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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. LECTURE OUTLINE. Review

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Mae 4261 air breathing engines

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


Lecture outline
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


Fluid mechanics derivation of thrust equation
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
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
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
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 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
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


Ge j85

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 J85



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)

P&W F100 and 229


Unducted fan a 30
UNDUCTED FAN, a ~ 30

ANTONOW AN 70 PROPELLER DETAIL



Efficiency summary
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



Commercial and military engines approx same thrust approx correct relative sizes
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
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
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
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 35 000 ft 0 8 mach number standard day wisler
SUBSONIC ENGINE SFC TRENDS Royce](35,000 ft. 0.8 Mach Number, Standard Day [Wisler])


Aeroengine core power evolution dependence on turbine entry temperature meece koff
AEROENGINE CORE POWER EVOLUTION: Royce]DEPENDENCE ON TURBINE ENTRY TEMPERATURE [Meece/Koff]



Air breathing propulsion systems ramjets turbojets turbofans

AIR-BREATHING PROPULSION SYSTEMS Royce]RAMJETSTURBOJETSTURBOFANS

Daniel R. Kirk

Assistant Professor

Mechanical and Aerospace Engineering Department

Florida Institute of Technology


Ramjets
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
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 see inlet slides for more details
TURBOJET TRENDS: IN-CLASS EXAMPLE Royce](SEE INLET SLIDES FOR MORE DETAILS)


Turbojet trends homework 3 part 1 t t4 1600 k p c 25 t 0 220 k
TURBOJET TRENDS: HOMEWORK #3, PART 1 Royce]Tt4 = 1600 K, pc = 25, T0 = 220 K


Turbojet trends homework 3 part 2a t t4 1400 k t 0 220 k m 0 0 85 and 1 2
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 t t4 1400 k and 1800 k t 0 220 k m 0 0 85
TURBOJET TRENDS: HOMEWORK #3, PART 2b Royce] Tt4 = 1400 K and 1800 K, T0 = 220 K, M0 = 0.85


Turbofan summary
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 example1
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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