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Journal Name International Journal of Civil AviationISSN 1943-3433

2009, Vol. 1, No. 1: E3

www.macrothink.org/ijca39

Compressor Effects on Specific Fuel Consumption of

Kerosene-fueled Civil Turbofans

Onder Turan (Corresponding author)

Aircraft Propulsion &Structure Maintenance Department, School of Civil Aviation,Anadolu University, PO Box 26470, Eskisehir, Turkey

Tel: +90-222-323-2722 E-mail: [email protected]

T. Hikmet Karakoc

Aircraft Propulsion &Structure Maintenance Department, School of Civil Aviation,Anadolu University

PO Box 26470, Eskisehir, Turkey

Tel: +90-222-323-2722 E-mail: [email protected]

Abstract

All gas turbine propulsion must have a compressor component that develops the pressure risespecified by the cycle. The main objective of the present study is to perform axial compressorpressure ratio effects on the specific fuel consumption of civil turbofans in both ideal and realcycles. At the beginning of this study, ideal and real cycle curves were drawn individually toexplain the compressor pressure ratio behavior on the specific fuel consumption in excel andvisual programming languages, respectively. At the second step, three dimensional responsesurfaces of the specific fuel consumption had been drawn according to the compressorpressure ratio. At the end of the study, real engines compressor data were marked on thesecurves and compared with results obtained in this paper.

Keywords: Turbofan, Compressor, Bypass ratio, Cycle analysis

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Compressors are, to a high degree of approximation, adiabatic. To overall efficiency used tomeasure a compressors performance is the isentropic efficiency c, defined by

ratiopressuregivenforncompressioof workactualratiopressuregivenforncompressioof workideal

=c (1)

The actual work per unit mass wc is h t3- h t2 [=C p(T t3-T t2)] and the ideal work per unit masswci=h t3i- h t2 [=C p(T t3i-T t2)]. Here, h t3i is the isentropic compressor leaving total enthalpy.Compressor isentropic efficiency can be written as follows:

23

23

t t

t it

c

cic hh

hh

w

w

== (2)

For a calorifically perfect gas, it can be written as Equation (3);

( )11

23

23

=

== cci

t t

t it p

c

cic

T T

T T C

w

w

(3)

In Equation (3) ci is the ideal compressor temperature ratio which is related to thecompressor pressure ratio by the isentropic relationship

( ) ( ) / c

/ cici

11 == (4)

Thus we have

( )

1

11

=

c

/ c

c

(5)

2. Compressor Pressure Ratio Effects on the Specific Fuel Consumption for Ideal andReal Cycles

The station numbering of a commercial turbofan can be shown engine in Figure 1. Stationnumbering is most important for thermodynamic study and energy analysis of air breathingengines. Ideal and real cycle equations were given in Appendix 1 and Appendix 2,respectively. Compressor pressure ratio effects on the specific fuel consumption ofcommercial turbofans for ideal and real cycles can be easily shown in Figure 2 and Figure 3.

Figure 1. Station numbering of commercial turbofan (Borguet, 2006)

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12

14

16

18

20

22

24

26

28

1 5 10 15 20 25 30

Compressor pressure ratio

S p e c

i f i c f u e l c o n s u m p t i o n

( g / k N

. s n ) =0,5

=1

=1,5

=2

=3

=4

=5

=8

=12

: bypass ratio

12

13

14

15

16

17

18

0 5 10 15 20 25 30 35


S p e c i f i c f u e l c o n s u m p t i o n [ g / ( k N

. s ) ]

x=0.5x=1

x=2x=5

x: bypass ratio

It can be observed in Figure 2 and Figure 3 that while the compressor pressure ratio increases,the specific fuel consumption decreases in ideal and real cycles. V2500, CFM56-7B andGE90-92B engines value are also shown in Figure 2 and Figure 3.

Figure 2. Specific fuel consumption variation with compressor pressure for ideal cycle

Figure 3. Specific fuel consumption variation with compressor pressure for real cycle

CFM56-7BV2500

GE90-92B

CFM56-7BV2500

GE90-92B

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3. Compressor Pressure Ratio Bypass Ratio Specific Fuel Consumption ResponseSurfaces

Compressor pressure ratio bypass ratio specific fuel consumption response surfaces weredeveloped by Turan (2008) in MATLAB programming environment. Parametric calculationcan be implemented for observing specific fuel consumption variation according to thecompressor pressure ratio and the bypass ratio as a three dimensional and color scaled plots.Specific fuel consumption variation with bypass ratio and compressor pressure ratio can beeasily shown in Figure 4 coupled with input parameters in Table 1.

