojet engine and ramjet engine. Also discuss the design limit of pressure ratio in the compressor. What will happen in the compressor if the pressure ratio exceeds design limit?

Solution

Both Turbo jet & Ram jet engines are basically air breathing enigines

The basic difference between the two is w.r.t how the ambient air enters the combustion chamber : A turbo jet uses a compressor (driven by the gas turbine) to suck & compress the ambient air before sending it over a combustion chamber. While the ramjet uses the motion of the engine or vehicle to pass the ambient air into the combustion chamber.

Increasing the compression ratio for a turbojet engine will increase the overall effieciney of the engines, however increasing the pressure ratio would also increase the temperature of the air that is compressed. Excessively high temperature of compressed air causes high thermal stresses leading to material failure risk to the final stage blades of the compresor. Hence the design limit of the pressure ratio is arrived at considering the maximum temperature which can be widthstood by the compressor blades without failing materially.