Gearbox Turbofan

Gas Power Power Cycle - Jet Propulsi Propulsion on Technolog Technology, y, A Case Study Study

Ideal Brayton Cycle Combustor 

Fuel

2

1-2 Isentropic compression 2-3 Constant pressure heat addition 3-4 Isentropic expansion 4-1 Constant pressure heat rejection

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3

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Compressor  Air 

4

1

Turbine

Products P

3

2

3

T

2 4 1

4

1 s

Ideal Brayton Cycle - 2 The thermal efficiency of the ideal Brayton cycle is  th



wnet qin

 1



wout  win qin

c p (T4  T 1 ) c p (T3  T2 )



qin  qout

1

1

qin

qout qin

T1 (T4 / T 1  1) T2 (T3 / T2    1)

 

 h4  h1  1   h3  h2 

equation (1)

Processes 1-2 and 3-4 are isen tropic (adiabatic), therefore T2  P 2    T1  P1 

( k 1) / k

( k 1) / k

Also, P2   P3 and P4  P 1 , therefore Equation (1) becomes  th  1 

where r p 

 P 2  P 

 

T3  P 3  , and    T4  P4   

T1 T2

T2 T1

1 



T 3 T4

T 4 T3

and

1 

T2 T3



T 1 T4  

1

  P 2      P 1 

( k 1) / k 

1 

1 r  p( k 1) / k 

is the pressure ratio of the compressor and the turbine

Jet Propulsion Cycle

T

4

P=constant qin 3

5 6

2 1

qout P=constant

1-2, inlet flow decelerates in the diffuser;  pressure and temperature increase •

5-6, outlet flow accelerates in the nozzle section, pressure and temperature decrease •

Propulsive Power  Jet Engine Mass flow out

Action force, FA

Mass flow in Inlet velocity, Vin

Exit velocity, Vexit

Reaction force, FR 

Due to the action force F , the momentum of the air flowing A

through the engine increases: F



A

( linear momentum change) = [

From Newton' s third law: F

A

F



R 

 (V m

exit





V  ) in

Propulsive Power 

 =FV W P

R

aircraft



 (V m

exit



V )V   in

aircraft  

d

( mV )] dt dt   F  Propulsive force  R



( mV )]

exit



[

d 

in



 mV

exit



   mV in

Gas Turbine Improvements Increase the gas combustion temperature (T 3) before it enters the turbine since th = 1 - (T4/T3)  Limited by metallurgical restriction: ceramic coating over the turbine blades  Improved intercooling technology: blow cool air over the surface of the blades (film cooling), steam cooling inside the  blades. •

Modifications to the basic thermodynamic cycle: intercooling, reheating, regeneration •

Improve design of turbomachinery components: multi-stage compressor and turbine configuration. Better aerodynamic design on blades (reduce stall). •

PW8000 Geared Turbofan Engine

Twin-spool configuration: H-P turbine drives H-P compressor  L-P turbine drives L-P compressor, on separated shafts Gearbox to further decrease the RPM of the fan More fuel efficiency Less noise Fewer engine parts From Machine Design Magazine •

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