Table 1. On-design parameters for compressor pressure ratio bypass ratio specific fuelconsumption plots

M 0 T 0 (K) h PR(kJ/kg) f

T 4(K) CpckJ/(kg.K)

CptkJ/(kg.K) c

t

0.8 220 43100 1.5 1500 1.00488 1.147 1.4 1.33

34 t t p / p 1319 t t p / p ec e f e t b m 9 p / 0 p 190 p / p

0.99 0.99 0.90 0.89 0.89 0.99 0.99 0.90 0.90

Figure 4. (a)

S p e c

i f i c f u e l c o n s u m p t

i o n

( g 7 k N

. s )


Bypass ratio

CFM56-7B

V2500

GE90-92B

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Borguet S., Kelner V., Leonard O. (2006), Cycle Optimization of a Turbine Engine: anApproach Based on Genetic Algorithms, [Online] Available http://www.ulg.ac.be/turbo/research/paper/ NCTAM2006.pdf (September 13, 2008)Mert M. (2008), Ideal cycle analysis of turbofan engines with excel program , Bachelor of

Science Thesis, Anadolu University, Eskisehir, Turkey.Turan O. (2000), Performance analysis and evaluation program of gas turbine engines ,Master of Science Thesis, Anadolu University, Eskisehir, Turkey.

Turan O. (2008), Elitism-based genetic algorithm of turbofan engines, PhD thesis, AnadoluUniversity , Eskisehir, Turkey.

Nomenclature

a Speed of sound, m/sCp Specific heat at constant pressure, kJ/(kg-K)Cv Specific heat at constant volume, kJ/(kg-K)

e Politropic efficiencyf Fuel air ratioF Thrust, kNFR Thrust ratio

F / 0m& Specific thrust, N.s/kg

gc Newtons constanthPR Fuel heating value, kJ/kgm& Mass flow rate, kg/s

M Mach numberP Pressure, PaR Universal gas constant, m 2 /(s 2-K)SFC Specific fuel consumption, g/(kN.s)T Temperature, KV Velocity, m/s Bypass ratiow specific work

Greek Letters

Efficiency Specific heat ratio Pressure ratio Temperature ratio Enthalpy ratio of combustion chamber

Subcripts and supercripts

b Burner

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c Compressord Diffusere Exitfn Fan nozzle

i IsentropicDB Duct bypassO OverallP Propulsivet TotalTH Thermal

Appendix

Appendix 1. Ideal cycle parametric equations for separate flow and no afterburning turbofan

Table E1. Input and output parameters for ideal parametric cycle

Input parameters

M 0 , T 0 , , c p , h PR , T t4 , c , f ,

Output parameters

0m / F & , SFC, TH , P, O,FR

Table E2. Ideal parametric cycle equations

Equation No Equation No

pC

R

1=

(e.1)

( )

+

+= 0

0

190

0

90

0 1 M

a

V M

V

V

ga

mF

c&

(e.9)

00 T Rga = (e.2) ( )

PR

cr p

h

T C f

= 0

(e.10)

201 M

r 2

1-+=

(e.3)( )( )01 m / F

f SFC &+

= (e.11)

0

4T C T C

p

t p =

(e.4)

cr TH

11 =

(e.12)

/ (cc

1)-=

(e.5) ( )( )2020219202029

001900902

M a / V M a / V

M a / V M a / V M P

+

+=

(e.13)

/ ( f f

1)-=

(e.6) PTH =0 (e.14)

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( )[ ]+=cr

f cr

aV

112

0

9

1-

(e.7)

0019

009

M a / V

M a / V FR

= (e.15)

{ }1

2

0

19 = f r

a

V

1-

(e.8)

Appendix 2. Real cycle parametric equations for separate flow and no afterburning turbofan

Table E3. Input and output parameters for real parametric cycle

Input parameters

M 0 , T 0 , c , C pc , t , c pt , h PR , dmax , b , fn

n , fn , e c , e f , e t , b , m , P 0 /P 9 , P 0 /P 19 , T t4 , c , f ,

Output parameters

0m / F & , SFC, TH , P, O

Table E4. Real parametric cycle equations

Equation No Equation No

pcc

cc C

R

1=

(e.16)

1-

1-1)/ -

c

(c

c

cc=

(e.25)

pt t

t t C

R

1=

(e.17) )e /(( f f

f cc 1)-

= (e.26)

00 T Rga ccc= (e.18)

1-

1-1)/ -

f

( f

f

cc

= (e.27)

000 M aV = (e.19)

pcbPR

cr

)T C /(h

f

-

-

0=

(e.28)

201 M

cr 2

1-+=

(e.20) ( )[ ]) f (

mt +

+=

1

11 f cr

1--

(e.29)

1)-cc /(r r =

(e.21) nt bcd r t ) p / p( p / p 9009 = (e.30)

r maxd d = (e.22)

= 1-1-

t

1)-

(t

t

t

) p

p(

M

0

99

2

(e.31)

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