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MAE 4261: AIR-BREATHING ENGINESPowerPoint Presentation

MAE 4261: AIR-BREATHING ENGINES

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### MAE 4261: AIR-BREATHING ENGINES

### AIR-BREATHING PROPULSION SYSTEMS Royce]RAMJETSTURBOJETSTURBOFANS

Air-Breathing Engine Performance Parameters

and Future Trends

Mechanical and Aerospace Engineering Department

Florida Institute of Technology

D. R. Kirk

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]

- Goal: Look at how efficiently the propulsion system converts one form of energy to another on its way to producing thrust
- Implications of Propulsive Efficiency for Engine Design
- Trends in Thermal and Propulsive Efficiency

FLUID MECHANICS: DERIVATION OF THRUST EQUATION

Chemical

Energy

Kinetic

Energy

Thermal

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

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

P-V DIAGRAM REPRESENTATION

- Thermal efficiency of Brayton Cycle, hth=1-T1/T3
- Function of temperature or pressure ratio across inlet and compressor

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.

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

TRENDS TO HIGHER BYPASS RATIO

1995: Boeing 777, FAA Certified

1958: Boeing 707, United States' first commercial jet airliner

Similar to PWJT4A: T=17,000 lbf, a ~ 1

PW4000-112: T=100,000 lbf , a ~ 6

J85-GE-1 - 2,600 lbf (11.6 kN) thrust

J85-GE-3 - 2,450 lbf (10.9 kN) thrust

J85-GE-4 - 2,950 lbf (13.1 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-13 - 4,080 lbf (18.1 kN), 4,850 lbf (21.6 kN) thrust

J85-GE-15 - 4,300 lbf (19 kN) thrust

J85-GE-17A - 2,850 lbf (12.7 kN) thrust

J85-GE-21 - 5,000 lbf (22 kN) thrust

GE J85Type: 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)

P&W F100 and 229UNDUCTED FAN, a ~ 30

ANTONOW AN 70 PROPELLER DETAIL

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

PROPULSIVE EFFICIENCY AND SPECIFIC THRUST AS A FUNCTION OF EXHAUST VELOCITY

Conflict

COMMERCIAL AND MILITARY ENGINES EXHAUST VELOCITY(APPROX. SAME THRUST, APPROX. CORRECT RELATIVE SIZES)

- 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 ↓

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 ↑

P&W 119 for F- 22, T~35,000 lbf, a ~ 0.3

EXAMPLE: SPECIFIC IMPULSE EXHAUST VELOCITY

SSME

PW4000 Turbofan

- Airbus A310-300, A300-600, Boeing 747-400, 767-200/300, 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

- 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

OVERALL PROPULSION SYSTEM EFFICIENCY Royce]

- 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

FUEL CONSUMPTION TREND Royce]

- 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

PW4084

JT9D

Future

Turbofan

PW4052

NOTE: No Numbers

1950

1960

1970

1980

1990

2000

2010

2020

Year

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

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

Daniel R. Kirk

Assistant Professor

Mechanical and Aerospace Engineering Department

Florida Institute of Technology

RAMJETS Royce]

- 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

Cycle analysis employing general form of mass, momentum and energy

Energy (1st Law) balance across burner

TURBOJET SUMMARY Royce]

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

TURBOJET TRENDS: IN-CLASS EXAMPLE Royce](SEE INLET SLIDES FOR MORE DETAILS)

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

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

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

TURBOFAN SUMMARY Royce]

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

TURBOFAN TRENDS: IN-CLASS EXAMPLE Royce]

Improvement over turbojet:

4 – 2.4 → 66% at Mach 1

8 – 3.3 → 142% at Mach 0

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