Chap 4 : Engine Performance

Question 1

What are the parameters of an engine flight envelope ?

Answer 1

Altitude, Mach number, airspeed and temperature

Question 2

What is a flight envelope ?

Answer 2

It représentés the rangé of conditions in which an aircraft and its engine can safely operate

Question 3

What are the flame-out conditions for a flight envelope ?

Answer 3

Oxygen deficiency (high altitude)
Foreign object damage
Extreme weather conditions
Fuel starvation
Compressor stall

Question 4

What’s the ram effect ?

Answer 4

Deceleration of the incoming flow in the entry of the engine
=> Increasing of pressure & temperature and decreasing of velocity

Question 5

What are the purpose & the effects of an afterburner ?

Answer 5

Purpose : increase the thrust of a jet engine

Effects :
-Increase more the temperature at the exit and the max enthalpy of the cycle.
-Big fuel consumption until Mach=2.4 after more fuel efficient with an afterburnan than without.

Question 6

What’s the specific net work ? (Wn)

Answer 6

Specific heat added - absolut specific heat removed
= Kinetic energy at nozzle exit - kinetic energy added by forward speed of aircraft

Question 7

What’s the purpose of a recuperator and an inter-cooler ?

Answer 7

Recuperator : to extract the heat in the nozzle and put it before the CC

Inter-cooler : to reduce the temperature of the air before the HPC => decrease the work input required for compression

Question 8

What are the characteristic parameters of an engine ?

Answer 8

Specific thrust
Thrust to fuel ratio (=1/specific fuel consumption)
Thrust to weight ratio
Specific net work
Net power
Aircraft propulsive power
Thermal efficiency
Propulsive efficiency