The cross-sectional area of the nozzle exhaust for a turbojet engine is a critical parameter in the design and performance of the engine. The nozzle is responsible for expanding and accelerating the high-speed exhaust gases produced during combustion in the engine. The design of the exhaust nozzle is crucial for achieving the desired thrust and efficiency.
For a turbojet engine, the exhaust nozzle is typically designed to accelerate the exhaust gases to achieve the desired exit velocity, maximizing thrust efficiency. The specific details of the nozzle design depend on various factors, including the engine’s operating conditions, mission requirements, and the desired performance characteristics.
The relationship between the cross-sectional areas and velocities at the throat and exit of a rocket or jet engine nozzle 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