1. MAE 4261: AIR-BREATHING ENGINES
Air-Breathing Engine Performance Parameters
and Future Trends
Mechanical and Aerospace Engineering Department
Florida Institute of Technology
D. R. Kirk

2. LECTURE OUTLINE Review
General expression that relates the thrust of a propulsion system to the net changes in momentum, pressure forces, etc.
Efficiencies
Goal: Look at how efficiently the propulsion system converts one form of energy to another on its way to producing thrust
Overall Efficiency, hoverall
Thermal (Cycle) Efficiency, hthermal
Propulsive Efficiency, hpropulsive
Specific Impulse, Isp [s]
(Thrust) Specific Fuel Consumption, (T)SFC [lbm/hr lbf] or [kg/s N]
Implications of Propulsive Efficiency for Engine Design
Trends in Thermal and Propulsive Efficiency

3. FLUID MECHANICS: DERIVATION OF THRUST EQUATION
Chemical
Energy
Thermal
Energy
Kinetic
Energy
Flow through engine is conventionally called THRUST
Composed of net change in momentum of inlet and exit air
Fluid that passes around engine is conventionally called DRAG

4. THERMODYANMICS: BRAYTON CYCLE MODEL
1-2: Inlet, Compressor and/or Fan: Adiabatic compression with spinning blade rows
2-3: Combustor: Constant pressure heat addition
3-4: Turbine and Nozzle: Adiabatic expansion
Take work out of flow to drive compressor
Remaining work to accelerate fluid for jet propulsion
Thermal efficiency of Brayton Cycle, hth=1-T1/T2
Function of temperature or pressure ratio across inlet and compressor

5. P-V DIAGRAM REPRESENTATION
Thermal efficiency of Brayton Cycle, hth=1-T1/T3
Function of temperature or pressure ratio across inlet and compressor

6. EXAMPLE OF LAND-BASED POWER TURBINE: GENERAL ELECTRIC LM5000
Modern land-based gas turbine used for electrical power production and mechanical drives
Length of 246 inches (6.2 m) and a weight of about 27,700 pounds (12,500 kg)
Maximum shaft power of 55.2 MW (74,000 hp) at 3,600 rpm with steam injection
This model shows a direct drive configuration where the LP turbine drives both the LP compressor and the output shaft. Other models can be made with a power turbine.

7. BYPASS RATIO: TURBOFAN ENGINES
Bypass Air
Core Air
Bypass Ratio, B, a:
Ratio of bypass air flow rate to core flow rate
Example: Bypass ratio of 6:1 means that air volume flowing through fan and bypassing core engine is six times air volume flowing through core

8. TRENDS TO HIGHER BYPASS RATIO
1958: Boeing 707, United States' first commercial jet airliner
1995: Boeing 777, FAA Certified
Similar to PWJT4A: T=17,000 lbf, a ~ 1
PW : T=100,000 lbf , a ~ 6

9. GE J85 J85-GE-1 - 2,600 lbf (11.6 kN) thrust
J85-GE-5 - 2,400 lbf (10.7 kN) thrust, 3,600 lbf (16 kN) afterburning thrust
J85-GE-5A - 3,850 lbf (17.1 kN) afterburning thrust
J85-GE ,080 lbf (18.1 kN), 4,850 lbf (21.6 kN) thrust
J85-GE ,300 lbf (19 kN) thrust
J85-GE-17A - 2,850 lbf (12.7 kN) thrust
J85-GE ,000 lbf (22 kN) thrust

10. TURBOJET / MODERATE BYPASS TURBOFAN

11. P&W F100 and 229 P&W 229 Overview Type: Afterburning turbofan
Length: 191 in (4,851 mm)
Diameter: 46.5 in (1,181 mm)
Dry weight: 3,740 lb (1,696 kg)
Components
Compressor: Axial compressor with 3 fan and 10 compressor stages
Bypass ratio: 0.36:1
Turbine: 2 low-pressure and 2 high-pressure stages
Maximum Thrust:
17,800 lbf (79.1 kN) military thrust
29,160 lbf (129.6 kN) with afterburner
Overall pressure ratio: 32:1
Specific fuel consumption:
Military thrust: 0.76 lb/(lbf·h) (77.5 kg/(kN·h))
Full afterburner: 1.94 lb/(lbf·h) (197.8 kg/(kN·h))
Thrust-to-weight ratio: 7.8:1 (76.0 N/kg)

12. ANTONOW AN 70 PROPELLER DETAIL
UNDUCTED FAN, a ~ 30

13. “HYBRID” DUCTED FAN + TURBOJET

14. EFFICIENCY SUMMARY Overall Efficiency What you get / What you pay for
Propulsive Power / Fuel Power
Propulsive Power = TUo
Fuel Power = (fuel mass flow rate) x (fuel energy per unit mass)
Thermal Efficiency
Rate of production of propulsive kinetic energy / fuel power
This is cycle efficiency
Propulsive Efficiency
Propulsive Power / Rate of production of propulsive kinetic energy, or
Power to airplane / Power in Jet

