The design of the inlet for a turbojet engine is a critical aspect of optimizing its performance. Turbojet engines are air-breathing jet engines that compress air, mix it with fuel, combust it, and then expel the exhaust gases to generate thrust.
The cross-sectional area of the inlet is an important parameter, and it is typically designed to efficiently capture and compress air for combustion. The relationship between the cross-sectional areas and velocities at the inlet and exit for a turbojet engine can be described by the continuity equation:
where:
-  and  are the cross-sectional areas at the nozzle entrance and exit, respectively,
-  and  are the velocities at the nozzle entrance and exit, respectively.
which gives
where,
- A1Â is the Area of Nozzle Inlet in m2
- A2Â is the Area of Nozzle Exhaust in m2
- V1Â is the Inlet air Velocity in m/s
- V2Â is the Exhaust Air Velocity in m/s