AERO ENGINE ch2-1.ppt
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Transcript of AERO ENGINE ch2-1.ppt
1
Previous lectures
• Chapter 1 Theoretical basis–Thermodynamics
–Aerodynamics
2
Chapter 2Principle of Gas Turbine Engine
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Chapter 2Principle of Gas Turbine Engine
• §2.1 Thermodynamic cycles of gas turbine engines– 1. Ideal cycle – 2. Real cycle
• §2.2 Thrust– 1. Propulsion power and propulsion efficiency– 2. Total efficiency– 3. Parameter evolution along flow passage– 4. Thrust distribution and delivery in components
• §2.3 Gas engine performance and specifications– 1. Performance characteristics – 2. Specifications – 3. Future development
• §2.4 Variations of Aircraft engines
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Turbofan engine with afterburner
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5 components of turbo engines
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Compressor
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8
Combustion chamber
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Turbine
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§2.1 Thermodynamic cycles of gas turbine engines
• 1. Ideal cycle (Brayton cycle)
– 0-2 Isentropic compression– 2-3 Isobar heating– 3-9 Isentropic expansion– 9-0 Isobar cooling
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1. Ideal cycle (Cont’d)
• 0-2 Isentropic compression
– Diffuser and compressor– 0-1 speed pressure rise. 0 atmosphere
condition. Add dynamic energy to substance and to increase pressure to 1. Area 011'0'0 presents dynamic energy difference.
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1. Ideal cycle (Cont’d)
• 0-2 Isentropic compression
– 1-2: compressor. Pressure from 1 to 2, work added is the area 122'1'1.
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Bernoulli function
02
1 21
22
2
1 fWWvv
dp
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1. Ideal cycle (Cont'd)
• 2-3 Isobar heating
– Combustion chamber– Burn ideally kerosene at constant pressure in
combustion chamber and substance properties unchanged.
– Total temperature T2* T3
* 。
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1. Ideal cycle (Cont'd)
• 3-9 Isentropic expansion
– Turbine and nozzle– 3-4 presents expansion in turbine, heatme
chanical energy giving to compressor. Area 344'2'3=Area 122'1'1, total pressure p3
*p4*.
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1. Ideal cycle (Cont'd)
• 3-9 Isentropic expansion
– 4-9 complete expansion in exhaust system. Heat changes kinetic energy in substance, exits from the nozzle.
– As diffuser, kinetic energy change can be seen as output work.
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1. Ideal cycle (Cont'd)
• 9-0 Isobar heat release
– Dash line, accomplished in atmosphere. This process is unavoidable, The cycle is closed.
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1. Ideal cycle (Cont'd)
• Specific heat added in the cycle
• Specific heat release
• Specific work in the cycle
)( *2
*31 TTcq p
)( 092 TTcq p
21 qqW
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1. Ideal cycle (Cont'd)
• Thermal efficiency in the cycle
Where pressure ratio
11
21
1
11
q
q
Wt
0
*2p
p
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1. Ideal cycle (Cont'd)
• Cycle work as mechanical energy
if WT=WC
2 29 0
2 2T C
v vW W W
2
20
29 vv
W
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§2.1 Thermodynamic cycles of gas turbine engines
• 2. Real cycle
– 0-2 Compression (non isentropic)– 2-3 Heating (non isobar)– 3-9 Expansion (non isentropic)– 9-0 Isobar heat release
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2. Real cycle (Cont'd)
• 0-2 Compression– Stagnation in diffuser and compression in
compressor have many types of losses. – Non isentropic and n >
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2. Real cycle (Cont'd)
• 2-3 Non isobar heating– Existing flow losses and thermal
resistance losses lows the pressure in combustion chamber.
– Composition of substance changes.
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2. Real cycle (Cont'd)
• 3-9 Expansion– There are always losses in turbine and
nozzle.
– Non isentropic and n <
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2. Real cycle (Cont'd)
• Heat added, area 2’233’2’
• Heat released, area 0’099’0’
cp’ gas specific heat
)( *2
*31 TTcq p
)( 09'
2 TTcq p
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2. Real cycle (Cont'd)
• Efficiency
• Work
21 qqW
1
21
q
qqt
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2. Real cycle (Cont'd)
• If T3* lower, q1=q2, then t=0, no output work.
• Work can be presented by mechanical energy, same as ideal cycle:
2
20
29 vv
W
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2. Real cycle (Cont'd)
• Under the same pressure ratio and the same T3*, work is smaller in real cycle than ideal cycle.
• Note that area in diagram T-s is heat, not work.
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2. Real cycle (Cont'd)
• If not take account of composition change and mass flow increase, differences between real cycle and ideal cycle are:– Friction and flow losses
– Total pressure loss
– Heating resistance
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2. Real cycle (Cont'd)
• Finally, in nozzle gas kinetic energy is smaller, velocity of air jet is smaller.
• To improve engine’s efficiency, use the components of high efficiency and high performance.
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§2.2 Thrust generation
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§2.2 Thrust generation
• Turbo-engine thrust overcomes airplane drag or accelerates airplane.
• Usually called effective thrust.
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§2.2 Thrust generation (Cont’d)
• Thrust = momentum of air + static pressure differences
• Usually, p9≈p0 and neglecting fuel flow, then
)( 09 vvqF m
)(
)()(
09909
00009909
ppAvqvq
ppAppAvqvqF
mmg
mmg
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§2.2 Thrust generation (Cont'd)
• 1. Propulsion power and efficiency– Propulsion power Fv0 , v0 flying speed
or air velocity in engine inlet.
– Thermal cycle of engine produces power
2
20
29 vv
qP m
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§2.2 Thrust generation (Cont'd)
– Since thrust , propulsion efficiency (percentage of propulsion power in thermal cycle power)
( 2-16 )
– Work provided by engine are divided into 2 parts: one pushes airplane forward; another jets gas backward. The second part is (/kg air)
)( 09 vvqF m
0
920
29
0
1
2
2 vvvv
q
Fv
m
P
2
)()(
2
209
009
20
29 vv
vvvvv
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§2.2 Thrust generation (Cont'd)
• 2. Total efficiency– Propulsion power over burning fuel heat
t Thermal eff (0.25~0.40), P propulsion eff (0.50~0.75), total eff (0.20~0.30)
– How to improve total efficiency• T3*
• Bypass ratio
Ptmqq
Fv
1
00
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§2.2 Thrust generation (Cont'd)
• 3. Parameter evolution along air passage
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§2.2 Thrust generation (Cont'd)
• 4. Thrust distribution in the components
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4. Thrust distribution (Cont'd)
WP6 bearing configuration ( 1-2-0 )
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Summary
• §2.1 Thermodynamic cycles of gas turbine engines1. Ideal cycle
2. Real cycle
• §2.2 Thrust generation1. Propulsion power and efficiency
2. Total efficiency
3. Parameter evolution along air passage
4. Thrust distribution in the components