15. PROPULSIVE EFFICIENCY AND SPECIFIC THRUST AS A FUNCTION OF EXHAUST VELOCITY
Conflict

16. COMMERCIAL AND MILITARY ENGINES (APPROX. SAME THRUST, APPROX
COMMERCIAL AND MILITARY ENGINES (APPROX. SAME THRUST, APPROX. CORRECT RELATIVE SIZES)
GE CFM56 for Boeing 737 T~30,000 lbf, a ~ 5
Demand higher efficiency
Fly at lower speed (subsonic, M∞ ~ 0.85)
Engine has large inlet area
Engine has lower specific thrust
Ue/Uo → 1 and hprop ↑
Demand high T/W
Fly at high speed
Engine has small inlet area (low drag, low radar cross-section)
Engine has high specific thrust
Ue/Uo ↑ and hprop ↓
P&W 119 for F- 22, T~35,000 lbf, a ~ 0.3

17. EXAMPLE: SPECIFIC IMPULSE
PW4000 Turbofan
SSME
Space Shuttle Main Engine
T ~ 2,100,000 N (vacuum)
LH2 flow rate ~ 70 kg/s
LOX flow rate ~ 425 kg/s
Isp ~ 430 seconds
Airbus A , A , Boeing , /300, MD-11
T ~ 250,000 N
TSFC ~ 17 g/kN s ~ 1.7x10-5 kg/Ns
Fuel mass flow ~ 4.25 kg/s
Isp ~ 6,000 seconds

18. PROPULSIVE EFFICIENCY FOR DIFFERENT ENGINE TYPES [Rolls Royce]

19. OVERALL PROPULSION SYSTEM EFFICIENCY
Trends in thermal efficiency are driven by increasing compression ratios and corresponding increases in turbine inlet temperature
Trends in propulsive efficiency are due to generally higher bypass ratio

20. FUEL CONSUMPTION TREND
U.S. airlines, hammered by soaring oil prices, will spend a staggering $5 billion more on fuel in 2007 or even a greater sum, draining already thin cash reserves
Airlines are among the industries hardest hit by high oil prices
“Airline stocks fell at the open of trading Tuesday as a spike in crude-oil futures weighed on the sector”
JT8D
Fuel Burn
JT9D
PW4084
Future
Turbofan
PW4052
NOTE: No Numbers
1950
1960
1970
1980
1990
2000
2010
2020
Year

21. CRUISE FUEL CONSUMPTION vs. BYPASS RATIO

22. SUBSONIC ENGINE SFC TRENDS (35,000 ft
SUBSONIC ENGINE SFC TRENDS (35,000 ft. 0.8 Mach Number, Standard Day [Wisler])

23. AEROENGINE CORE POWER EVOLUTION: DEPENDENCE ON TURBINE ENTRY TEMPERATURE [Meece/Koff]

24. PRESSURE RATIO TRENDS (Jane’s 1999)

25. AIR-BREATHING PROPULSION SYSTEMS RAMJETS TURBOJETS TURBOFANS
Daniel R. Kirk
Assistant Professor
Mechanical and Aerospace Engineering Department
Florida Institute of Technology

26. RAMJETS
Cycle analysis employing general form of mass, momentum and energy
Energy (1st Law) balance across burner
Thrust performance depends solely on total temperature rise across burner
Relies completely on “ram” compression of air (slowing down high speed flow)
Ramjet develops no static thrust

27. TURBOJET SUMMARY
Cycle analysis employing general form of mass, momentum and energy
Turbine power = compressor power
How do we tie in fuel flow, fuel energy?
Energy (1st Law) balance across burner

28. TURBOJET TRENDS: IN-CLASS EXAMPLE

29. TURBOJET TRENDS: IN-CLASS EXAMPLE (SEE INLET SLIDES FOR MORE DETAILS)

30. TURBOJET TRENDS: HOMEWORK #3, PART 1 Tt4 = 1600 K, pc = 25, T0 = 220 K

31. TURBOJET TRENDS: HOMEWORK #3, PART 2a Tt4 = 1400 K, T0 = 220 K, M0 = 0
TURBOJET TRENDS: HOMEWORK #3, PART 2a Tt4 = 1400 K, T0 = 220 K, M0 = 0.85 and 1.2

32. TURBOJET TRENDS: HOMEWORK #3, PART 2b Tt4 = 1400 K and 1800 K, T0 = 220 K, M0 = 0.85

33. TURBOFAN SUMMARY Two streams: Core and Fan Flow
Turbine power = compressor + fan power
Exhaust streams have same velocity: U6=U8
Maximum power, tc selected
to maximize tf

34. TURBOFAN TRENDS: IN-CLASS EXAMPLE

35. TURBOFAN TRENDS: IN-CLASS EXAMPLE
Improvement over turbojet:
4 – 2.4 → 66% at Mach 1
8 – 3.3 → 142% at Mach 0

36. TURBOFAN TRENDS: IN-CLASS EXAMPLE