Properties of a turbojet engine For the case shown below a j

Properties of a turbojet engine

For the case shown below, a jet engine is sitting motionless on the ground prior to take-off. Air is entrained into the engine by the compressor. The inlet can be assumed to be adiabatic and frictionless. Also under-expanded nozzle can be assumed to be adiabatic but not frictionless. Considering the state of the gas within the inlet, prior to passage into the compressor, as state (1), and working in the reference frame of the motionless airplane: 1) Is P_15(>, =,, =,, =,

Solution

1.Pt5 < Pt4 because subsonic flow (M<1) pressure decreases with decrease in area because of expansion of gas as pressure energy gets converted to kinetic energy and velocity increases

2.Tt4 < Tt5 because during expansion in nozzle for subsonic flow temperature decreases

3.Pt3 > Pt2 because due to combustion of fuel pressure increases