View
257
Download
2
Category
Tags:
Preview:
Citation preview
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
– 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, overall
• Thermal (Cycle) Efficiency, thermal
• Propulsive Efficiency, propulsive
– 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
• 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
ChemicalEnergy
ThermalEnergy
KineticEnergy
oe
eaeooee
VVmF
APPVmVmF
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, th=1-T1/T2
– Function of temperature or pressure ratio across inlet and compressor
P-V DIAGRAM REPRESENTATION
• Thermal efficiency of Brayton Cycle, th=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, :Ratio of bypass air flow rate to core flow rateExample: 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
1958: Boeing 707, United States' first commercial jet airliner 1995: Boeing 777, FAA Certified
PW4000-112: T=100,000 lbf , ~ 6Similar to PWJT4A: T=17,000 lbf, ~ 1
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
TURBOJET / MODERATE BYPASS TURBOFAN
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)
UNDUCTED FAN, ~ 30ANTONOW AN 70 PROPELLER DETAIL
“HYBRID” DUCTED FAN + TURBOJET
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
hm
TU
f
ooverall
hm
UmUm
f
ooee
thermal
22
22
propulsivethermaloverall
o
eooee
opropulsive
UUUmUm
TU
1
2
22
22
PROPULSIVE EFFICIENCY AND SPECIFIC THRUST AS A FUNCTION OF EXHAUST VELOCITY
o
epropulsive
U
U
1
2
1o
e
o U
U
Um
T
Conflict
COMMERCIAL AND MILITARY ENGINES(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 prop ↓ P&W 119 for F- 22, T~35,000 lbf, ~ 0.3
• 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 prop ↑
GE CFM56 for Boeing 737 T~30,000 lbf, ~ 5
EXAMPLE: SPECIFIC IMPULSE
• 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
PW4000 Turbofan SSME
PROPULSIVE EFFICIENCY FOR DIFFERENT ENGINE TYPES [Rolls Royce]
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
FUEL CONSUMPTION TREND
1950 1960 1970 1980 1990 2000 2010 2020
JT8D
JT9D
PW4052
PW4084Fue
l Bur
n
Year
FutureTurbofan
• 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”
NOTE: No Numbers
CRUISE FUEL CONSUMPTION vs. BYPASS RATIO
SUBSONIC ENGINE SFC TRENDS(35,000 ft. 0.8 Mach Number, Standard Day [Wisler])
AEROENGINE CORE POWER EVOLUTION: DEPENDENCE ON TURBINE ENTRY TEMPERATURE [Meece/Koff]
PRESSURE RATIO TRENDS (Jane’s 1999)
AIR-BREATHING PROPULSION SYSTEMS
RAMJETSTURBOJETSTURBOFANS
Daniel R. Kirk
Assistant Professor
Mechanical and Aerospace Engineering Department
Florida Institute of Technology
RAMJETS
• 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
1000
bMam
T hm
TU
foverall
0
Energy (1st Law) balance across burnerCycle analysis employing general form of mass, momentum and energy
TURBOJET SUMMARY
oco
ttco
oo
Mam
T
11
2
occo
too
Mam
T
1
11
1
20
0
000 1
ctoverall
am
TM
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
Plot of Non-Dimensional Thrust and Specific Impulse for Maximum Thrust Condition
Heating Value of Fuel = 4.3x107 J/kg, Specific Heat Ratio = 1.4, T0=200K
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 0.5 1 1.5 2 2.5 3
Flight Mach Number
Max
imu
m S
pec
ific
Th
rust
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
Sp
ecif
ic I
mp
uls
e, M
axim
um
T
hru
st,
s
Max Non-Dim Thrust: Theta_t=6Max Non-Dim Thrust: Theta_t=9Max Thrust Isp: Theta_t=6Max Thrust Isp: Theta_t=9
