1. Parametric Cycle Analysis of Ideal Turbo Jet Engine
P M V Subbarao
Professor
Mechanical Engineering Department
Lecture - 8
Selection of Optimal Design Cruising Conditions….

2. Effect of Flight Mach Number on Compactness
t0,cc=4.5
r0p=20
r0p=30
r0p=10
r0p=5
r0p=3
r0p=2
r0p=1
Specific Thrust kN.s/kg
Mac

3. Effect of Flight Mach Number on Fuel Air Ratio
t0,cc=4.5
r0p 1 2 3 5 10 20 30
Mac

4. Effect of Flight Mach Number on Fuel Economy
t0,cc=4.5
r0p=1
r0p=2
r0p=3
TSFC kg/ kN.hr
r0p=5
r0p=10
r0p=20
r0p=30
Mac

5. Effect of Flight Mach Number on Fuel Air Ratio
t0,cc=4.5
r0p 1 2 3 5 10 20 30
Mac

6. Effect of Flight Mach Number on Propulsion Efficiency
t0,cc=4.5
r0p = 30
r0p =2
r0p = 5
Mac

7. Effect of Flight Mach Number on Thermal Efficiency
t0,cc=4.5
r0p
Mac

8. Effect of Flight Mach Number on Overall Efficiency
t0,cc=4.5 hO
r0p
Mac

9. Effect of Pressure Ratio on Compactness
Mac=0
t0,cc=4.5
Mac=0.5
Mac=1.0
Mac=1.5
Mac=2.0
Specific Thrust kN.s/kg
Mac=2.5
Mac=3.0 rp

10. Effect of Pressure Ratio on Fuel Economy
t0,cc=4.5
TSFC kg/ kN.hr
Mac rp

11. Effect of Pressure Ratio on Fuel Air Ratio
t0,cc=4.5 rp

12. Effect of Pressure Ratio on Propulsive Efficiency
t0,cc=4.5 rp

13. Effect of Pressure Ratio on Thermal Efficiency
t0,cc=4.5 rp

14. Effect of Pressure Ratio on Overall Efficiency
t0,cc=4.5 rp

15. Effect of Pressure Ratio on Compactness
Mac=0
t0,cc=4.5
Mac=0.5
Mac=1.0
Mac=1.5
Mac=2.0
Specific Thrust kN.s/kg
Mac=2.5
Mac=3.0 rp

16. Turbo Jet with Afterburner
inlet 1 2 7 5 3 6 4

17. Elevation of Temperature of the Jet:
After Burner : More Energy at Same Life

19. Minimum Jet Temperature
Jet Total Temperature :
Jet Static Temperature :

20. Characterization of AB Jet
Maximum obtainable Mach number of Jet

21. Performance of Jet Propulsive Power or Thrust Power: Specific Thrust S
Thrust Specific Fuel Consumption TSFC

22. AB & No AB
rp = 10
W AB
W AB
W/O AB
TSFC
Specific Thrust
W/O AB

23. Ideal Afterburning Turbojet Engine Performance : Specific Thrust Vs Compressor Pressure Ratio
2.5
Specific Thrust kN.s/kg
3.0 rp

24. Ideal Turbojet Engine Performance : Specific Thrust Vs Compressor Pressure Ratio
Maircraft
Specific Thrust kN.s/kg
Compressor Pressure Ratio : rp

25. Ideal Afterburning Turbojet Engine Performance : TSFC Vs Compressor Pressure Ratio
TSFC kg/ kN.hr rp

26. Effect of Pressure Ratio on Fuel Economy
Constant TIT
TSFC kg/ kN.hr
Mac rp

27. Ideal Afterburning Turbojet Engine Performance : TSFC Vs Compressor Pressure Ratio

28. Ideal Afterburning Turbojet Engine Performance : Efficiencies Vs Compressor Pressure Ratio

29. Summary of Turbojet Performance
A high compressor pressure ratio is desirable for subsonic flight for good specific thrust and low fuel consumption.
A special care must be used in selecting the compressor pressure ratio for the supersonic flight Mach number.
Rapid drop in specific thrust with pressure ratio at supersonic conditions.
There exist a pressure ratio for each Mach number of a supersonic flight, that gives maximum specific thrust.
The fuel air ratio decreases with increasing Mach number and compressor pressure ratio.
Propulsive efficiency increases with increasing Mach number.
Rapid fall in specific thrust under supersonic conditions is a serious concern.

30. Optimization of Turbojet Performance
P M V Subbarao
Professor
Mechanical Engineering Department
Better Deal for Compactness & Fuel Economy…

31. Optimum Compressor Pressure Ratio
At supersonic flight conditions, a maximum value of Specific thrust is Exhibited at certain compressor pressure ratio.
The value of pressure ratio to maximize the specific thrust at a given flight Mach number should be found by differentiation of specific thrust equation.
For Maximum Specific Thrust:

34. Optimum Compressor Pressure Ratio Vs Mach Number
W AB
r0p,opt
W/o AB
Mac

35. Optimal Turbojet Engine Performance
With After Burner
Specific Thrust kN.s/kg
TSFC kg/ kN.hr
Without After Burner
Mac

36. Energy Flow in Jet Engine
Energy input
Long distance travel demands high flight velocity.
High flight velocity leads to drop in compactness and fuel economy.
A Single Jet is blackmailing the jet engine !!!