TURBOJET TRENDS: IN-CLASS EXAMPLE(SEE INLET SLIDES FOR MORE DETAILS)
Plot of Thrust Normalized by Compressor Inlet Area and Ambient Pressurevs. Flight Mach Number for Compressor Inlet Mach Number, M2=0.5
0
5
10
15
20
25
30
0 0.5 1 1.5 2 2.5 3
Flight Mach Number
Th
rust
No
rmal
ized
by
A2
and
P0
Theta_t=6
Theta_t=9
TURBOJET TRENDS: HOMEWORK #3, PART 1Tt4 = 1600 K, c = 25, T0 = 220 K
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
5.00
0 0.5 1 1.5 2 2.5 3
Mach Number
Sp
ec
ific
Th
rus
t
0%
20%
40%
60%
80%
100%
120%
Eff
icie
nc
y
Specific ThrustPropulsive EfficiencyThermal EfficiencyOverall Efficiency
TURBOJET TRENDS: HOMEWORK #3, PART 2a Tt4 = 1400 K, T0 = 220 K, M0 = 0.85 and 1.2
0.00
0.50
1.00
1.50
2.00
2.50
3.00
0 10 20 30 40 50
Compressor Pressure Ratio
Sp
ec
ific
Th
rus
t
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
Eff
icie
nc
y
Specific Thrust, M=0.85Specific Thrust, M=1.2Propulsive Efficiency, M=0.85Thermal Efficiency, M=0.85Overall Efficiency, M=0.85Propulsive Efficiency, M=1.2Thermal Efficiency, M=1.2Overall Efficiency, M=1.2
TURBOJET TRENDS: HOMEWORK #3, PART 2b Tt4 = 1400 K and 1800 K, T0 = 220 K, M0 = 0.85
0
0.5
1
1.5
2
2.5
3
3.5
4
0 10 20 30 40 50
Compressor Pressure Ratio
Sp
ec
ific
Th
rus
t
0%
10%
20%
30%
40%
50%
60%
70%
80%
Specific Thrust, Tt4=1400KSpecific Thrust, Tt4=1800 KPropulsive Efficiency, Tt4=1400 KThermal Efficiency, Tt4=1400 KOverall Efficiency, Tt4=1400 KPropulsive Efficiency, Tt4=1800 KThermal Efficiency, Tt4=1800 KOverall Efficiency, Tt4=1800 K
TURBOFAN SUMMARY
00 1
1
21
1
2MM
am
Tfo
co
ttco
o
00 1
1
21 M
am
Tf
o
00
2
max
11
1
1
21 M
am
T t
o
Two streams:Core and Fan Flow
Turbine power = compressor + fan powerExhaust streams have same velocity: U6=U8
Maximum power, c selectedto maximize f
TURBOFAN TRENDS: IN-CLASS EXAMPLE
Non-Dimensional Thrust vs. Flight Mach Numbert=6, To=200 K (PW4000 Series, ~ 5-6)
Higher of interest in range of Mo < 1 and lower of interest for supersonic transport
0
2
4
6
8
10
12
14
16
0 0.5 1 1.5 2 2.5 3Flight Mach Number, M0
No
n-D
ime
ns
ion
al T
hru
st
Bypass Ratio = 1Bypass Ratio = 5Bypass Ratio = 10Bypass Ratio = 20
TURBOFAN TRENDS: IN-CLASS EXAMPLE
Non-Dimensional Thrust vs. Flight Mach Numbert=6, To=200 K (PW4000 Series, ~ 5-6)
Higher of interest in range of Mo < 1 and lower of interest for supersonic transport
0
2
4
6
8
10
12
14
16
0 0.5 1 1.5 2 2.5 3Flight Mach Number, M0
No
n-D
ime
ns
ion
al T
hru
st
Bypass Ratio = 1Bypass Ratio = 5Bypass Ratio = 10Bypass Ratio = 20
Plot of Non-Dimensional Thrust and Specific Impulse for Maximum Thrust Condition
Heating Value of Fuel = 4.3x107 J/kg, Specific Heat Ratio = 1.4, T0=200K
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 0.5 1 1.5 2 2.5 3
Flight Mach Number
Max
imu
m S
pec
ific
Th
rust
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
Sp
ecif
ic I
mp
uls
e, M
axim
um
T
hru
st,
s
Max Non-Dim Thrust: Theta_t=6Max Non-Dim Thrust: Theta_t=9Max Thrust Isp: Theta_t=6Max Thrust Isp: Theta_t=9
Improvement over turbojet:4 – 2.4 → 66% at Mach 18 – 3.3 → 142% at Mach 0
TURBOFAN TRENDS: IN-CLASS EXAMPLE
Propulsive Efficiency vs. Flight Mach Numbert=6, To=200 K
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.5 1 1.5 2 2.5 3
Flight Mach Number, M0
Pro
pu
lsiv
e E
ffic
ien
cy
Bypass Ratio = 1Bypass Ratio = 5Bypass Ratio = 10Bypass Ratio = 20
Recommended